Port Hibernate's support subqueries in HQL as CASE statement alternatives

src/NHibernate.Test/Async/Hql/SubQueryTest.cs

@@ -0,0 +1,70 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+
+namespace NHibernate.Test.Hql
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class SubQueryTestAsync : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Root>(
+				rc =>
+				{
+					rc.Id(x => x.Id, m => m.Generator(Generators.Native));
+					rc.Property(x => x.RootName);
+					rc.ManyToOne(x => x.Branch);
+				});
+
+			mapper.Class<Branch>(
+				rc =>
+				{
+					rc.Id(x => x.Id, m => m.Generator(Generators.Native));
+					rc.Property(x => x.BranchName);
+					rc.Bag(x => x.Leafs, cm => cm.Cascade(Mapping.ByCode.Cascade.All), x => x.OneToMany());
+				});
+			mapper.Class<Leaf>(
+				rc =>
+				{
+					rc.Id(x => x.Id, m => m.Generator(Generators.Native));
+					rc.Property(x => x.LeafName);
+				});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override bool AppliesTo(Dialect.Dialect dialect)
+		{
+			return dialect.SupportsScalarSubSelects;
+		}
+
+		[TestCase("SELECT CASE WHEN l.id IS NOT NULL THEN (SELECT COUNT(r.id) FROM Root r) ELSE 0 END FROM Leaf l")]
+		[TestCase("SELECT CASE WHEN (SELECT COUNT(r.id) FROM Root r) > 1 THEN 1 ELSE 0 END FROM Leaf l")]
+		[TestCase("SELECT CASE WHEN  l.id > 1 THEN 1 ELSE (SELECT COUNT(r.id) FROM Root r) END FROM Leaf l")]
+		[TestCase("SELECT CASE (SELECT COUNT(r.id) FROM Root r) WHEN  1 THEN 1 ELSE 0 END FROM Leaf l")]
+		[TestCase("SELECT CASE l.id WHEN (SELECT COUNT(r.id) FROM Root r) THEN 1 ELSE 0 END FROM Leaf l")]
+		public async Task TestSubQueryAsync(string query)
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				// Simple syntax check
+				await (session.CreateQuery(query).ListAsync());
+				await (transaction.CommitAsync());
+			}
+		}
+	}
+}

src/NHibernate.Test/Async/NHSpecificTest/GH1879/FixtureByCode.cs

@@ -12,6 +12,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using NHibernate.Cfg.MappingSchema;
+using NHibernate.Exceptions;
 using NHibernate.Mapping.ByCode;
 using NHibernate.Type;
 using NUnit.Framework;
@@ -124,8 +125,7 @@ protected async Task AreEqualAsync<TResult>(
 				{
 					expectedResult = await (expectedQuery(session.Query<T>()).ToListAsync(cancellationToken));
 				}
-				catch (OperationCanceledException) { throw; }
-				catch (Exception e)
+				catch (GenericADOException e)
 				{
 					Assert.Ignore($"Not currently supported query: {e}");
 				}

src/NHibernate.Test/Hql/Ast/SqlTranslationFixture.cs

@@ -23,6 +23,16 @@ public void CaseClauseWithMath()
 			Assert.DoesNotThrow(() => GetSql(queryWithoutParen));
 		}
 
+		[Test]
+		public void SimpleCaseClauseWithMath()
+		{
+			const string query = "from SimpleClass s where (case (cast(s.IntValue as long) * :pAValue) when (cast(s.IntValue as long) * :pAValue) then (cast(s.IntValue as long) * :pAValue) else 1 end) > 0";
+			Assert.DoesNotThrow(() => GetSql(query));
+
+			const string queryWithoutParen = "from SimpleClass s where (case cast(s.IntValue as long) * :pAValue when cast(s.IntValue as long) * :pAValue then cast(s.IntValue as long) * :pAValue else 1 end) > 0";
+			Assert.DoesNotThrow(() => GetSql(queryWithoutParen));
+		}
+
 		[Test]
 		public void Union()
 		{

src/NHibernate.Test/Hql/SubQueryTest.cs

@@ -0,0 +1,59 @@
+using NHibernate.Cfg.MappingSchema;
+using NHibernate.Mapping.ByCode;
+using NUnit.Framework;
+
+namespace NHibernate.Test.Hql
+{
+	[TestFixture]
+	public class SubQueryTest : TestCaseMappingByCode
+	{
+		protected override HbmMapping GetMappings()
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Root>(
+				rc =>
+				{
+					rc.Id(x => x.Id, m => m.Generator(Generators.Native));
+					rc.Property(x => x.RootName);
+					rc.ManyToOne(x => x.Branch);
+				});
+
+			mapper.Class<Branch>(
+				rc =>
+				{
+					rc.Id(x => x.Id, m => m.Generator(Generators.Native));
+					rc.Property(x => x.BranchName);
+					rc.Bag(x => x.Leafs, cm => cm.Cascade(Mapping.ByCode.Cascade.All), x => x.OneToMany());
+				});
+			mapper.Class<Leaf>(
+				rc =>
+				{
+					rc.Id(x => x.Id, m => m.Generator(Generators.Native));
+					rc.Property(x => x.LeafName);
+				});
+
+			return mapper.CompileMappingForAllExplicitlyAddedEntities();
+		}
+
+		protected override bool AppliesTo(Dialect.Dialect dialect)
+		{
+			return dialect.SupportsScalarSubSelects;
+		}
+
+		[TestCase("SELECT CASE WHEN l.id IS NOT NULL THEN (SELECT COUNT(r.id) FROM Root r) ELSE 0 END FROM Leaf l")]
+		[TestCase("SELECT CASE WHEN (SELECT COUNT(r.id) FROM Root r) > 1 THEN 1 ELSE 0 END FROM Leaf l")]
+		[TestCase("SELECT CASE WHEN  l.id > 1 THEN 1 ELSE (SELECT COUNT(r.id) FROM Root r) END FROM Leaf l")]
+		[TestCase("SELECT CASE (SELECT COUNT(r.id) FROM Root r) WHEN  1 THEN 1 ELSE 0 END FROM Leaf l")]
+		[TestCase("SELECT CASE l.id WHEN (SELECT COUNT(r.id) FROM Root r) THEN 1 ELSE 0 END FROM Leaf l")]
+		public void TestSubQuery(string query)
+		{
+			using (var session = OpenSession())
+			using (var transaction = session.BeginTransaction())
+			{
+				// Simple syntax check
+				session.CreateQuery(query).List();
+				transaction.Commit();
+			}
+		}
+	}
+}

src/NHibernate.Test/Hql/SubQueryTestEntities.cs

@@ -0,0 +1,29 @@
+using System.Collections.Generic;
+
+namespace NHibernate.Test.Hql
+{
+	public class Root
+	{
+		public virtual int Id { get; set; }
+
+		public virtual string RootName { get; set; }
+
+		public virtual Branch Branch { get; set; }
+	}
+
+	public class Branch
+	{
+		public virtual int Id { get; set; }
+
+		public virtual string BranchName { get; set; }
+
+		public virtual IList<Leaf> Leafs { get; set; }
+	}
+
+	public class Leaf
+	{
+		public virtual int Id { get; set; }
+
+		public virtual string LeafName { get; set; }
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH1879/FixtureByCode.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using NHibernate.Cfg.MappingSchema;
+using NHibernate.Exceptions;
 using NHibernate.Mapping.ByCode;
 using NHibernate.Type;
 using NUnit.Framework;
@@ -111,7 +112,7 @@ protected void AreEqual<TResult>(
 				{
 					expectedResult = expectedQuery(session.Query<T>()).ToList();
 				}
-				catch (Exception e)
+				catch (GenericADOException e)
 				{
 					Assert.Ignore($"Not currently supported query: {e}");
 				}

src/NHibernate/Hql/Ast/ANTLR/Hql.g

@@ -527,23 +527,31 @@ unaryExpression
 	;
 
 caseExpression
-	: CASE (whenClause)+ (elseClause)? END
-		-> ^(CASE whenClause+ elseClause?) 
-	| CASE unaryExpression (altWhenClause)+ (elseClause)? END
-		-> ^(CASE2 unaryExpression altWhenClause+ elseClause?)
+	: simpleCaseStatement
+	| searchedCaseStatement
 	;
-
-whenClause
-	: (WHEN^ logicalExpression THEN! expression)
+
+simpleCaseStatement
+	: CASE expression (simpleCaseWhenClause)+ (elseClause)? END
+		-> ^(CASE2 expression simpleCaseWhenClause+ elseClause?)
 	;
-	
-altWhenClause
-	: (WHEN^ unaryExpression THEN! expression)
+
+simpleCaseWhenClause
+	: (WHEN^ expression THEN! expression)
 	;
 
 elseClause
 	: (ELSE^ expression)
 	;
+
+searchedCaseStatement
+	: CASE (searchedCaseWhenClause)+ (elseClause)? END
+		-> ^(CASE searchedCaseWhenClause+ elseClause?)
+	;
+
+searchedCaseWhenClause
+	: (WHEN^ logicalExpression THEN! expression)
+	;
 
 quantifiedExpression
 	: ( SOME^ | EXISTS^ | ALL^ | ANY^ ) 

src/NHibernate/Hql/Ast/ANTLR/HqlSqlWalker.g

@@ -432,8 +432,28 @@ arithmeticExpr
 	;
 
 caseExpr
-	: ^(CASE { _inCase = true; } (^(WHEN logicalExpr expr))+ (^(ELSE expr))?) { _inCase = false; }
-	| ^(CASE2 { _inCase = true; } expr (^(WHEN expr expr))+ (^(ELSE expr))?) { _inCase = false; }
+	: simpleCaseExpression
+	| searchedCaseExpression
+	;
+
+simpleCaseExpression
+	: ^(CASE2 {_inCase=true;} exprOrSubquery (simpleCaseWhenClause)+ (elseClause)?) {_inCase=false;}
+	;
+
+simpleCaseWhenClause
+	: ^(WHEN exprOrSubquery exprOrSubquery)
+	;
+
+elseClause
+	: ^(ELSE exprOrSubquery)
+	;
+
+searchedCaseExpression
+	: ^(CASE {_inCase = true;} (searchedCaseWhenClause)+ (elseClause)?) {_inCase = false;}
+	;
+
+searchedCaseWhenClause
+	: ^(WHEN logicalExpr exprOrSubquery)
 	;
 
 //TODO: I don't think we need this anymore .. how is it different to 

src/NHibernate/Linq/ReWriters/ConditionalQueryReferenceExpander.cs

@@ -31,6 +31,14 @@ public override void VisitSelectClause(SelectClause selectClause, QueryModel que
 			_expander.Transform(selectClause);
 		}
 
+		public override void VisitMainFromClause(MainFromClause fromClause, QueryModel queryModel)
+		{
+			if (fromClause.FromExpression is SubQueryExpression subqueryExpression)
+			{
+				VisitQueryModel(subqueryExpression.QueryModel);
+			}
+		}
+
 		public override void VisitOrdering(Ordering ordering, QueryModel queryModel, OrderByClause orderByClause, int index)
 		{
 			_expander.Transform(ordering);

src/NHibernate/Linq/ReWriters/SubQueryConditionalExpander.cs

@@ -24,6 +24,14 @@ public override void VisitSelectClause(SelectClause selectClause, QueryModel que
 			_expander.Transform(selectClause);
 		}
 
+		public override void VisitMainFromClause(MainFromClause fromClause, QueryModel queryModel)
+		{
+			if (fromClause.FromExpression is SubQueryExpression subqueryExpression)
+			{
+				VisitQueryModel(subqueryExpression.QueryModel);
+			}
+		}
+
 		public override void VisitOrdering(Ordering ordering, QueryModel queryModel, OrderByClause orderByClause, int index)
 		{
 			_expander.Transform(ordering);