Line data    Source code

       1             : #region Copyright
       2             : // // -----------------------------------------------------------------------
       3             : // // <copyright company="Chinchilla Software Limited">
       4             : // //   Copyright Chinchilla Software Limited. All rights reserved.
       5             : // // </copyright>
       6             : // // -----------------------------------------------------------------------
       7             : #endregion
       8             : 
       9             : using System;
      10             : using System.Collections.Generic;
      11             : using System.Linq;
      12             : using System.Linq.Expressions;
      13             : using System.Reflection;
      14             : 
      15             : namespace Cqrs.Sql.DataStores
      16             : {
      17             :         /// <summary>
      18             :         /// Converts <see cref="Expression"/> trees.
      19             :         /// </summary>
      20             :         public abstract class ExpressionTreeConverter<TA, TB> : ExpressionVisitor, IExpressionTreeConverter
      21           1 :         {
      22             :                 private readonly Dictionary<ParameterExpression, ParameterExpression> _parameters = new Dictionary<ParameterExpression, ParameterExpression>();
      23             : 
      24             :                 private readonly Dictionary<MemberInfo, LambdaExpression> _mappings;
      25             : 
      26             :                 /// <summary>
      27             :                 /// Instantiates a new instance of the <see cref="ExpressionTreeConverter{TA,TB}"/> class
      28             :                 /// </summary>
      29           1 :                 protected ExpressionTreeConverter(Dictionary<MemberInfo, LambdaExpression> mappings)
      30             :                 {
      31             :                         _mappings = mappings;
      32             :                 }
      33             : 
      34             :                 /// <summary>
      35             :                 /// Instantiates a new instance of the <see cref="ExpressionTreeConverter{TA,TB}"/> class
      36             :                 /// </summary>
      37           1 :                 protected ExpressionTreeConverter()
      38             :                 {
      39             :                         _mappings = GetMappings();
      40             :                 }
      41             : 
      42             :                 /// <summary>
      43             :                 /// A collection of <see cref="LambdaExpression"/> grouped by <see cref="MemberInfo"/>.
      44             :                 /// </summary>
      45           1 :                 public abstract Dictionary<MemberInfo, LambdaExpression> GetMappings();
      46             : 
      47             :                 /// <summary>
      48             :                 /// If the <paramref name="node"/> if of <see cref="Type"/> <typeparamref name="TA"/>
      49             :                 /// A <see cref="ParameterExpression"/> of <see cref="Type"/> <typeparamref name="TB"/> will to created with the same name.
      50             :                 /// </summary>
      51           1 :                 protected override Expression VisitParameter(ParameterExpression node)
      52             :                 {
      53             :                         if (node.Type == typeof(TA))
      54             :                         {
      55             :                                 ParameterExpression parameter;
      56             :                                 if (!_parameters.TryGetValue(node, out parameter))
      57             :                                 {
      58             :                                         _parameters.Add(node, parameter = Expression.Parameter(typeof(TB), node.Name));
      59             :                                 }
      60             :                                 return parameter;
      61             :                         }
      62             :                         return node;
      63             :                 }
      64             : 
      65             :                 /// <summary>
      66             :                 /// If the <see cref="MemberExpression.Member"/> of the provided <paramref name="node"/> matches a mapping in 
      67             :                 /// <see cref="GetMappings"/>, then that mapping is executed.
      68             :                 /// </summary>
      69           1 :                 protected override Expression VisitMember(MemberExpression node)
      70             :                 {
      71             :                         if (node.Expression == null || node.Expression.Type != typeof(TA))
      72             :                                 return base.VisitMember(node);
      73             : 
      74             :                         Expression expression = Visit(node.Expression);
      75             :                         if (expression.Type != typeof(TB))
      76             :                                 throw new Exception("Whoops");
      77             : 
      78             :                         LambdaExpression lambdaExpression;
      79             :                         if (_mappings.TryGetValue(node.Member, out lambdaExpression))
      80             :                                 return new SimpleExpressionReplacer(lambdaExpression.Parameters.Single(), expression).Visit(lambdaExpression.Body);
      81             : 
      82             :                         return Expression.Property(expression, node.Member.Name);
      83             :                 }
      84             : 
      85             :                 /// <summary>
      86             :                 /// Visits the children of the <paramref name="node"/>.
      87             :                 /// </summary>
      88           1 :                 protected override Expression VisitLambda<T>(Expression<T> node)
      89             :                 {
      90             :                         return Expression.Lambda(
      91             :                                 Visit(node.Body),
      92             :                                 node.Parameters.Select(Visit).Cast<ParameterExpression>()
      93             :                                 );
      94             :                 }
      95             :         }
      96             : }