//Copyright 2010 Microsoft Corporation
//
//Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
//You may obtain a copy of the License at
//
//http://www.apache.org/licenses/LICENSE-2.0
//
//Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an
//"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//See the License for the specific language governing permissions and limitations under the License.
namespace System.Data.Services.Client{
#region Namespaces.
using System;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;
#endregion Namespaces.
internal class ProjectionRewriter : ExpressionVisitor
{
#region Private fields.
private readonly ParameterExpression newLambdaParameter;
private ParameterExpression oldLambdaParameter;
private bool sucessfulRebind;
#endregion Private fields.
private ProjectionRewriter(Type proposedParameterType)
{
Debug.Assert(proposedParameterType != null, "proposedParameterType != null");
this.newLambdaParameter = Expression.Parameter(proposedParameterType, "it");
}
#region Internal methods.
internal static LambdaExpression TryToRewrite(LambdaExpression le, Type proposedParameterType)
{
LambdaExpression result;
if (!ResourceBinder.PatternRules.MatchSingleArgumentLambda(le, out le) || ClientType.CheckElementTypeIsEntity(le.Parameters[0].Type) || !(le.Parameters[0].Type.GetProperties().Any(p => p.PropertyType == proposedParameterType))) {
result = le;
}
else
{
ProjectionRewriter rewriter = new ProjectionRewriter(proposedParameterType);
result = rewriter.Rebind(le);
}
return result;
}
internal LambdaExpression Rebind(LambdaExpression lambda)
{
this.sucessfulRebind = true;
this.oldLambdaParameter = lambda.Parameters[0];
Expression body = this.Visit(lambda.Body);
if (this.sucessfulRebind)
{
Type delegateType = typeof(Func<,>).MakeGenericType(new Type[] { newLambdaParameter.Type, lambda.Body.Type });
#if ASTORIA_LIGHT
return ExpressionHelpers.CreateLambda(delegateType, body, new ParameterExpression[] { this.newLambdaParameter });
#else
return Expression.Lambda(delegateType, body, new ParameterExpression[] { this.newLambdaParameter });
#endif
}
else
{
throw new NotSupportedException(Strings.ALinq_CanOnlyProjectTheLeaf);
}
}
internal override Expression VisitMemberAccess(MemberExpression m)
{
if (m.Expression == this.oldLambdaParameter)
{
if (m.Type == this.newLambdaParameter.Type)
{
return this.newLambdaParameter;
}
else
{
this.sucessfulRebind = false;
}
}
return base.VisitMemberAccess(m);
}
#endregion Internal methods.
}
}
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