NH-3499 - Allow custom QueryModelVisitorBase to be provided through the session factory

Implements a new parameter on the session factory to provide a IQueryModelRewriterFactory which is used in QueryModelVisitor to allow the query model to be rewritten.

Author: pvginkel

src/NHibernate.Test/Linq/CustomQueryModelRewriterTests.cs

@@ -0,0 +1,91 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using NHibernate.Linq.Visitors;
+using NUnit.Framework;
+using Remotion.Linq;
+using Remotion.Linq.Clauses;
+using Remotion.Linq.Parsing;
+using SharpTestsEx;
+
+namespace NHibernate.Test.Linq
+{
+	public class CustomQueryModelRewriterTests : LinqTestCase
+	{
+		protected override void Configure(Cfg.Configuration configuration)
+		{
+			configuration.Properties[Cfg.Environment.QueryModelRewriterFactory] = typeof(QueryModelRewriterFactory).AssemblyQualifiedName;
+		}
+
+		[Test]
+		public void RewriteNullComparison()
+		{
+			// This example shows how to use the query model rewriter to
+			// make radical changes to the query. In this case, we rewrite
+			// a null comparison (which would translate into a IS NULL)
+			// into a comparison to "Thomas Hardy" (which translates to a = "Thomas Hardy").
+
+			var contacts = (from c in db.Customers where c.ContactName == null select c).ToList();
+			contacts.Count.Should().Be.GreaterThan(0);
+			contacts.Select(customer => customer.ContactName).All(c => c.Satisfy(customer => customer == "Thomas Hardy"));
+		}
+
+		[Serializable]
+		public class QueryModelRewriterFactory : IQueryModelRewriterFactory
+		{
+			public QueryModelVisitorBase CreateVisitor(VisitorParameters parameters)
+			{
+				return new CustomVisitor();
+			}
+		}
+
+		public class CustomVisitor : QueryModelVisitorBase
+		{
+			public override void VisitWhereClause(WhereClause whereClause, QueryModel queryModel, int index)
+			{
+				whereClause.TransformExpressions(new Visitor().VisitExpression);
+			}
+
+			private class Visitor : ExpressionTreeVisitor
+			{
+				protected override Expression VisitBinaryExpression(BinaryExpression expression)
+				{
+					if (
+						expression.NodeType == ExpressionType.Equal ||
+						expression.NodeType == ExpressionType.NotEqual
+					)
+					{
+						var left = expression.Left;
+						var right = expression.Right;
+						bool reverse = false;
+
+						if (!(left is ConstantExpression) && right is ConstantExpression)
+						{
+							var tmp = left;
+							left = right;
+							right = tmp;
+							reverse = true;
+						}
+
+						var constant = left as ConstantExpression;
+
+						if (constant != null && constant.Value == null)
+						{
+							left = Expression.Constant("Thomas Hardy");
+
+							expression = Expression.MakeBinary(
+								expression.NodeType,
+								reverse ? right : left,
+								reverse ? left : right
+							);
+						}
+					}
+
+					return base.VisitBinaryExpression(expression);
+				}
+			}
+		}
+	}
+}

src/NHibernate.Test/NHibernate.Test.csproj

@@ -80,6 +80,10 @@
       <SpecificVersion>False</SpecificVersion>
       <HintPath>..\..\lib\net\nunit.framework.dll</HintPath>
     </Reference>
+    <Reference Include="Remotion.Linq, Version=1.13.171.1, Culture=neutral, PublicKeyToken=fee00910d6e5f53b, processorArchitecture=MSIL">
+      <SpecificVersion>False</SpecificVersion>
+      <HintPath>..\..\lib\net\Remotion.Linq.dll</HintPath>
+    </Reference>
     <Reference Include="SharpTestsEx.NUnit, Version=1.0.0.0, Culture=neutral, PublicKeyToken=8c60d8070630b1c1, processorArchitecture=MSIL">
       <SpecificVersion>False</SpecificVersion>
       <HintPath>..\..\lib\net\SharpTestsEx.NUnit.dll</HintPath>
@@ -507,6 +511,7 @@
     <Compile Include="Linq\ByMethod\GetValueOrDefaultTests.cs" />
     <Compile Include="Linq\CasingTest.cs" />
     <Compile Include="Linq\CharComparisonTests.cs" />
+    <Compile Include="Linq\CustomQueryModelRewriterTests.cs" />
     <Compile Include="Linq\DateTimeTests.cs" />
     <Compile Include="Linq\LoggingTests.cs" />
     <Compile Include="Linq\QueryTimeoutTests.cs" />

src/NHibernate/Cfg/Environment.cs

@@ -171,6 +171,8 @@ public static string Version
 		/// <summary> Enable ordering of insert statements for the purpose of more effecient batching.</summary>
 		public const string OrderInserts = "order_inserts";
 
+		public const string QueryModelRewriterFactory = "query.query_model_rewriter_factory";
+
 		private static readonly Dictionary<string, string> GlobalProperties;
 
 		private static IBytecodeProvider BytecodeProviderInstance;

src/NHibernate/Cfg/Settings.cs

@@ -7,6 +7,7 @@
 using NHibernate.Exceptions;
 using NHibernate.Hql;
 using NHibernate.Linq.Functions;
+using NHibernate.Linq.Visitors;
 using NHibernate.Transaction;
 
 namespace NHibernate.Cfg
@@ -125,6 +126,8 @@ public Settings()
 		/// </summary>
 		public ILinqToHqlGeneratorsRegistry LinqToHqlGeneratorsRegistry { get; internal set; }
 
+		public IQueryModelRewriterFactory QueryModelRewriterFactory { get; internal set; }
+		
 		#endregion
 	}
 }

src/NHibernate/Cfg/SettingsFactory.cs

@@ -11,6 +11,7 @@
 using NHibernate.Exceptions;
 using NHibernate.Hql;
 using NHibernate.Linq.Functions;
+using NHibernate.Linq.Visitors;
 using NHibernate.Transaction;
 using NHibernate.Util;
 
@@ -280,8 +281,10 @@ public Settings BuildSettings(IDictionary<string, string> properties)
 			settings.IsSecondLevelCacheEnabled = useSecondLevelCache;
 			settings.CacheRegionPrefix = cacheRegionPrefix;
 			settings.IsMinimalPutsEnabled = useMinimalPuts;
-			// Not ported - JdbcBatchVersionedData
-
+			// Not ported - JdbcBatchVersionedData
+
+			settings.QueryModelRewriterFactory = CreateQueryModelRewriterFactory(properties);
+			
 			// NHibernate-specific:
 			settings.IsolationLevel = isolation;
 
@@ -373,5 +376,26 @@ private static ITransactionFactory CreateTransactionFactory(IDictionary<string,
 				throw new HibernateException("could not instantiate TransactionFactory: " + className, cnfe);
 			}
 		}
+
+		private static IQueryModelRewriterFactory CreateQueryModelRewriterFactory(IDictionary<string, string> properties)
+		{
+			string className = PropertiesHelper.GetString(Environment.QueryModelRewriterFactory, properties, null);
+
+			if (className == null)
+				return null;
+
+			log.Info("Query model rewriter factory factory: " + className);
+
+			try
+			{
+				return
+					(IQueryModelRewriterFactory)
+					Environment.BytecodeProvider.ObjectsFactory.CreateInstance(ReflectHelper.ClassForName(className));
+			}
+			catch (Exception cnfe)
+			{
+				throw new HibernateException("could not instantiate IQueryModelRewriterFactory: " + className, cnfe);
+			}
+		}
 	}
 }

src/NHibernate/Linq/Visitors/IQueryModelRewriterFactory.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Remotion.Linq;
+
+namespace NHibernate.Linq.Visitors
+{
+	public interface IQueryModelRewriterFactory
+	{
+		QueryModelVisitorBase CreateVisitor(VisitorParameters parameters);
+	}
+}

src/NHibernate/Linq/Visitors/QueryModelVisitor.cs

@@ -57,6 +57,16 @@ public static ExpressionToHqlTranslationResults GenerateHqlQuery(QueryModel quer
 			// Move OrderBy clauses to end
 			MoveOrderByToEndRewriter.ReWrite(queryModel);
 
+			// Give a rewriter provided by the session factory a chance to
+			// rewrite the query.
+			var rewriterFactory = parameters.SessionFactory.Settings.QueryModelRewriterFactory;
+			if (rewriterFactory != null)
+			{
+				var customVisitor = rewriterFactory.CreateVisitor(parameters);
+				if (customVisitor != null)
+					customVisitor.VisitQueryModel(queryModel);
+			}
+
 			// rewrite any operators that should be applied on the outer query
 			// by flattening out the sub-queries that they are located in
 			var result = ResultOperatorRewriter.Rewrite(queryModel);

src/NHibernate/NHibernate.csproj

@@ -296,6 +296,7 @@
     <Compile Include="Linq\NestedSelects\Tuple.cs" />
     <Compile Include="Linq\NestedSelects\SelectClauseRewriter.cs" />
     <Compile Include="Linq\NestedSelects\ExpressionHolder.cs" />
+    <Compile Include="Linq\Visitors\IQueryModelRewriterFactory.cs" />
     <Compile Include="Linq\Visitors\LeftJoinRewriter.cs" />
     <Compile Include="Linq\Functions\CompareGenerator.cs" />
     <Compile Include="Linq\ExpressionTransformers\SimplifyCompareTransformer.cs" />