NH-4030 - further simplifying Linq Future implementation.

Author: fredericDelaporte

src/NHibernate/Linq/DefaultQueryProvider.cs

@@ -13,7 +13,8 @@ namespace NHibernate.Linq
 {
 	public interface INhQueryProvider : IQueryProvider
 	{
-		object ExecuteFuture(Expression expression);
+		IEnumerable<TResult> ExecuteFuture<TResult>(Expression expression);
+		IFutureValue<TResult> ExecuteFutureValue<TResult>(Expression expression);
 		void SetResultTransformerAndAdditionalCriteria(IQuery query, NhLinqExpression nhExpression, IDictionary<string, Tuple<object, IType>> parameters);
 	}
 
@@ -59,12 +60,32 @@ public virtual IQueryable<T> CreateQuery<T>(Expression expression)
 			return new NhQueryable<T>(this, expression);
 		}
 
-		public virtual object ExecuteFuture(Expression expression)
+		public virtual IEnumerable<TResult> ExecuteFuture<TResult>(Expression expression)
 		{
-			IQuery query;
-			NhLinqExpression nhQuery;
-			NhLinqExpression nhLinqExpression = PrepareQuery(expression, out query, out nhQuery);
-			return ExecuteFutureQuery(nhLinqExpression, query, nhQuery);
+			PrepareQuery(expression, out var query, out var nhQuery);
+
+			var result = query.Future<TResult>();
+			SetupFutureResult(nhQuery, (IDelayedValue)result);
+
+			return result;
+		}
+
+		public virtual IFutureValue<TResult> ExecuteFutureValue<TResult>(Expression expression)
+		{
+			PrepareQuery(expression, out var query, out var nhQuery);
+
+			var result = query.FutureValue<TResult>();
+			SetupFutureResult(nhQuery, (IDelayedValue)result);
+
+			return result;
+		}
+
+		private static void SetupFutureResult(NhLinqExpression nhQuery, IDelayedValue result)
+		{
+			if (nhQuery.ExpressionToHqlTranslationResults.PostExecuteTransformer == null)
+				return;
+
+			result.ExecuteOnEval = nhQuery.ExpressionToHqlTranslationResults.PostExecuteTransformer;
 		}
 
 		protected virtual NhLinqExpression PrepareQuery(Expression expression, out IQuery query, out NhLinqExpression nhQuery)
@@ -80,24 +101,6 @@ protected virtual NhLinqExpression PrepareQuery(Expression expression, out IQuer
 			return nhLinqExpression;
 		}
 
-		private static readonly MethodInfo Future = ReflectHelper.GetMethodDefinition<IQuery>(q => q.Future<object>());
-		private static readonly MethodInfo FutureValue = ReflectHelper.GetMethodDefinition<IQuery>(q => q.FutureValue<object>());
-
-		protected virtual object ExecuteFutureQuery(NhLinqExpression nhLinqExpression, IQuery query, NhLinqExpression nhQuery)
-		{
-			var method = (nhLinqExpression.ReturnType == NhLinqExpressionReturnType.Sequence ? Future : FutureValue)
-				.MakeGenericMethod(nhQuery.Type);
-
-			object result = method.Invoke(query, new object[0]);
-
-			if (nhQuery.ExpressionToHqlTranslationResults.PostExecuteTransformer != null)
-			{
-				((IDelayedValue) result).ExecuteOnEval = nhQuery.ExpressionToHqlTranslationResults.PostExecuteTransformer;
-			}
-
-			return result;
-		}
-
 		protected virtual object ExecuteQuery(NhLinqExpression nhLinqExpression, IQuery query, NhLinqExpression nhQuery)
 		{
 			IList results = query.List();

src/NHibernate/Linq/LinqExtensionMethods.cs

@@ -99,8 +99,7 @@ public static IEnumerable<TSource> ToFuture<TSource>(this IQueryable<TSource> so
 			{
 				throw new NotSupportedException($"Source {nameof(source.Provider)} must be a {nameof(INhQueryProvider)}");
 			}
-			var future = provider.ExecuteFuture(source.Expression);
-			return (IEnumerable<TSource>)future;
+			return provider.ExecuteFuture<TSource>(source.Expression);
 		}
 
 		/// <summary>
@@ -122,13 +121,8 @@ public static IFutureValue<TSource> ToFutureValue<TSource>(this IQueryable<TSour
 			{
 				throw new NotSupportedException($"Source {nameof(source.Provider)} must be a {nameof(INhQueryProvider)}");
 			}
-			var future = provider.ExecuteFuture(source.Expression);
-			if (future is IEnumerable<TSource> enumerable)
-			{
-				return new FutureValue<TSource>(() => enumerable);
-			}
-
-			return (IFutureValue<TSource>)future;
+			var future = provider.ExecuteFuture<TSource>(source.Expression);
+			return new FutureValue<TSource>(() => future);
 		}
 
 		/// <summary>
@@ -156,7 +150,7 @@ public static IFutureValue<TResult> ToFutureValue<TSource, TResult>(this IQuerya
 			var expression = ReplacingExpressionTreeVisitor
 				.Replace(selector.Parameters.Single(), source.Expression, selector.Body);
 
-			return (IFutureValue<TResult>)provider.ExecuteFuture(expression);
+			return provider.ExecuteFutureValue<TResult>(expression);
 		}
 
 		public static T MappedAs<T>(this T parameter, IType type)