diff --git a/Test.GBase/GBaseIntegrationTest/GBaseIntegrationTest.cs b/Test.GBase/GBaseIntegrationTest/GBaseIntegrationTest.cs
index 50a8541..e503539 100644
--- a/Test.GBase/GBaseIntegrationTest/GBaseIntegrationTest.cs
+++ b/Test.GBase/GBaseIntegrationTest/GBaseIntegrationTest.cs
@@ -48,9 +48,9 @@ namespace Test.GBase.GBaseIntegrationTest
             await model.AddItem(new Item("Item 2", 2), _cancellationTokenSource.Token);
             await model.AddItem(new Item("Item 3", 3), _cancellationTokenSource.Token);
 
-            await model.AddGroup(new Group(1), _cancellationTokenSource.Token);
-            await model.AddGroup(new Group(2), _cancellationTokenSource.Token);
-            await model.AddGroup(new Group(3), _cancellationTokenSource.Token);
+            await model.AddGroup(new Group(1) {Items = { model.Items[0], model.Items[1] }}, _cancellationTokenSource.Token);
+            await model.AddGroup(new Group(2) {Items = { model.Items[1], model.Items[2] }}, _cancellationTokenSource.Token);
+            await model.AddGroup(new Group(3) {Items = { model.Items[0], model.Items[2] }}, _cancellationTokenSource.Token);
         }
     }
 }
\ No newline at end of file
diff --git a/Test.GBase/GBaseIntegrationTest/Group.cs b/Test.GBase/GBaseIntegrationTest/Group.cs
index 970712f..7917268 100644
--- a/Test.GBase/GBaseIntegrationTest/Group.cs
+++ b/Test.GBase/GBaseIntegrationTest/Group.cs
@@ -13,18 +13,21 @@ namespace Test.GBase.GBaseIntegrationTest
     {
         public Group()
         {
-            Items = new List<IItem>();
+            Items = new List<Item>();
         }
         
         public Group(int number)
         {
             Number = number;
-            Items = new List<IItem>();
+            Items = new List<Item>();
         }
 
         [GBaseColumn]
         public int Number { get; private set; }
-        public List<IItem> Items { get; }
+        
+        [GBaseColumn]
+        public List<Item> Items { get; }
+        
         public GBaseKey Key { get; set; }
         public string FileName => $"Group{Number}";
 
diff --git a/Test.GBase/GBaseIntegrationTest/IGroup.cs b/Test.GBase/GBaseIntegrationTest/IGroup.cs
index 848f881..9fc4e1b 100644
--- a/Test.GBase/GBaseIntegrationTest/IGroup.cs
+++ b/Test.GBase/GBaseIntegrationTest/IGroup.cs
@@ -11,6 +11,6 @@ namespace Test.GBase.GBaseIntegrationTest
     public interface IGroup : IGBaseObject //: INotifyGBaseEntryChanged
     {
         int Number { get; }
-        List<IItem> Items { get; }
+        List<Item> Items { get; }
     }
 }
\ No newline at end of file
diff --git a/Test.GBase/GBaseIntegrationTest/Model.cs b/Test.GBase/GBaseIntegrationTest/Model.cs
index a446b8f..8ca67de 100644
--- a/Test.GBase/GBaseIntegrationTest/Model.cs
+++ b/Test.GBase/GBaseIntegrationTest/Model.cs
@@ -19,23 +19,23 @@ namespace Test.GBase.GBaseIntegrationTest
         public Model(IGBaseFactory gBaseFactory)
         {
             _gBase = gBaseFactory.Create(new Settings());
-            Items = new List<IItem>();
-            Groups = new List<IGroup>();
+            Items = new List<Item>();
+            Groups = new List<Group>();
         }
         
-        public List<IItem> Items { get; private set; }
-        public List<IGroup> Groups { get; private set; }
+        public List<Item> Items { get; private set; }
+        public List<Group> Groups { get; private set; }
 
         public async Task Initialize(CancellationToken cancellationToken)
         {
             await _gBase.Init("DB", Assembly.GetExecutingAssembly(), cancellationToken);
 
             IGBaseTable<Item> itemsTable = _gBase.GetTable<Item>();
-            Items = itemsTable.Entries.Cast<IItem>().ToList();
+            Items = itemsTable.Entries.ToList();
             //Items = (await _gBase.GetValues<Model, Item>(this, nameof(Items), cancellationToken)).Cast<IItem>().ToList();
             
             IGBaseTable<Group> groupsTable = _gBase.GetTable<Group>();
-            Groups = groupsTable.Entries.Cast<IGroup>().ToList();
+            Groups = groupsTable.Entries.ToList();
             //Groups = (await _gBase.GetValues<Model, Group>(this, nameof(Groups), cancellationToken)).Cast<IGroup>().ToList();
         }