using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Reflection;

using System.Reflection.Emit;

using System.Text;

using System.Collections.ObjectModel;

using System.Linq.Expressions;

using NPoco.Linq;



namespace NPoco.Expressions

{

    public class OrderByMember

    {

        public Type EntityType { get; set; }

        public PocoColumn PocoColumn { get; set; }

        public string AscDesc { get; set; }

    }



    public class SelectMember : IEquatable<SelectMember>

    {

        public Type EntityType { get; set; }

        public string SelectSql { get; set; }

        public PocoColumn PocoColumn { get; set; }



        public bool Equals(SelectMember other)

        {

            if (ReferenceEquals(null, other)) return false;

            if (ReferenceEquals(this, other)) return true;

            return Equals(EntityType, other.EntityType) && Equals(PocoColumn, other.PocoColumn);

        }



        public override bool Equals(object obj)

        {

            if (ReferenceEquals(null, obj)) return false;

            if (ReferenceEquals(this, obj)) return true;

            if (obj.GetType() != this.GetType()) return false;

            return Equals((SelectMember) obj);

        }



        public override int GetHashCode()

        {

            unchecked

            {

                return ((EntityType != null ? EntityType.GetHashCode() : 0)*397) ^ (PocoColumn != null ? PocoColumn.GetHashCode() : 0);

            }

        }

    }



    public class GeneralMember

    {

        public Type EntityType { get; set; }

        public PocoColumn PocoColumn { get; set; }

    }



    public interface ISqlExpression

    {

        List<OrderByMember> OrderByMembers { get; }

        int? Rows { get; }

        int? Skip { get; }

        string WhereSql { get; }

        object[] Params { get; }

        Type Type { get; }

        List<SelectMember> SelectMembers { get; }

        List<GeneralMember> GeneralMembers { get; }

        string ApplyPaging(string sql, IEnumerable<PocoColumn> columns);

    }



    public abstract class SqlExpression<T> : ISqlExpression

    {

        private Expression<Func<T, bool>> underlyingExpression;

        private List<string> orderByProperties = new List<string>();

        private List<OrderByMember> orderByMembers = new List<OrderByMember>();

        private List<SelectMember> selectMembers = new List<SelectMember>();

        private List<GeneralMember> generalMembers = new List<GeneralMember>();

        private string selectExpression = string.Empty;

        private string whereExpression;

        private string groupBy = string.Empty;

        private string havingExpression;

        private string orderBy = string.Empty;



        List<OrderByMember> ISqlExpression.OrderByMembers { get { return orderByMembers; } }

        List<SelectMember> ISqlExpression.SelectMembers { get { return selectMembers; } }

        List<GeneralMember> ISqlExpression.GeneralMembers { get { return generalMembers; } }

        string ISqlExpression.WhereSql { get { return whereExpression; } }

        int? ISqlExpression.Rows { get { return Rows; } }

        int? ISqlExpression.Skip { get { return Skip; } }

        Type ISqlExpression.Type { get { return _type; } }

        object[] ISqlExpression.Params { get { return Context.Params; } }



        string ISqlExpression.ApplyPaging(string sql, IEnumerable<PocoColumn> columns)

        {

            return ApplyPaging(sql, columns);

        }



        private string sep = string.Empty;

        private PocoData modelDef;

        private readonly IDatabase _database;

        private readonly DatabaseType _databaseType;

        private bool PrefixFieldWithTableName { get; set; }

        private bool WhereStatementWithoutWhereString { get; set; }

        private Type _type { get; set; }



        public SqlExpression(IDatabase database, bool prefixTableName)

        {

            _type = typeof(T);

            modelDef = database.PocoDataFactory.ForType(typeof(T));

            _database = database;

            _databaseType = database.DatabaseType;

            PrefixFieldWithTableName = prefixTableName;

            WhereStatementWithoutWhereString = false;

            paramPrefix = "@";

            Context = new SqlExpressionContext(this);

        }



        public class SqlExpressionContext

        {

            private readonly SqlExpression<T> _expression;



            public SqlExpressionContext(SqlExpression<T> expression)

            {

                _expression = expression;

                UpdateFields = new List<string>();

            }



            public List<string> UpdateFields { get; set; }

            public object[] Params { get { return _expression._params.ToArray(); } }



            public virtual string ToDeleteStatement()

            {

                return _expression.ToDeleteStatement();

            }



            public virtual string ToUpdateStatement(T item)

            {

                return _expression.ToUpdateStatement(item, false);

            }



            public virtual string ToUpdateStatement(T item, bool excludeDefaults)

            {

                return _expression.ToUpdateStatement(item, excludeDefaults);

            }



            public virtual string ToUpdateStatement(T item, bool excludeDefaults, bool allFields)

            {

                if (allFields)

                    _expression.generalMembers = _expression.GetAllMembers().Select(x => new GeneralMember { EntityType = typeof(T), PocoColumn = x }).ToList();



                return _expression.ToUpdateStatement(item, excludeDefaults);

            }



            public string ToWhereStatement()

            {

                return _expression.ToWhereStatement();

            }



            public virtual string ToSelectStatement()

            {

                return ToSelectStatement(true);

            }



            public virtual string ToSelectStatement(bool applyPaging)

            {

                return _expression.ToSelectStatement(applyPaging);

            }

        }



        /// <summary>

        /// Clear select expression. All properties will be selected.

        /// </summary>

        //public virtual SqlExpression<T> Select()

        //{

        //    return Select(string.Empty);

        //}



        /// <summary>

        /// set the specified selectExpression.

        /// </summary>

        /// <param name='selectExpression'>

        /// raw Select expression: "Select SomeField1, SomeField2 from SomeTable"

        /// </param>

        //public virtual SqlExpression<T> Select(string selectExpression)

        //{

        //    if (!string.IsNullOrEmpty(selectExpression))

        //    {

        //        this.selectExpression = selectExpression;

        //    }

        //    return this;

        //}



        /// <summary>

        /// Fields to be selected.

        /// </summary>

        /// <param name='fields'>

        /// x=> x.SomeProperty1 or x=> new{ x.SomeProperty1, x.SomeProperty2}

        /// </param>

        /// <typeparam name='TKey'>

        /// objectWithProperties

        /// </typeparam>

        public virtual SqlExpression<T> Select<TKey>(Expression<Func<T, TKey>> fields)

        {

            sep = string.Empty;

            selectMembers.Clear();

            Visit(fields);

            return this;

        } 

        

        public virtual List<SelectMember> SelectProjection<TKey>(Expression<Func<T, TKey>> fields)

        {

            sep = string.Empty;

            selectMembers.Clear();

            _projection = true;

            Visit(fields);

            _projection = false;

            var proj = new List<SelectMember>(selectMembers.Union(generalMembers.Select(x=>new SelectMember() { EntityType = x.EntityType, PocoColumn = x.PocoColumn, SelectSql = _databaseType.EscapeSqlIdentifier(x.PocoColumn.AutoAlias) })));

            selectMembers.Clear();

            return proj;

        }



        public virtual SqlExpression<T> SelectDistinct<TKey>(Expression<Func<T, TKey>> fields)

        {

            sep = string.Empty;

            selectMembers.Clear();

            var exp = PartialEvaluator.Eval(fields, CanBeEvaluatedLocally);

            Visit(exp);

            return this;

        }



        //public virtual SqlExpression<T> Where()

        //{

        //    if (underlyingExpression != null) underlyingExpression = null; //Where() clears the expression

        //    return Where(string.Empty);

        //}



        public virtual SqlExpression<T> Where(string sqlFilter, params object[] filterParams)

        {

            whereExpression = !string.IsNullOrEmpty(sqlFilter) ? sqlFilter : string.Empty;

            foreach (var filterParam in filterParams)

            {

                CreateParam(filterParam);

            }

            if (!string.IsNullOrEmpty(whereExpression)) whereExpression = (WhereStatementWithoutWhereString ? "" : "WHERE ") + whereExpression;

            return this;

        }



        public string On<T2>(Expression<Func<T, T2, bool>> predicate)

        {

            sep = " ";

            var onSql = Visit(predicate).ToString();

            return onSql;

        }



        public virtual SqlExpression<T> Where(Expression<Func<T, bool>> predicate)

        {

            if (predicate != null)

            {

                And(predicate);

            }

            else

            {

                underlyingExpression = null;

                whereExpression = string.Empty;

            }



            return this;

        }



        protected virtual SqlExpression<T> And(Expression<Func<T, bool>> predicate)

        {

            if (predicate != null)

            {

                if (underlyingExpression == null)

                    underlyingExpression = predicate;

                else

                    underlyingExpression = underlyingExpression.And(predicate);



                ProcessInternalExpression();

            }

            return this;

        }



        //public virtual SqlExpression<T> Or(Expression<Func<T, bool>> predicate)

        //{

        //    if (predicate != null)

        //    {

        //        if (underlyingExpression == null)

        //            underlyingExpression = predicate;

        //        else

        //            underlyingExpression = underlyingExpression.Or(predicate);



        //        ProcessInternalExpression();

        //    }

        //    return this;

        //}



        private void ProcessInternalExpression()

        {

            sep = " ";

            var exp = PartialEvaluator.Eval(underlyingExpression, CanBeEvaluatedLocally);

            whereExpression = Visit(exp).ToString();

            if (!string.IsNullOrEmpty(whereExpression)) whereExpression = (WhereStatementWithoutWhereString ? "" : "WHERE ") + whereExpression;

        }



        private bool CanBeEvaluatedLocally(Expression expression)

        {

            // any operation on a query can't be done locally

            ConstantExpression cex = expression as ConstantExpression;

            if (cex != null)

            {

                IQueryable query = cex.Value as IQueryable;

                if (query != null && query.Provider == this)

                    return false;

            }

            MethodCallExpression mc = expression as MethodCallExpression;

            if (mc != null &&

                (mc.Method.DeclaringType == typeof(Enumerable) ||

                 mc.Method.DeclaringType == typeof(Queryable)))

            {

                return false;

            }

            if (expression.NodeType == ExpressionType.Convert &&

                expression.Type == typeof(object))

                return true;

            return expression.NodeType != ExpressionType.Parameter &&

                   expression.NodeType != ExpressionType.Lambda;

        }



        //public virtual SqlExpression<T> GroupBy()

        //{

        //    return GroupBy(string.Empty);

        //}



        //public virtual SqlExpression<T> GroupBy(string groupBy)

        //{

        //    this.groupBy = groupBy;

        //    return this;

        //}



        public virtual SqlExpression<T> GroupBy<TKey>(Expression<Func<T, TKey>> keySelector)

        {

            sep = string.Empty;

            groupBy = Visit(keySelector).ToString();

            if (!string.IsNullOrEmpty(groupBy)) groupBy = string.Format("GROUP BY {0}", groupBy);

            return this;

        }



        //public virtual SqlExpression<T> Having()

        //{

        //    return Having(string.Empty);

        //}



        //public virtual SqlExpression<T> Having(string sqlFilter, params object[] filterParams)

        //{

        //    havingExpression = !string.IsNullOrEmpty(sqlFilter) ? sqlFilter : string.Empty;

        //    foreach (var filterParam in filterParams)

        //    {

        //        CreateParam(filterParam);

        //    }

        //    if (!string.IsNullOrEmpty(havingExpression)) havingExpression = "HAVING " + havingExpression;

        //    return this;

        //}



        //public virtual SqlExpression<T> Having(Expression<Func<T, bool>> predicate)

        //{



        //    if (predicate != null)

        //    {

        //        sep = " ";

        //        havingExpression = Visit(predicate).ToString();

        //        if (!string.IsNullOrEmpty(havingExpression)) havingExpression = "HAVING " + havingExpression;

        //    }

        //    else

        //        havingExpression = string.Empty;



        //    return this;

        //}







        //public virtual SqlExpression<T> OrderBy()

        //{

        //    return OrderBy(string.Empty);

        //}



        //public virtual SqlExpression<T> OrderBy(string orderBy)

        //{

        //    orderByProperties.Clear();

        //    this.orderBy = orderBy;

        //    return this;

        //}



        public virtual SqlExpression<T> OrderBy<TKey>(Expression<Func<T, TKey>> keySelector)

        {

            sep = string.Empty;

            orderByProperties.Clear();

            orderByMembers.Clear();

            generalMembers.Clear();

            var memberAccess = (MemberAccessString)Visit(keySelector);

            orderByProperties.Add(memberAccess + " ASC");

            orderByMembers.Add(new OrderByMember { AscDesc = "ASC", PocoColumn = memberAccess.PocoColumn, EntityType = memberAccess.Type});

            generalMembers.Clear();

            BuildOrderByClauseInternal();

            return this;

        }



        public virtual SqlExpression<T> ThenBy<TKey>(Expression<Func<T, TKey>> keySelector)

        {

            sep = string.Empty;

            generalMembers.Clear();

            var memberAccess = (MemberAccessString)Visit(keySelector);

            orderByProperties.Add(memberAccess + " ASC");

            orderByMembers.Add(new OrderByMember { AscDesc = "ASC", PocoColumn = memberAccess.PocoColumn, EntityType = memberAccess.Type });

            generalMembers.Clear();

            BuildOrderByClauseInternal();

            return this;

        }



        public virtual SqlExpression<T> OrderByDescending<TKey>(Expression<Func<T, TKey>> keySelector)

        {

            sep = string.Empty;

            orderByProperties.Clear();

            orderByMembers.Clear();

            generalMembers.Clear();

            var memberAccess = (MemberAccessString)Visit(keySelector);

            orderByProperties.Add(memberAccess + " DESC");

            orderByMembers.Add(new OrderByMember { AscDesc = "DESC", PocoColumn = memberAccess.PocoColumn, EntityType = memberAccess.Type });

            generalMembers.Clear();

            BuildOrderByClauseInternal();

            return this;

        }



        public virtual SqlExpression<T> ThenByDescending<TKey>(Expression<Func<T, TKey>> keySelector)

        {

            sep = string.Empty;

            generalMembers.Clear();

            var memberAccess = (MemberAccessString)Visit(keySelector);

            orderByProperties.Add(memberAccess + " DESC");

            orderByMembers.Add(new OrderByMember { AscDesc = "DESC", PocoColumn = memberAccess.PocoColumn, EntityType = memberAccess.Type });

            generalMembers.Clear();

            BuildOrderByClauseInternal();

            return this;

        }



        private void BuildOrderByClauseInternal()

        {

            if (orderByMembers.Count > 0)

            {

                orderBy = "ORDER BY " + string.Join(", ", orderByMembers.Select(x => (PrefixFieldWithTableName ? _databaseType.EscapeSqlIdentifier(x.PocoColumn.AutoAlias) : _databaseType.EscapeSqlIdentifier(x.PocoColumn.ColumnName)) + " " + x.AscDesc).ToArray());

            }

            else

            {

                orderBy = null;

            }

        }





        /// <summary>

        /// Set the specified offset and rows for SQL Limit clause.

        /// </summary>

        /// <param name='skip'>

        /// Offset of the first row to return. The offset of the initial row is 0

        /// </param>

        /// <param name='rows'>

        /// Number of rows returned by a SELECT statement

        /// </param>	

        public virtual SqlExpression<T> Limit(int skip, int rows)

        {

            Rows = rows;

            Skip = skip;

            return this;

        }



        /// <summary>

        /// Set the specified rows for Sql Limit clause.

        /// </summary>

        /// <param name='rows'>

        /// Number of rows returned by a SELECT statement

        /// </param>

        public virtual SqlExpression<T> Limit(int rows)

        {

            Rows = rows;

            Skip = 0;

            return this;

        }



        /// <summary>

        /// Clear Sql Limit clause

        /// </summary>

        //public virtual SqlExpression<T> Limit()

        //{

        //    Skip = null;

        //    Rows = null;

        //    return this;

        //}





        /// <summary>

        /// Fields to be updated.

        /// </summary>

        /// <param name='updatefields'>

        /// IList<string> containing Names of properties to be updated

        /// </param>

        //public virtual SqlExpression<T> Update(IList<string> updateFields)

        //{

        //    this.updateFields = updateFields;

        //    return this;

        //}



        /// <summary>

        /// Fields to be updated.

        /// </summary>

        /// <param name='fields'>

        /// x=> x.SomeProperty1 or x=> new{ x.SomeProperty1, x.SomeProperty2}

        /// </param>

        /// <typeparam name='TKey'>

        /// objectWithProperties

        /// </typeparam>

        public virtual SqlExpression<T> Update<TKey>(Expression<Func<T, TKey>> fields)

        {

            sep = string.Empty;

            generalMembers.Clear();

            Visit(fields);

            Context.UpdateFields = new List<string>(generalMembers.Select(x => x.PocoColumn.ColumnName));

            generalMembers.Clear();

            return this;

        }



        /// <summary>

        /// Clear UpdateFields list ( all fields will be updated)

        /// </summary>

        //public virtual SqlExpression<T> Update()

        //{

        //    this.updateFields = new List<string>();

        //    return this;

        //}



        /// <summary>

        /// Fields to be inserted.

        /// </summary>

        /// <param name='fields'>

        /// x=> x.SomeProperty1 or x=> new{ x.SomeProperty1, x.SomeProperty2}

        /// </param>

        /// <typeparam name='TKey'>

        /// objectWithProperties

        /// </typeparam>

        //public virtual SqlExpression<T> Insert<TKey>(Expression<Func<T, TKey>> fields)

        //{

        //    sep = string.Empty;

        //    Context.InsertFields = Visit(fields).ToString().Split(',').ToList();

        //    return this;

        //}



        /// <summary>

        /// fields to be inserted.

        /// </summary>

        /// <param name='insertFields'>

        /// IList&lt;string&gt; containing Names of properties to be inserted

        /// </param>

        //public virtual SqlExpression<T> Insert(IList<string> insertFields)

        //{

        //    this.insertFields = insertFields;

        //    return this;

        //}



        /// <summary>

        /// Clear InsertFields list ( all fields will be inserted)

        /// </summary>

        //public virtual SqlExpression<T> Insert()

        //{

        //    this.insertFields = new List<string>();

        //    return this;

        //}



        protected virtual string ToDeleteStatement()

        {

            return string.Format("DELETE {0} FROM {1} {2}",

                (PrefixFieldWithTableName ? _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias) : string.Empty),

                _databaseType.EscapeTableName(modelDef.TableInfo.TableName) + (PrefixFieldWithTableName ? " " + _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias) : string.Empty),

                WhereExpression);

        }



        protected virtual string ToUpdateStatement(T item)

        {

            return ToUpdateStatement(item, false);

        }



        protected virtual string ToUpdateStatement(T item, bool excludeDefaults)

        {

            var setFields = new StringBuilder();



            foreach (var fieldDef in modelDef.Columns)

            {

                if (Context.UpdateFields.Count > 0 && !Context.UpdateFields.Contains(fieldDef.Value.MemberInfo.Name)) continue; // added

                object value = fieldDef.Value.GetValue(item);

                if (_database.Mapper != null)

                {

                    var converter = _database.Mapper.GetToDbConverter(fieldDef.Value.ColumnType, fieldDef.Value.MemberInfo.GetMemberInfoType());

                    if (converter != null)

                        value = converter(value);

                }



                if (excludeDefaults && (value == null || value.Equals(MappingFactory.GetDefault(value.GetType())))) continue; //GetDefaultValue?



                if (setFields.Length > 0)

                    setFields.Append(", ");



                setFields.AppendFormat("{0} = {1}", (PrefixFieldWithTableName ? _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias) + "." : string.Empty) + _databaseType.EscapeSqlIdentifier(fieldDef.Value.ColumnName), CreateParam(value));

            }



            if (PrefixFieldWithTableName)

                return string.Format("UPDATE {0} SET {2} FROM {1} {3}", _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias), _databaseType.EscapeTableName(modelDef.TableInfo.TableName) + " " + _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias), setFields, WhereExpression);

            else

                return string.Format("UPDATE {0} SET {1} {2}", _databaseType.EscapeTableName(modelDef.TableInfo.TableName), setFields, WhereExpression);

        }



        protected string ToWhereStatement()

        {

            return WhereExpression;

        }



        protected virtual string ToSelectStatement(bool applyPaging)

        {

            var sql = new StringBuilder();



            sql.Append(SelectExpression);

            sql.Append(string.IsNullOrEmpty(WhereExpression) ?

                       "" :

                       " \n" + WhereExpression);

            sql.Append(string.IsNullOrEmpty(GroupByExpression) ?

                       "" :

                       " \n" + GroupByExpression);

            sql.Append(string.IsNullOrEmpty(HavingExpression) ?

                       "" :

                       " \n" + HavingExpression);

            sql.Append(string.IsNullOrEmpty(OrderByExpression) ?

                       "" :

                       " \n" + OrderByExpression);



            return applyPaging ? ApplyPaging(sql.ToString(), ModelDef.QueryColumns.Select(x=>x.Value)) : sql.ToString();

        }



        //public virtual string ToCountStatement()

        //{

        //    return OrmLiteConfig.DialectProvider.ToCountStatement(modelDef.ModelType, WhereExpression, null);

        //}



        private string SelectExpression

        {

            get

            {

                var selectMembersFromOrderBys = orderByMembers

                    .Select(x => new SelectMember() { PocoColumn = x.PocoColumn, EntityType = x.EntityType})

                    .Where(x => !selectMembers.Any(y => y.EntityType == x.EntityType && y.PocoColumn.MemberInfo.Name == x.PocoColumn.MemberInfo.Name));



                var morecols = selectMembers.Concat(selectMembersFromOrderBys);

                var cols = selectMembers.Count == 0 ? null : morecols.ToList();

                BuildSelectExpression(cols, false);

                return selectExpression;

            }

            set

            {

                selectExpression = value;

            }

        }



        private string WhereExpression

        {

            get

            {

                return whereExpression;

            }

            set

            {

                whereExpression = value;

            }

        }



        private string GroupByExpression

        {

            get

            {

                return groupBy;

            }

            set

            {

                groupBy = value;

            }

        }



        private string HavingExpression

        {

            get

            {

                return havingExpression;

            }

            set

            {

                havingExpression = value;

            }

        }





        private string OrderByExpression

        {

            get

            {

                return orderBy;

            }

            set

            {

                orderBy = value;

            }

        }



        protected virtual string LimitExpression

        {

            get

            {

                if (!Skip.HasValue) return "";

                string rows;

                if (Rows.HasValue)

                {

                    rows = string.Format(",{0}", Rows.Value);

                }

                else

                {

                    rows = string.Empty;

                }

                return string.Format("LIMIT {0}{1}", Skip.Value, rows);

            }

        }



        private int? Rows { get; set; }

        private int? Skip { get; set; }



        protected internal PocoData ModelDef

        {

            get

            {

                return modelDef;

            }

            set

            {

                modelDef = value;

            }

        }



        protected internal virtual object Visit(Expression exp)

        {



            if (exp == null) return string.Empty;

            switch (exp.NodeType)

            {

                case ExpressionType.Lambda:

                    return VisitLambda(exp as LambdaExpression);

                case ExpressionType.MemberAccess:

                    return VisitMemberAccess(exp as MemberExpression);

                case ExpressionType.Constant:

                    return VisitConstant(exp as ConstantExpression);

                case ExpressionType.Add:

                case ExpressionType.AddChecked:

                case ExpressionType.Subtract:

                case ExpressionType.SubtractChecked:

                case ExpressionType.Multiply:

                case ExpressionType.MultiplyChecked:

                case ExpressionType.Divide:

                case ExpressionType.Modulo:

                case ExpressionType.And:

                case ExpressionType.AndAlso:

                case ExpressionType.Or:

                case ExpressionType.OrElse:

                case ExpressionType.LessThan:

                case ExpressionType.LessThanOrEqual:

                case ExpressionType.GreaterThan:

                case ExpressionType.GreaterThanOrEqual:

                case ExpressionType.Equal:

                case ExpressionType.NotEqual:

                case ExpressionType.Coalesce:

                case ExpressionType.ArrayIndex:

                case ExpressionType.RightShift:

                case ExpressionType.LeftShift:

                case ExpressionType.ExclusiveOr:

                    //return "(" + VisitBinary(exp as BinaryExpression) + ")";

                    return VisitBinary(exp as BinaryExpression);

                case ExpressionType.Conditional:

                    return VisitConditional(exp as ConditionalExpression);

                case ExpressionType.Negate:

                case ExpressionType.NegateChecked:

                case ExpressionType.Not:

                case ExpressionType.Convert:

                case ExpressionType.ConvertChecked:

                case ExpressionType.ArrayLength:

                case ExpressionType.Quote:

                case ExpressionType.TypeAs:

                    return VisitUnary(exp as UnaryExpression);

                case ExpressionType.Parameter:

                    return VisitParameter(exp as ParameterExpression);

                case ExpressionType.Call:

                    return VisitMethodCall(exp as MethodCallExpression);

                case ExpressionType.New:

                    return VisitNew(exp as NewExpression);

                case ExpressionType.NewArrayInit:

                case ExpressionType.NewArrayBounds:

                    return VisitNewArray(exp as NewArrayExpression);

                case ExpressionType.MemberInit:

                    return this.VisitMemberInit((MemberInitExpression)exp);

                default:

                    return exp.ToString();

            }

        }

        protected virtual Expression VisitMemberInit(MemberInitExpression init)

        {

            NewExpression n = init.NewExpression;

            IEnumerable<MemberBinding> bindings = this.VisitBindingList(init.Bindings);

            if (n != init.NewExpression || bindings != init.Bindings)

            {

                return Expression.MemberInit(n, bindings);

            }

            return init;

        }



        protected virtual IEnumerable<MemberBinding> VisitBindingList(ReadOnlyCollection<MemberBinding> original)

        {

            for (int i = 0, n = original.Count; i < n; i++)

            {

                this.VisitBinding(original[i]);

            }

            return original;

        }



        protected virtual object VisitBinding(MemberBinding binding)

        {

            switch (binding.BindingType)

            {

                case MemberBindingType.Assignment:

                    return this.VisitMemberAssignment((MemberAssignment)binding);

                case MemberBindingType.MemberBinding:

                    return this.VisitMemberMemberBinding((MemberMemberBinding)binding);

                //case MemberBindingType.ListBinding:

                //    return this.VisitMemberListBinding((MemberListBinding)binding);

                default:

                    throw new Exception(string.Format("Unhandled binding type '{0}'", binding.BindingType));

            }

        }



        protected virtual object VisitMemberMemberBinding(MemberMemberBinding binding)

        {

            return VisitBindingList(binding.Bindings);

        }



        protected virtual object VisitMemberAssignment(MemberAssignment assignment)

        {

            return this.Visit(assignment.Expression);

        }

        

        protected virtual object VisitLambda(LambdaExpression lambda)

        {

            if (lambda.Body.NodeType == ExpressionType.MemberAccess && sep == " ")

            {

                MemberExpression m = lambda.Body as MemberExpression;



                if (m.Expression != null)

                {

                    if (IsNullableMember(m))

                    {

                        string r = VisitMemberAccess(m.Expression as MemberExpression).ToString();

                        return string.Format("{0} is not null", r);

                    }

                    else

                    {

                        string r = VisitMemberAccess(m).ToString();

                        return string.Format("{0}={1}", r, GetQuotedTrueValue());

                    }

                }



            }

            return Visit(lambda.Body);

        }



        private static bool IsNullableMember(MemberExpression m)

        {

            var member = m.Expression as MemberExpression;

            return member != null

                && (m.Member.Name == "HasValue")

                && member.Type.IsGenericType && member.Type.GetGenericTypeDefinition() == typeof(Nullable<>);

        }



        protected virtual object VisitBinary(BinaryExpression b)

        {

            object left, right;

            var operand = BindOperant(b.NodeType);   //sep= " " ??

            if (operand == "AND" || operand == "OR")

            {

                var m = b.Left as MemberExpression;

                if (m != null && m.Expression != null

                    && m.Expression.NodeType == ExpressionType.Parameter)

                    left = new PartialSqlString(string.Format("{0} = {1}", VisitMemberAccess(m), GetQuotedTrueValue()));

                else

                    left = Visit(b.Left);



                m = b.Right as MemberExpression;

                if (m != null && m.Expression != null

                    && m.Expression.NodeType == ExpressionType.Parameter)

                    right = new PartialSqlString(string.Format("{0} = {1}", VisitMemberAccess(m), GetQuotedTrueValue()));

                else

                    right = Visit(b.Right);



                if (left as PartialSqlString == null && right as PartialSqlString == null)

                {

                    var result = Expression.Lambda(b).Compile().DynamicInvoke();

                    return new PartialSqlString(CreateParam(result));

                }



                if (left as PartialSqlString == null)

                    left = ((bool)left) ? GetTrueExpression() : GetFalseExpression();

                if (right as PartialSqlString == null)

                    right = ((bool)right) ? GetTrueExpression() : GetFalseExpression();

            }

            else

            {

                left = Visit(b.Left);

                right = Visit(b.Right);



                if (left as EnumMemberAccess != null && right as PartialSqlString == null)

                {

                    var pc = ((EnumMemberAccess)left).PocoColumn;



                    long numvericVal;

                    if (pc.ColumnType == typeof(string))

                        right = CreateParam(Enum.Parse(pc.MemberInfo.GetMemberInfoType(), right.ToString()).ToString());

                    else if (Int64.TryParse(right.ToString(), out numvericVal))

                        right = CreateParam(Enum.ToObject(pc.MemberInfo.GetMemberInfoType(), numvericVal));

                    else

                        right = CreateParam(right);

                }

                else if (left as NullableMemberAccess != null && right as PartialSqlString == null)

                {

                    operand = ((bool)right) ? "is not" : "is";

                    right = new PartialSqlString("null");

                }

                else if (right as EnumMemberAccess != null && left as PartialSqlString == null)

                {

                    var pc = ((EnumMemberAccess)right).PocoColumn;



                    //enum value was returned by Visit(b.Left)

                    long numvericVal;

                    if (pc.ColumnType == typeof(string))

                        left = CreateParam(Enum.Parse(pc.MemberInfo.GetMemberInfoType(), left.ToString()).ToString());

                    else if (Int64.TryParse(left.ToString(), out numvericVal))

                        left = CreateParam(Enum.ToObject(pc.MemberInfo.GetMemberInfoType(), numvericVal));

                    else

                        left = CreateParam(left);

                }

                else if (left as PartialSqlString == null && right as PartialSqlString == null)

                {

                    var result = Expression.Lambda(b).Compile().DynamicInvoke();

                    return result;

                }

                else if (left as PartialSqlString == null)

                    left = CreateParam(left);

                else if (right as PartialSqlString == null)

                    right = CreateParam(right);



            }



            if (operand == "=" && right.ToString().Equals("null", StringComparison.InvariantCultureIgnoreCase)) operand = "is";

            else if (operand == "<>" && right.ToString().Equals("null", StringComparison.InvariantCultureIgnoreCase)) operand = "is not";



            switch (operand)

            {

                case "MOD":

                case "COALESCE":

                    return new PartialSqlString(string.Format("{0}({1},{2})", operand, left, right));

                default:

                    return new PartialSqlString("(" + left + sep + operand + sep + right + ")");

            }

        }



        protected virtual object VisitMemberAccess(MemberExpression m)

        {

            bool isNull = false;



            if (IsNullableMember(m))

            {

                m = m.Expression as MemberExpression;

                isNull = true;

            }



            if (m.Expression != null

                && (m.Expression.NodeType == ExpressionType.Parameter

                    || m.Expression.NodeType == ExpressionType.Convert

                    || m.Expression.NodeType == ExpressionType.MemberAccess))

            {

                var propertyInfo = (PropertyInfo)m.Member;



                var type = GetCorrectType(m);

                var localModelDef = _database.PocoDataFactory.ForType(type);

                var pocoColumn = localModelDef.Columns.Values.Single(x => x.MemberInfo.Name == m.Member.Name);



                var columnName = (PrefixFieldWithTableName ? _databaseType.EscapeTableName(localModelDef.TableInfo.AutoAlias) + "." : "")

                                    + _databaseType.EscapeSqlIdentifier(pocoColumn.ColumnName);



                generalMembers.Add(new GeneralMember() { EntityType = type, PocoColumn = pocoColumn });



                if (isNull)

                    return new NullableMemberAccess(pocoColumn, columnName, type);



                if (propertyInfo.PropertyType.IsEnum)

                    return new EnumMemberAccess(pocoColumn, columnName, type);



                return new MemberAccessString(pocoColumn, columnName, type);

            }



            var memberExp = Expression.Convert(m, typeof(object));

            var lambda = Expression.Lambda<Func<object>>(memberExp);

            var getter = lambda.Compile();

            return getter();

        }



        private Type GetCorrectType(MemberExpression m)

        {

            var type = m.Member.DeclaringType;

            if (m.Expression.NodeType == ExpressionType.MemberAccess)

            {

                type = ((PropertyInfo)((MemberExpression)m.Expression).Member).PropertyType;

            }

            else if (m.Expression.NodeType == ExpressionType.Parameter)

            {

                type = m.Expression.Type;

            }

            return type;

        }

        

        protected virtual object VisitNew(NewExpression nex)

        {

            var member = Expression.Convert(nex, typeof(object));

            var lambda = Expression.Lambda<Func<object>>(member);

            try

            {

                var getter = lambda.Compile();

                return getter();

            }

            catch (System.InvalidOperationException)

            {

                List<MemberAccessString> exprs = VisitExpressionList(nex.Arguments).OfType<MemberAccessString>().ToList();

                StringBuilder r = new StringBuilder();

                for (int i = 0; i < exprs.Count; i++)

                {

                    if (_projection)

                    {

                        selectMembers.Add(new SelectMember()

                        {

                            EntityType = exprs[i].Type,

                            PocoColumn = exprs[i].PocoColumn,

                            SelectSql = exprs[i].Text

                        });

                        continue;

                    }



                    r.AppendFormat("{0}{1}", r.Length > 0 ? "," : "", exprs[i]);

                    if (nex.Members[i] != null)

                    {

                        var col = modelDef.Columns.SingleOrDefault(x => x.Value.MemberInfo.Name == nex.Members[i].Name);

                        if (col.Value != null)

                        {

                            var sel = new SelectMember()

                            {

                                EntityType = modelDef.type,

                                SelectSql = exprs[i].ToString(),

                                PocoColumn = col.Value

                            };

                            var memberName = _databaseType.EscapeSqlIdentifier(col.Value.ColumnName);

                            if (memberName != exprs[i].ToString())

                            {

                                var al = string.Format(" AS {0}", _databaseType.EscapeSqlIdentifier(col.Value.AutoAlias));

                                r.AppendFormat(al);

                                sel.SelectSql += al;

                            }

                            selectMembers.Add(sel);

                        }

                    }

                }

                return r.ToString();

            }



        }



        protected virtual object VisitParameter(ParameterExpression p)

        {

            return p.Name;

        }



        List<object> _params = new List<object>();

        int _paramCounter = 0;

        string paramPrefix;

        private bool _projection;

        public SqlExpressionContext Context { get; private set; }



        protected virtual object VisitConstant(ConstantExpression c)

        {

            if (c.Value == null)

                return new PartialSqlString("null");



            return c.Value;

        }



        protected virtual object VisitConditional(ConditionalExpression conditional)

        {

            sep = " ";

            var test = Visit(conditional.Test);

            var trueSql = Visit(conditional.IfTrue);

            var falseSql = Visit(conditional.IfFalse);



            return new PartialSqlString(string.Format("(case when {0} then {1} else {2} end)", test, trueSql, falseSql));

        }



        private string CreateParam(object value)

        {

            string paramPlaceholder = paramPrefix + _paramCounter++;

            _params.Add(value);

            return paramPlaceholder;

        }



        protected virtual object VisitUnary(UnaryExpression u)

        {

            switch (u.NodeType)

            {

                case ExpressionType.Not:

                    var o = Visit(u.Operand);



                    if (o as PartialSqlString == null)

                        return !((bool)o);



                    if (o as MemberAccessString != null)

                    {

                        if (o as NullableMemberAccess != null)

                            o = o + " is not null";

                        else

                            o = o + " = " + GetQuotedTrueValue();

                    }



                    return new PartialSqlString("NOT (" + o + ")");

                case ExpressionType.Convert:

                    if (u.Method != null)

                        return Expression.Lambda(u).Compile().DynamicInvoke();

                    break;

            }



            return Visit(u.Operand);



        }



        private bool IsColumnAccess(MethodCallExpression m)

        {

            if (m.Object != null && m.Object as MethodCallExpression != null)

                return IsColumnAccess(m.Object as MethodCallExpression);



            var exp = m.Object as MemberExpression;

            return exp != null

                && exp.Expression != null

                && ((exp.Expression.Type == typeof(T) && exp.Expression.NodeType == ExpressionType.Parameter

                    || exp.Expression.NodeType == ExpressionType.MemberAccess));

        }



        protected virtual object VisitMethodCall(MethodCallExpression m)

        {

            if (m.Method.DeclaringType == typeof(S))

                return VisitSqlMethodCall(m);



            if (IsStaticArrayMethod(m))

                return VisitStaticArrayMethodCall(m);



            if (IsEnumerableMethod(m))

                return VisitEnumerableMethodCall(m);



            if (IsColumnAccess(m))

                return VisitColumnAccessMethod(m);



            return Expression.Lambda(m).Compile().DynamicInvoke();

        }



        private bool IsStaticArrayMethod(MethodCallExpression m)

        {

            if (m.Object == null && m.Method.Name == "Contains")

            {

                return m.Arguments.Count == 2;

            }



            return false;

        }



        private bool IsEnumerableMethod(MethodCallExpression m)

        {

            if (m.Object != null

                && m.Object.Type.IsOrHasGenericInterfaceTypeOf(typeof(IEnumerable<>))

                && m.Object.Type != typeof(string)

                && m.Method.Name == "Contains")

            {

                return m.Arguments.Count == 1;

            }



            return false;

        }



        protected virtual object VisitEnumerableMethodCall(MethodCallExpression m)

        {

            switch (m.Method.Name)

            {

                case "Contains":

                    List<Object> args = this.VisitExpressionList(m.Arguments);

                    object quotedColName = args[0];

                    return BuildInStatement(m.Object, quotedColName);



                default:

                    throw new NotSupportedException();

            }

        }



        protected virtual object VisitStaticArrayMethodCall(MethodCallExpression m)

        {

            switch (m.Method.Name)

            {

                case "Contains":

                    List<Object> args = this.VisitExpressionList(m.Arguments);

                    object quotedColName = args[1];



                    Expression memberExpr = m.Arguments[0];

                    if (memberExpr.NodeType == ExpressionType.MemberAccess)

                        memberExpr = (m.Arguments[0] as MemberExpression);



                    return BuildInStatement(memberExpr, quotedColName);



                default:

                    throw new NotSupportedException();

            }

        }



        private StringBuilder FlattenList(IEnumerable inArgs)

        {

            StringBuilder sIn = new StringBuilder();

            foreach (Object e in inArgs)

            {

                if (!typeof(ICollection).IsAssignableFrom(e.GetType()))

                {

                    sIn.AppendFormat("{0}{1}", sIn.Length > 0 ? "," : "", CreateParam(e));

                }

                else

                {

                    var listArgs = e as ICollection;

                    foreach (Object el in listArgs)

                    {

                        sIn.AppendFormat("{0}{1}", sIn.Length > 0 ? "," : "", CreateParam(el));

                    }

                }

            }



            if (sIn.Length == 0)

            {

                sIn.AppendFormat("select 1 /*poco_dual*/ where 1 = 0");

            }

            return sIn;

        }



        protected virtual List<Object> VisitExpressionList(ReadOnlyCollection<Expression> original)

        {

            List<Object> list = new List<Object>();

            for (int i = 0, n = original.Count; i < n; i++)

            {

                if (original[i].NodeType == ExpressionType.NewArrayInit ||

                 original[i].NodeType == ExpressionType.NewArrayBounds)

                {



                    list.AddRange(VisitNewArrayFromExpressionList(original[i] as NewArrayExpression));

                }

                else

                    list.Add(Visit(original[i]));



            }

            return list;

        }



        protected virtual List<Object> VisitConstantList(ReadOnlyCollection<Expression> original)

        {

            List<Object> list = new List<Object>();

            for (int i = 0, n = original.Count; i < n; i++)

            {

                list.Add(original[i].GetConstantValue<object>());

            }

            return list;

        }



        protected virtual object VisitNewArray(NewArrayExpression na)

        {



            List<Object> exprs = VisitExpressionList(na.Expressions);

            StringBuilder r = new StringBuilder();

            foreach (Object e in exprs)

            {

                r.Append(r.Length > 0 ? "," + e : e);

            }



            return r.ToString();

        }



        protected virtual List<Object> VisitNewArrayFromExpressionList(NewArrayExpression na)

        {



            List<Object> exprs = VisitExpressionList(na.Expressions);

            return exprs;

        }





        protected virtual string BindOperant(ExpressionType e)

        {



            switch (e)

            {

                case ExpressionType.Equal:

                    return "=";

                case ExpressionType.NotEqual:

                    return "<>";

                case ExpressionType.GreaterThan:

                    return ">";

                case ExpressionType.GreaterThanOrEqual:

                    return ">=";

                case ExpressionType.LessThan:

                    return "<";

                case ExpressionType.LessThanOrEqual:

                    return "<=";

                case ExpressionType.AndAlso:

                    return "AND";

                case ExpressionType.OrElse:

                    return "OR";

                case ExpressionType.Add:

                    return "+";

                case ExpressionType.Subtract:

                    return "-";

                case ExpressionType.Multiply:

                    return "*";

                case ExpressionType.Divide:

                    return "/";

                case ExpressionType.Modulo:

                    return "MOD";

                case ExpressionType.Coalesce:

                    return "COALESCE";

                default:

                    return e.ToString();

            }

        }



        protected virtual string GetQuotedColumnName(string memberName)

        {

            var fd = modelDef.Columns.Values.FirstOrDefault(x => x.MemberInfo.Name == memberName);

            string fn = fd != null ? fd.ColumnName : memberName;

            return _databaseType.EscapeSqlIdentifier(fn);

        }



        protected string RemoveQuoteFromAlias(string exp)

        {



            if ((exp.StartsWith("\"") || exp.StartsWith("`") || exp.StartsWith("'"))

                && (exp.EndsWith("\"") || exp.EndsWith("`") || exp.EndsWith("'")))

            {

                exp = exp.Remove(0, 1);

                exp = exp.Remove(exp.Length - 1, 1);

            }

            return exp;

        }



        protected object GetTrueExpression()

        {

            return new PartialSqlString(string.Format("({0}={1})", GetQuotedTrueValue(), GetQuotedTrueValue()));

        }



        protected object GetFalseExpression()

        {

            return new PartialSqlString(string.Format("({0}={1})", GetQuotedTrueValue(), GetQuotedFalseValue()));

        }



        protected object GetQuotedTrueValue()

        {

            return CreateParam(true);

        }



        protected object GetQuotedFalseValue()

        {

            return CreateParam(false);

        }



        private void BuildSelectExpression(List<SelectMember> fields, bool distinct)

        {

            var cols = fields ?? modelDef.QueryColumns.Select(x => new SelectMember{ PocoColumn = x.Value, EntityType = modelDef.type });

            selectExpression = string.Format("SELECT {0}{1} \nFROM {2}",

                (distinct ? "DISTINCT " : ""),

                    string.Join(", ", cols.Select(x =>

                    {

                        if (x.SelectSql == null)

                            return (PrefixFieldWithTableName

                                ? _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias) + "." + _databaseType.EscapeSqlIdentifier(x.PocoColumn.ColumnName) + " as " + _databaseType.EscapeSqlIdentifier(x.PocoColumn.AutoAlias)

                                : _databaseType.EscapeSqlIdentifier(x.PocoColumn.ColumnName));

                        return x.SelectSql;

                    }).ToArray()),

                    _databaseType.EscapeTableName(modelDef.TableInfo.TableName) + (PrefixFieldWithTableName ? " " + _databaseType.EscapeTableName(modelDef.TableInfo.AutoAlias) : string.Empty));

        }



        internal List<PocoColumn> GetAllMembers()

        {

            return modelDef.Columns.Values.ToList();

        }



        protected virtual string ApplyPaging(string sql, IEnumerable<PocoColumn> columns)

        {

            if (!Rows.HasValue || Rows == 0)

                return sql;



            string sqlPage;

            var parms = _params.Select(x => x).ToArray();



            // Split the SQL

            PagingHelper.SQLParts parts;

            if (!PagingHelper.SplitSQL(sql, out parts)) throw new Exception("Unable to parse SQL statement for paged query");



            if (columns != null && columns.Any() && _databaseType.UseColumnAliases()) 

                parts.sqlColumns = string.Join(", ", columns.Select(x => _databaseType.EscapeSqlIdentifier(x.AutoAlias)).ToArray());



            sqlPage = _databaseType.BuildPageQuery(Skip ?? 0, Rows ?? 0, parts, ref parms);



            _params.Clear();

            _params.AddRange(parms);



            return sqlPage;

        }



        private string BuildInStatement(Expression m, object quotedColName)

        {

            string statement;

            var member = Expression.Convert(m, typeof(object));

            var lambda = Expression.Lambda<Func<object>>(member);

            var getter = lambda.Compile();



            if (quotedColName == null)

                quotedColName = Visit(m);



            var inArgs = getter() as IEnumerable;



            var sIn = FlattenList(inArgs);



            statement = string.Format("{0} {1} ({2})", quotedColName, "IN", sIn);

            return statement;

        }



        protected virtual object VisitSqlMethodCall(MethodCallExpression m)

        {

            List<Object> args = this.VisitExpressionList(m.Arguments);

            object quotedColName = args[0];

            args.RemoveAt(0);



            string statement;



            switch (m.Method.Name)

            {

                case "In":

                    statement = BuildInStatement(m.Arguments[1], quotedColName);

                    break;

                case "Desc":

                    statement = string.Format("{0} DESC", quotedColName);

                    break;

                case "As":

                    statement = string.Format("{0} As {1}", quotedColName,

                        _databaseType.EscapeSqlIdentifier(RemoveQuoteFromAlias(args[0].ToString())));

                    break;

                case "Sum":

                case "Count":

                case "Min":

                case "Max":

                case "Avg":

                    statement = string.Format("{0}({1}{2})",

                                         m.Method.Name.ToUpper(),

                                         quotedColName,

                                         args.Count == 1 ? string.Format(",{0}", args[0]) : "");

                    break;

                default:

                    throw new NotSupportedException();

            }



            return new PartialSqlString(statement);

        }



        protected virtual object VisitColumnAccessMethod(MethodCallExpression m)

        {

            if (_projection)

                return null;



            List<Object> args = this.VisitExpressionList(m.Arguments);

            var quotedColName = (MemberAccessString)Visit(m.Object);

            quotedColName.Text = _projection ? _databaseType.EscapeSqlIdentifier(quotedColName.PocoColumn.AutoAlias) : quotedColName.Text;

            string statement;



            switch (m.Method.Name)

            {

                case "ToUpper":

                    statement = string.Format("upper({0})", quotedColName);

                    break;

                case "ToLower":

                    statement = string.Format("lower({0})", quotedColName);

                    break;

                case "StartsWith":

                    statement = string.Format("upper({0}) like {1}", quotedColName, CreateParam(args[0].ToString().ToUpper() + "%"));

                    break;

                case "EndsWith":

                    statement = string.Format("upper({0}) like {1}", quotedColName, CreateParam("%" + args[0].ToString().ToUpper()));

                    break;

                case "Contains":

                    statement = string.Format("upper({0}) like {1}", quotedColName, CreateParam("%" + args[0].ToString().ToUpper() + "%"));

                    break;

                case "Substring":

                    var startIndex = Int32.Parse(args[0].ToString()) + 1;

                    if (args.Count == 2)

                    {

                        var length = Int32.Parse(args[1].ToString());

                        statement = string.Format("substring({0},{1},{2})", quotedColName, startIndex, length);

                    }

                    else

                        statement = string.Format("substring({0},{1},8000)", quotedColName, startIndex);

                    break;

                case "Equals":

                    statement = string.Format("({0} = {1})", quotedColName, args[0]);

                    break;

                case "ToString":

                    statement = string.Empty;

                    break;

                default:

                    throw new NotSupportedException();

            }



            quotedColName.Text = statement;

            return quotedColName;

        }

    }



    public class PartialSqlString

    {

        public PartialSqlString(string text)

        {

            Text = text;

        }

        public string Text { get; set; }

        public override string ToString()

        {

            return Text;

        }

    }



    public class MemberAccessString : PartialSqlString

    {

        public MemberAccessString(PocoColumn pocoColumn, string text, Type type) 

            : base(text)

        {

            PocoColumn = pocoColumn;

            Type = type;

        }



        public PocoColumn PocoColumn { get; private set; }

        public Type Type { get; set; }

    }



    public class NullableMemberAccess : MemberAccessString

    {

        public NullableMemberAccess(PocoColumn pocoColumn, string text, Type type) : base(pocoColumn, text, type)

        {

        }

    }



    public class EnumMemberAccess : MemberAccessString

    {

        public EnumMemberAccess(PocoColumn pocoColumn, string text, Type type) : base(pocoColumn, text, type)

        {

        }

    }



    public static class LinqExtensions

    {

        /// <summary>

        /// Gets the constant value.

        /// </summary>

        /// <param retval="exp">The exp.</param>

        /// <returns>The get constant value.</returns>

        public static T GetConstantValue<T>(this Expression exp)

        {

            T result = default(T);

            if (exp is ConstantExpression)

            {

                var c = (ConstantExpression)exp;



                result = (T)c.Value;

            }



            return result;

        }

    }



}