Call generic query.List from Linq queries (#2238)

Author: bahusoid

src/NHibernate.Test/Linq/ByMethod/WithOptionsTests.cs

@@ -23,6 +23,7 @@ public void AppliesOptionsToQuery()
 			var query = Substitute.For<IQuery>();
 
 			query.List().Returns(new List<Order>());
+			query.List<Order>().Returns(new List<Order>());
 
 			session.CreateQuery(Arg.Any<IQueryExpression>()).Returns(query);
 
@@ -56,6 +57,7 @@ public void DoNotContaminateQueryWithOptions()
 			var query = Substitute.For<IQuery>();
 
 			query.List().Returns(new List<Order>());
+			query.List<Order>().Returns(new List<Order>());
 
 			session.CreateQuery(Arg.Any<IQueryExpression>()).Returns(query);
 

src/NHibernate/Async/Linq/DefaultQueryProvider.cs

@@ -32,6 +32,23 @@ public partial interface INhQueryProvider : IQueryProvider
 	public partial class DefaultQueryProvider : INhQueryProvider, IQueryProviderWithOptions, ISupportFutureBatchNhQueryProvider
 	{
 
+		//TODO 6.0: Add to INhQueryProvider interface 
+		public virtual async Task<IList<TResult>> ExecuteListAsync<TResult>(Expression expression, CancellationToken cancellationToken)
+		{
+			cancellationToken.ThrowIfCancellationRequested();
+			var linqExpression = PrepareQuery(expression, out var query);
+			var resultTransformer = linqExpression.ExpressionToHqlTranslationResults?.PostExecuteTransformer;
+			if (resultTransformer == null)
+			{
+				return await (query.ListAsync<TResult>(cancellationToken)).ConfigureAwait(false);
+			}
+
+			return new List<TResult>
+			{
+				(TResult) resultTransformer.DynamicInvoke((await (query.ListAsync(cancellationToken)).ConfigureAwait(false)).AsQueryable())
+			};
+		}
+
 		// Since v5.1
 		[Obsolete("Use ExecuteQuery(NhLinqExpression nhLinqExpression, IQuery query) instead")]
 		protected virtual async Task<object> ExecuteQueryAsync(NhLinqExpression nhLinqExpression, IQuery query, NhLinqExpression nhQuery, CancellationToken cancellationToken)

src/NHibernate/Linq/DefaultQueryProvider.cs

@@ -100,6 +100,22 @@ public TResult Execute<TResult>(Expression expression)
 			return (TResult)Execute(expression);
 		}
 
+		//TODO 6.0: Add to INhQueryProvider interface 
+		public virtual IList<TResult> ExecuteList<TResult>(Expression expression)
+		{
+			var linqExpression = PrepareQuery(expression, out var query);
+			var resultTransformer = linqExpression.ExpressionToHqlTranslationResults?.PostExecuteTransformer;
+			if (resultTransformer == null)
+			{
+				return query.List<TResult>();
+			}
+
+			return new List<TResult>
+			{
+				(TResult) resultTransformer.DynamicInvoke(query.List().AsQueryable())
+			};
+		}
+
 		public IQueryProvider WithOptions(Action<NhQueryableOptions> setOptions)
 		{
 			if (setOptions == null) throw new ArgumentNullException(nameof(setOptions));

src/NHibernate/Linq/LinqExtensionMethods.cs

@@ -2389,8 +2389,11 @@ public static class LinqExtensionMethods
 
 			async Task<List<TSource>> InternalToListAsync()
 			{
-				var result = await provider.ExecuteAsync<IEnumerable<TSource>>(source.Expression, cancellationToken).ConfigureAwait(false);
-				return result.ToList();
+				//TODO 6.0: Replace with provider.ExecuteListAsync
+				var result = provider is DefaultQueryProvider nhQueryProvider
+					? await nhQueryProvider.ExecuteListAsync<TSource>(source.Expression, cancellationToken).ConfigureAwait(false)
+					: await provider.ExecuteAsync<IEnumerable<TSource>>(source.Expression, cancellationToken).ConfigureAwait(false);
+				return (result as List<TSource>) ?? result.ToList();
 			}
 		}
 

src/NHibernate/Linq/NhQueryable.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Linq.Expressions;
 using NHibernate.Engine;
@@ -17,7 +18,7 @@ interface IEntityNameProvider
 	/// <summary>
 	/// Provides the main entry point to a LINQ query.
 	/// </summary>
-	public class NhQueryable<T> : QueryableBase<T>, IEntityNameProvider
+	public class NhQueryable<T> : QueryableBase<T>, IEntityNameProvider, IEnumerable<T>
 	{
 		// This constructor is called by our users, create a new IQueryExecutor.
 		public NhQueryable(ISessionImplementor session)
@@ -57,5 +58,14 @@ public override string ToString()
 		{
 			return "NHibernate.Linq.NhQueryable`1[" + EntityName + "]";
 		}
+
+		IEnumerator<T> IEnumerable<T>.GetEnumerator()
+		{
+			//TODO 6.0: Cast to INhQueryProvider
+			return
+				Provider is DefaultQueryProvider nhProvider
+					? nhProvider.ExecuteList<T>(Expression).GetEnumerator()
+					: base.GetEnumerator();
+		}
 	}
 }