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// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
namespace System.Web.Http.Query
{
// TODO: ability to extend the composer. Bug 322919
/// <summary>
/// Used to compose two separate queries into a single query
/// </summary>
internal static class QueryComposer
{
/// <summary>
/// Composes the specified query with the source provided.
/// </summary>
/// <param name="source">The root or source query</param>
/// <param name="query">The query to compose</param>
/// <returns>The composed query</returns>
public static IQueryable Compose(IQueryable source, IQueryable query)
{
return QueryRebaser.Rebase(source, query);
}
/// <summary>
/// Class used to insert a specified query source into another separate
/// query, effectively "rebasing" the query source.
/// </summary>
public class QueryRebaser : ExpressionVisitor
{
/// <summary>
/// Rebase the specified query to the specified source
/// </summary>
/// <param name="source">The query source</param>
/// <param name="query">The query to rebase</param>
/// <returns>Returns the edited query.</returns>
public static IQueryable Rebase(IQueryable source, IQueryable query)
{
Visitor v = new Visitor(source.Expression);
Expression expr = v.Visit(query.Expression);
return source.Provider.CreateQuery(expr);
}
private class Visitor : ExpressionVisitor
{
private Expression _root;
public Visitor(Expression root)
{
_root = root;
}
protected override Expression VisitMethodCall(MethodCallExpression m)
{
if ((m.Arguments.Count > 0 && m.Arguments[0].NodeType == ExpressionType.Constant) &&
(((ConstantExpression)m.Arguments[0]).Value != null) &&
(((ConstantExpression)m.Arguments[0]).Value is IQueryable))
{
// we found the innermost source which we replace with the
// specified source
List<Expression> exprs = new List<Expression>();
exprs.Add(_root);
exprs.AddRange(m.Arguments.Skip(1));
return Expression.Call(m.Method, exprs.ToArray());
}
return base.VisitMethodCall(m);
}
}
}
}
}
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