added condition to lazy loading of relationship objects

no db calls will be made if foreign key is 0.

Marr.Data/LazyLoaded.cs

@@ -70,14 +70,15 @@ namespace Marr.Data
     internal class LazyLoaded<TParent, TChild> : LazyLoaded<TChild>
     {
         private TParent _parent;
-        private Func<IDataMapper, TParent, TChild> _query;
-        
         private Func<IDataMapper> _dbCreator;
 
-        internal LazyLoaded(Func<IDataMapper, TParent, TChild> query) 
+        private readonly Func<IDataMapper, TParent, TChild> _query;
-            : base()
+        private readonly Func<TParent, bool> _condition;
+
+        internal LazyLoaded(Func<IDataMapper, TParent, TChild> query, Func<TParent, bool> condition = null)
         {
             _query = query;
+            _condition = condition;
         }
 
         public LazyLoaded(TChild val) 
@@ -106,13 +107,18 @@ namespace Marr.Data
         public override void LazyLoad()
         {
             if (!_isLoaded)
+            {
+                if (_condition != null && _condition(_parent))
                 {
                     using (IDataMapper db = _dbCreator())
                     {
                         _child = _query(db, _parent);
-                    _isLoaded = true;
                     }
                 }
+
+                _child = default(TChild);
+                _isLoaded = true;
+            }
         }
 
         public static implicit operator LazyLoaded<TParent, TChild>(TChild val)

Marr.Data/Mapping/RelationshipBuilder.cs

@@ -62,12 +62,13 @@ namespace Marr.Data.Mapping
         /// </summary>
         /// <typeparam name="TChild"></typeparam>
         /// <param name="query"></param>
+        /// <param name="condition">condition in which a child could exist. eg. avoid call to db if foreign key is 0 or null</param>
         /// <returns></returns>
-        public RelationshipBuilder<TEntity> LazyLoad<TChild>(Func<IDataMapper, TEntity, TChild> query)
+        public RelationshipBuilder<TEntity> LazyLoad<TChild>(Func<IDataMapper, TEntity, TChild> query, Func<TEntity, bool> condition = null)
         {
             AssertCurrentPropertyIsSet();
 
-            Relationships[_currentPropertyName].LazyLoaded = new LazyLoaded<TEntity, TChild>(query);
+            Relationships[_currentPropertyName].LazyLoaded = new LazyLoaded<TEntity, TChild>(query, condition);
             return this;
         }
 

NzbDrone.Core.Test/Datastore/DatabaseRelationshipFixture.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using FizzWare.NBuilder;
 using FluentAssertions;
 using NUnit.Framework;
+using NzbDrone.Core.MediaFiles;
 using NzbDrone.Core.Qualities;
 using NzbDrone.Core.Test.Framework;
 using NzbDrone.Core.Tv;
@@ -72,29 +73,41 @@ namespace NzbDrone.Core.Test.Datastore
                     loadedSeries.Covers.Value.Should().HaveSameCount(covers);
                 }*/
 
-//        [Test]
+        [Test]
-//        public void one_to_one()
+        public void one_to_one()
-//        {
+        {
-//            var episode = Builder<Episode>.CreateNew()
+            var episodeFile = Builder<EpisodeFile>.CreateNew()
-//                                                       .With(c => c.Id = 0)
+                           .BuildNew();
-//                                                       .Build();
+
-//
+            Db.Insert(episodeFile);
-//            Db.Insert(episode);
+
-//
+            var episode = Builder<Episode>.CreateNew()
-//
+                .With(c => c.EpisodeFileId = episodeFile.Id)
-//            var history = Builder<History.History>.CreateNew()
+                .BuildNew();
-//                            .With(c => c.Id = 0)
+
-//                            .With(c => c.EpisodeId = episode.Id)
+            Db.Insert(episode);
-//                            .With(c => c.Quality = new QualityModel())
+
-//                            .Build();
+
-//
+
-//            Db.Insert(history);
+
-//
+
-//            var loadedEpisode = Db.Single<History.History>().Episode.Value;
+            var loadedEpisodeFile = Db.Single<Episode>().EpisodeFile.Value;
-//
+
-//            loadedEpisode.Should().NotBeNull();
+            loadedEpisodeFile.Should().NotBeNull();
-//            loadedEpisode.ShouldHave().AllProperties().But(c => c.SeriesTitle).EqualTo(episode);
+            loadedEpisodeFile.ShouldHave().AllProperties().But(c => c.DateAdded).EqualTo(episodeFile);
-//        }
+        }
+
+        [Test]
+        public void one_to_one_should_not_query_db_if_foreign_key_is_zero()
+        {
+            var episode = Builder<Episode>.CreateNew()
+                .With(c => c.EpisodeFileId = 0)
+                .BuildNew();
+
+            Db.Insert(episode);
+
+            Db.Single<Episode>().EpisodeFile.Value.Should().BeNull();
+        }
 
 
         [Test]

NzbDrone.Core/Datastore/RelationshipExtensions.cs

@@ -13,8 +13,10 @@ namespace NzbDrone.Core.Datastore
             where TChild : ModelBase
         {
             return relationshipBuilder.For(portalExpression.GetMemberName())
-                                .LazyLoad((db, parent) => db.Query<TChild>()
+                                .LazyLoad(
-                                .SingleOrDefault(c => c.Id == childIdSelector(parent)));
+                                            query: (db, parent) => db.Query<TChild>().SingleOrDefault(c => c.Id == childIdSelector(parent)),
+                                            condition: parent => childIdSelector(parent) > 0
+                                         );
 
         }