/BlogEngine/DotNetSlave.BusinessLogic/Compilation/LinqLengthExpressionBuilder.cs

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

// <summary>

//   Linq Length Expression Builder

// </summary>

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



namespace BlogEngine.Core.Compilation

{

    using System;

    using System.CodeDom;

    using System.Data.Linq.Mapping;

    using System.Linq;

    using System.Web.Compilation;

    using System.Web.UI;



    /// <summary>

    /// Linq Length Expression Builder

    /// </summary>

    /// <remarks>

    /// The example usage below uses an Employee table with a Name column. Employee may need to be namespace referenced

    ///     like improvGroup.Manager.Data.Employee if the namespace of the page is different than the data entity namespace.

    /// </remarks>

    /// <example>

    /// &lt;asp:TextBox ID="TextBoxName" runat="server" MaxLength='&lt;%$LinqLength:Employee.Name%&gt;' /&gt;

    /// </example>

    [ExpressionPrefix("LinqLength")]

    public class LinqLengthExpressionBuilder : ExpressionBuilder

    {

        #region Public Methods



        /// <summary>

        /// Gets the code expression.

        /// </summary>

        /// <param name="entry">

        /// The entry.

        /// </param>

        /// <param name="parsedData">

        /// The parsed data.

        /// </param>

        /// <param name="context">

        /// The context.

        /// </param>

        /// <returns>

        /// A CodeExpression.

        /// </returns>

        public override CodeExpression GetCodeExpression(

            BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context)

        {

            var typeName = BeforeLast(entry.Expression, ".");

            var propertyName = AfterLast(entry.Expression, ".");



            return new CodePrimitiveExpression(PropertyLength(typeName, propertyName));

        }



        #endregion



        #region Methods



        /// <summary>

        /// Gets the end of the string after the last instance of the last.

        /// </summary>

        /// <param name="value">

        /// The string value.

        /// </param>

        /// <param name="last">

        /// The value to search for.

        /// </param>

        /// <returns>

        /// The string after the last instance of last.

        /// </returns>

        private static string AfterLast(string value, string last)

        {

            if (value == null)

            {

                throw new ArgumentNullException("value");

            }



            return value.Substring(value.LastIndexOf(last) + last.Length);

        }



        /// <summary>

        /// Get the string up to the last instance of last.

        /// </summary>

        /// <param name="value">

        /// The string value.

        /// </param>

        /// <param name="last">

        /// The instance to search for the last of.

        /// </param>

        /// <returns>

        /// The string up to the last instance of last.

        /// </returns>

        private static string BeforeLast(string value, string last)

        {

            if (value == null)

            {

                throw new ArgumentNullException("value");

            }



            if (last == null)

            {

                throw new ArgumentNullException("last");

            }



            return value.Substring(0, value.LastIndexOf(last));

        }



        /// <summary>

        /// Gets the string value between the start and the end.

        /// </summary>

        /// <param name="value">

        /// The value to search.

        /// </param>

        /// <param name="startText">

        /// The start text to skip.

        /// </param>

        /// <param name="endText">

        /// The end text to skip.

        /// </param>

        /// <returns>

        /// The middle of the string between start and end.

        /// </returns>

        private static string BetweenFirst(string value, string startText, string endText)

        {

            if (value == null)

            {

                throw new ArgumentNullException("value");

            }



            var start = value.IndexOf(startText, StringComparison.OrdinalIgnoreCase) + startText.Length;

            var end = value.IndexOf(endText, start, StringComparison.OrdinalIgnoreCase);



            return value.Substring(start, end - start);

        }



        /// <summary>

        /// Gets the length of the property.

        /// </summary>

        /// <param name="typeName">

        /// Name of the type.

        /// </param>

        /// <param name="propertyName">

        /// Name of the property.

        /// </param>

        /// <returns>

        /// The length of the property.

        /// </returns>

        private static int PropertyLength(string typeName, string propertyName)

        {

            var attribute =

                (ColumnAttribute)

                BuildManager.GetType(typeName, true).GetProperty(propertyName).GetCustomAttributes(

                    typeof(ColumnAttribute), false).Single();

                

                // <-- look, I just had to use a tiny bit of LINQ in this code!

            return int.Parse(BetweenFirst(attribute.DbType, "char(", ")"));

        }



        #endregion

    }

}