/BlogEngine/DotNetSlave.BusinessLogic/Compilation/BaseServerObjectExpressionBuilder.cs

// --------------------------------------------------------------------------------------------------------------------

// <summary>

//   Base Server Object Expression Builder

// </summary>

// --------------------------------------------------------------------------------------------------------------------



namespace BlogEngine.Core.Compilation

{

    using System;

    using System.CodeDom;

    using System.ComponentModel;

    using System.Web;

    using System.Web.Compilation;

    using System.Web.UI;



    /// <summary>

    /// Base Server Object Expression Builder

    /// </summary>

    public abstract class BaseServerObjectExpressionBuilder : ExpressionBuilder

    {

        #region Properties



        /// <summary>

        ///     Gets the name of the source object.

        /// </summary>

        /// <value>The name of the source object.</value>

        public abstract string SourceObjectName { get; }



        /// <summary>

        ///     When overridden in a derived class, returns a value indicating whether the current <see cref = "T:System.Web.Compilation.ExpressionBuilder" /> object supports no-compile pages.

        /// </summary>

        /// <value></value>

        /// <returns>true if the <see cref = "T:System.Web.Compilation.ExpressionBuilder" /> supports expression evaluation; otherwise, false.

        /// </returns>

        public override bool SupportsEvaluate

        {

            get

            {

                return true;

            }

        }



        #endregion



        #region Public Methods



        /// <summary>

        /// When overridden in a derived class, returns an object that represents an evaluated expression.

        /// </summary>

        /// <param name="target">

        /// The object containing the expression.

        /// </param>

        /// <param name="entry">

        /// The object that represents information about the property bound to by the expression.

        /// </param>

        /// <param name="parsedData">

        /// The object containing parsed data as returned by <see cref="M:System.Web.Compilation.ExpressionBuilder.ParseExpression(System.String,System.Type,System.Web.Compilation.ExpressionBuilderContext)"/>.

        /// </param>

        /// <param name="context">

        /// Contextual information for the evaluation of the expression.

        /// </param>

        /// <returns>

        /// An object that represents the evaluated expression; otherwise, null if the inheritor does not implement <see cref="M:System.Web.Compilation.ExpressionBuilder.EvaluateExpression(System.Object,System.Web.UI.BoundPropertyEntry,System.Object,System.Web.Compilation.ExpressionBuilderContext)"/>.

        /// </returns>

        public override object EvaluateExpression(

            object target, BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context)

        {

            return this.GetRequestedValue(entry.Expression.Trim(), target.GetType(), entry.PropertyInfo.Name);

        }



        /// <summary>

        /// When overridden in a derived class, returns code that is used during page execution to obtain the evaluated expression.

        /// </summary>

        /// <param name="entry">

        /// The object that represents information about the property bound to by the expression.

        /// </param>

        /// <param name="parsedData">

        /// The object containing parsed data as returned by <see cref="M:System.Web.Compilation.ExpressionBuilder.ParseExpression(System.String,System.Type,System.Web.Compilation.ExpressionBuilderContext)"/>.

        /// </param>

        /// <param name="context">

        /// Contextual information for the evaluation of the expression.

        /// </param>

        /// <returns>

        /// A <see cref="T:System.CodeDom.CodeExpression"/> that is used for property assignment.

        /// </returns>

        public override CodeExpression GetCodeExpression(

            BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context)

        {

            var inputParams = new CodeExpression[]

                {

                    new CodePrimitiveExpression(entry.Expression.Trim()), new CodeTypeOfExpression(entry.DeclaringType), 

                    new CodePrimitiveExpression(entry.PropertyInfo.Name)

                };



            // Return a CodeMethodInvokeExpression that will invoke the GetRequestedValue method using the specified input parameters

            return new CodeMethodInvokeExpression(

                new CodeTypeReferenceExpression(this.GetType()), "Instance().GetRequestedValue", inputParams);

        }



        /// <summary>

        /// Gets the requested value.

        /// </summary>

        /// <param name="key">

        /// The key of the requested value.

        /// </param>

        /// <param name="targetType">

        /// Type of the target.

        /// </param>

        /// <param name="propertyName">

        /// Name of the property.

        /// </param>

        /// <returns>

        /// The requested value.

        /// </returns>

        public object GetRequestedValue(string key, Type targetType, string propertyName)

        {

            // First make sure that the server object will be available

            if (HttpContext.Current == null)

            {

                return null;

            }



            // Get the value

            var value = this.GetValue(key);



            // Make sure that the value exists

            if (value == null)

            {

                throw new InvalidOperationException(

                    string.Format("{0} field '{1}' not found.", this.SourceObjectName, key));

            }



            // If the value is being assigned to a control property we may need to convert it

            if (targetType != null)

            {

                var propDesc = TypeDescriptor.GetProperties(targetType)[propertyName];



                // Type mismatch - make sure that the value can be converted

                if (propDesc != null && propDesc.PropertyType != value.GetType() && propDesc.Converter != null)

                {

                    if (propDesc.Converter.CanConvertFrom(value.GetType()) == false)

                    {

                        throw new InvalidOperationException(

                            string.Format(

                                "{0} value '{1}' cannot be converted to type {2}.",

                                this.SourceObjectName,

                                key,

                                propDesc.PropertyType));

                    }



                    return propDesc.Converter.ConvertFrom(value);

                }

            }



            // If we reach here, no type mismatch - return the value

            return value;

        }



        #endregion



        #region Methods



        /// <summary>

        /// Gets the value.

        /// </summary>

        /// <param name="key">

        /// The key of the value to retrieve.

        /// </param>

        /// <returns>

        /// The value.

        /// </returns>

        protected abstract object GetValue(string key);



        #endregion

    }

}