Support fetching individual lazy properties for Criteria EntityProjection

src/NHibernate.Test/Async/Criteria/EntityProjectionsTest.cs

@@ -47,7 +47,17 @@ protected override HbmMapping GetMappings()
 
 					rc.Property(x => x.Name);
 
-					rc.Property(ep => ep.LazyProp, m => m.Lazy(true));
+					rc.Property(ep => ep.LazyProp, m =>
+					{
+						m.Lazy(true);
+						m.FetchGroup("LazyProp1");
+					});
+
+					rc.Property(ep => ep.LazyProp2, m =>
+					{
+						m.Lazy(true);
+						m.FetchGroup("LazyProp2");
+					});
 
 					rc.ManyToOne(ep => ep.Child1, m => m.Column("Child1Id"));
 					rc.ManyToOne(ep => ep.Child2, m => m.Column("Child2Id"));
@@ -340,6 +350,26 @@ public async Task EntityProjectionWithLazyPropertiesFetchedAsync()
 				Assert.That(entityRoot, Is.Not.Null);
 				Assert.That(NHibernateUtil.IsInitialized(entityRoot), Is.True, "Object must be initialized");
 				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp)), Is.True, "Lazy property must be initialized");
+				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp2)), Is.True, "Lazy property must be initialized");
+			}
+		}
+
+		[Test]
+		public async Task EntityProjectionWithLazyPropertiesSinglePropertyFetchAsync()
+		{
+			using (var session = OpenSession())
+			{
+				EntityComplex entityRoot;
+				entityRoot = await (session
+							.QueryOver<EntityComplex>()
+							.Where(ec => ec.LazyProp != null)
+							.Select(Projections.RootEntity().SetFetchLazyPropertyGroups(nameof(entityRoot.LazyProp)))
+							.Take(1).SingleOrDefaultAsync());
+
+				Assert.That(entityRoot, Is.Not.Null);
+				Assert.That(NHibernateUtil.IsInitialized(entityRoot), Is.True, "Object must be initialized");
+				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp)), Is.True, "Lazy property must be initialized");
+				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp2)), Is.False, "Property must be lazy");
 			}
 		}
 

src/NHibernate.Test/Criteria/EntityProjectionsEntities.cs

@@ -24,6 +24,7 @@ public class EntityComplex
 		public virtual string Name { get; set; }
 
 		public virtual string LazyProp { get; set; }
+		public virtual string LazyProp2 { get; set; }
 
 		public virtual EntitySimpleChild Child1 { get; set; }
 		public virtual EntitySimpleChild Child2 { get; set; }

src/NHibernate.Test/Criteria/EntityProjectionsTest.cs

@@ -36,7 +36,17 @@ protected override HbmMapping GetMappings()
 
 					rc.Property(x => x.Name);
 
-					rc.Property(ep => ep.LazyProp, m => m.Lazy(true));
+					rc.Property(ep => ep.LazyProp, m =>
+					{
+						m.Lazy(true);
+						m.FetchGroup("LazyProp1");
+					});
+
+					rc.Property(ep => ep.LazyProp2, m =>
+					{
+						m.Lazy(true);
+						m.FetchGroup("LazyProp2");
+					});
 
 					rc.ManyToOne(ep => ep.Child1, m => m.Column("Child1Id"));
 					rc.ManyToOne(ep => ep.Child2, m => m.Column("Child2Id"));
@@ -329,6 +339,26 @@ public void EntityProjectionWithLazyPropertiesFetched()
 				Assert.That(entityRoot, Is.Not.Null);
 				Assert.That(NHibernateUtil.IsInitialized(entityRoot), Is.True, "Object must be initialized");
 				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp)), Is.True, "Lazy property must be initialized");
+				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp2)), Is.True, "Lazy property must be initialized");
+			}
+		}
+
+		[Test]
+		public void EntityProjectionWithLazyPropertiesSinglePropertyFetch()
+		{
+			using (var session = OpenSession())
+			{
+				EntityComplex entityRoot;
+				entityRoot = session
+							.QueryOver<EntityComplex>()
+							.Where(ec => ec.LazyProp != null)
+							.Select(Projections.RootEntity().SetFetchLazyPropertyGroups(nameof(entityRoot.LazyProp)))
+							.Take(1).SingleOrDefault();
+
+				Assert.That(entityRoot, Is.Not.Null);
+				Assert.That(NHibernateUtil.IsInitialized(entityRoot), Is.True, "Object must be initialized");
+				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp)), Is.True, "Lazy property must be initialized");
+				Assert.That(NHibernateUtil.IsPropertyInitialized(entityRoot, nameof(entityRoot.LazyProp2)), Is.False, "Property must be lazy");
 			}
 		}
 

src/NHibernate/Criterion/EntityProjection.cs

@@ -1,7 +1,9 @@
 using System;
+using System.Collections.Generic;
 using NHibernate.Engine;
 using NHibernate.Loader;
 using NHibernate.Loader.Criteria;
+using NHibernate.Persister.Entity;
 using NHibernate.SqlCommand;
 using NHibernate.Type;
 using IQueryable = NHibernate.Persister.Entity.IQueryable;
@@ -38,10 +40,16 @@ public EntityProjection(System.Type entityType, string entityAlias)
 		}
 
 		/// <summary>
-		/// Fetch lazy properties
+		/// Fetch all lazy properties
 		/// </summary>
 		public bool FetchLazyProperties { get; set; }
 
+		/// <summary>
+		/// Fetch individual lazy properties or property groups
+		/// Note: To fetch single property it must be mapped with unique fetch group (lazy-group)
+		/// </summary>
+		public ICollection<string> FetchLazyPropertyGroups { get; set; }
+
 		/// <summary>
 		/// Lazy load entity
 		/// </summary>
@@ -63,14 +71,25 @@ public EntityProjection SetLazy(bool lazy = true)
 		}
 
 		/// <summary>
-		/// Fetch lazy properties
+		/// Fetch all lazy properties
 		/// </summary>
 		public EntityProjection SetFetchLazyProperties(bool fetchLazyProperties = true)
 		{
 			FetchLazyProperties = fetchLazyProperties;
 			return this;
 		}
 
+		/// <summary>
+		/// Fetch individual lazy properties or property groups
+		/// Provide lazy property name and it will be fetched along with properties that belong to the same fetch group (lazy-group)
+		/// Note: To fetch single property it must be mapped with unique fetch group (lazy-group)
+		/// </summary>
+		public EntityProjection SetFetchLazyPropertyGroups(params string[] lazyPropertyGroups)
+		{
+			FetchLazyPropertyGroups = lazyPropertyGroups;
+			return this;
+		}
+
 		#endregion Configuration methods
 
 		#region IProjection implementation
@@ -115,7 +134,14 @@ SqlString IProjection.ToSqlString(ICriteria criteria, int position, ICriteriaQue
 					? identifierSelectFragment
 					: string.Concat(
 						identifierSelectFragment,
-						Persister.PropertySelectFragment(TableAlias, ColumnAliasSuffix, FetchLazyProperties)));
+						GetPropertySelectFragment()));
+		}
+
+		private string GetPropertySelectFragment()
+		{
+			return FetchLazyProperties
+				? Persister.PropertySelectFragment(TableAlias, ColumnAliasSuffix, FetchLazyProperties)
+				: Persister.PropertySelectFragment(TableAlias, ColumnAliasSuffix, FetchLazyPropertyGroups);
 		}
 
 		SqlString IProjection.ToGroupSqlString(ICriteria criteria, ICriteriaQuery criteriaQuery)

src/NHibernate/Loader/AbstractEntityJoinWalker.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using NHibernate.Criterion;
 using NHibernate.Engine;
-using NHibernate.Loader.Criteria;
 using NHibernate.Persister.Entity;
 using NHibernate.SqlCommand;
 using NHibernate.Type;
@@ -62,6 +61,7 @@ protected void InitProjection(SqlString projectionString, SqlString whereString,
 				var associations = new OuterJoinableAssociation[countEntities];
 				var eagerProps = new bool[countEntities];
 				var suffixes = new string[countEntities];
+				var fetchLazyProperties = new ISet<string>[countEntities];
 				for (var i = 0; i < countEntities; i++)
 				{
 					var e = entityProjections[i];
@@ -70,13 +70,19 @@ protected void InitProjection(SqlString projectionString, SqlString whereString,
 					{
 						eagerProps[i] = true;
 					}
+
+					if (e.FetchLazyPropertyGroups?.Count > 0)
+					{
+						fetchLazyProperties[i] = new HashSet<string>(e.FetchLazyPropertyGroups);
+					}
 					suffixes[i] = e.ColumnAliasSuffix;
 				}
 
 				InitPersisters(associations, lockMode);
 
 				Suffixes = suffixes;
 				EagerPropertyFetches = eagerProps;
+				EntityFetchLazyProperties = fetchLazyProperties;
 			}
 			else
 			{

src/NHibernate/Loader/OuterJoinableAssociation.cs

@@ -236,7 +236,8 @@ internal string GetSelectFragment(string entitySuffix, string collectionSuffix,
 						                    ShouldFetchCollectionPersister(),
 						                    new EntityLoadInfo(entitySuffix)
 						                    {
-							                    LazyProperties = EntityFetchLazyProperties
+							                    LazyProperties = EntityFetchLazyProperties,
+							                    IncludeLazyProps = SelectMode == SelectMode.FetchLazyProperties,
 						                    });
 				case SelectMode.ChildFetch:
 					return ReflectHelper.CastOrThrow<ISupportSelectModeJoinable>(Joinable, "child fetch select mode")

src/NHibernate/Persister/Entity/IQueryable.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using NHibernate.Util;
 
 namespace NHibernate.Persister.Entity
@@ -16,7 +17,7 @@ internal static class AbstractEntityPersisterExtensions
 		/// Given a query alias and an identifying suffix, render the property select fragment.
 		/// </summary>
 		//6.0 TODO: Merge into IQueryable
-		public static string PropertySelectFragment(this IQueryable query, string alias, string suffix, string[] fetchProperties)
+		public static string PropertySelectFragment(this IQueryable query, string alias, string suffix, ICollection<string> fetchProperties)
 		{
 			return ReflectHelper.CastOrThrow<AbstractEntityPersister>(query, "individual lazy property fetches")
 			                    .PropertySelectFragment(alias, suffix, fetchProperties);

src/NHibernate/SelectMode.cs

@@ -33,12 +33,13 @@ public enum SelectMode
 		JoinOnly,
 
 		/// <summary>
-		/// Skips fetching for eagerly mapped association (no-op for lazy association).
+		/// Skips fetching for fetch="join" association (no-op for lazy association).
 		/// </summary>
 		Skip,
 
 		/// <summary>
-		/// Fetch lazy property group
+		/// Fetch lazy property group.
+		/// Provide path to lazy property and it will be fetched along with properties that belong to the same fetch group (lazy-group)
 		/// Note: To fetch single property it must be mapped with unique fetch group (lazy-group)
 		/// </summary>
 		FetchLazyPropertyGroup,