Unified check whether LeftJoin should be used

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Linq/Expressions/ItemProjectorExpression.cs

@@ -145,10 +145,9 @@ public ItemProjectorExpression EnsureEntityIsJoined()
             rightIndex++;
           }
           var offset = dataSource.Header.Length;
-          dataSource = entityExpression.IsNullable
-            || (dataSource is JoinProvider dataSourceAsJoin && dataSourceAsJoin.JoinType == JoinType.LeftOuter)
-              ? dataSource.LeftJoin(joinedRs, keyPairs)
-              : dataSource.Join(joinedRs, keyPairs);
+          dataSource = entityExpression.IsNullable || dataSource.CheckIfUseLeftJoin()
+            ? dataSource.LeftJoin(joinedRs, keyPairs)
+            : dataSource.Join(joinedRs, keyPairs);
           EntityExpression.Fill(entityExpression, offset);
           return entityExpression;
         }
@@ -169,10 +168,9 @@ public ItemProjectorExpression EnsureEntityIsJoined()
             rightIndex++;
           }
           var offset = dataSource.Header.Length;
-          dataSource = entityFieldExpression.IsNullable
-            || (dataSource is JoinProvider dataSourceAsJoin && dataSourceAsJoin.JoinType == JoinType.LeftOuter)
-              ? dataSource.LeftJoin(joinedRs, keyPairs)
-              : dataSource.Join(joinedRs, keyPairs);
+          dataSource = entityFieldExpression.IsNullable || dataSource.CheckIfUseLeftJoin()
+            ? dataSource.LeftJoin(joinedRs, keyPairs)
+            : dataSource.Join(joinedRs, keyPairs);
           entityFieldExpression.RegisterEntityExpression(offset);
           return entityFieldExpression.Entity;
         }

Orm/Xtensive.Orm/Orm/Linq/Translator.Expressions.cs

@@ -1650,7 +1650,8 @@ public void EnsureEntityFieldsAreJoined(EntityExpression entityExpression, ItemP
         .ToArray();
       int offset = itemProjector.DataSource.Header.Length;
       var oldDataSource = itemProjector.DataSource;
-      var newDataSource = entityExpression.IsNullable
+
+      var newDataSource = entityExpression.IsNullable || oldDataSource.CheckIfUseLeftJoin()
         ? itemProjector.DataSource.LeftJoin(joinedRs, keyPairs)
         : itemProjector.DataSource.Join(joinedRs, keyPairs);
       itemProjector.DataSource = newDataSource;
@@ -1675,15 +1676,15 @@ private void EnsureEntityReferenceIsJoined(EntityFieldExpression entityFieldExpr
 
       var oldDataSource = originalItemProjector.DataSource;
       var offset = oldDataSource.Header.Length;
-      var shouldUseLeftJoin = false;
+      //var shouldUseLeftJoin = false;
 
-      var sourceToCheck = (oldDataSource is FilterProvider filterProvider) ? filterProvider.Source : oldDataSource;
-      if ((sourceToCheck is ApplyProvider applyProvider && applyProvider.ApplyType == JoinType.LeftOuter) ||
-          (sourceToCheck is JoinProvider joinProvider && joinProvider.JoinType == JoinType.LeftOuter)) {
-        shouldUseLeftJoin = true;
-      }
+      //var sourceToCheck = (oldDataSource is FilterProvider filterProvider) ? filterProvider.Source : oldDataSource;
+      //if ((sourceToCheck is ApplyProvider applyProvider && applyProvider.ApplyType == JoinType.LeftOuter) ||
+      //    (sourceToCheck is JoinProvider joinProvider && joinProvider.JoinType == JoinType.LeftOuter)) {
+      //  shouldUseLeftJoin = true;
+      //}
 
-      var newDataSource = entityFieldExpression.IsNullable || shouldUseLeftJoin
+      var newDataSource = entityFieldExpression.IsNullable || oldDataSource.CheckIfUseLeftJoin()
         ? oldDataSource.LeftJoin(joinedRs, keyPairs)
         : oldDataSource.Join(joinedRs, keyPairs);
       originalItemProjector.DataSource = newDataSource;

Orm/Xtensive.Orm/Orm/Rse/CompilableProviderExtensions.cs

@@ -212,5 +212,12 @@ public static CompilableProvider MakeVoid(this CompilableProvider source)
     {
       return new VoidProvider(source.Header);
     }
+
+    internal static bool CheckIfUseLeftJoin(this CompilableProvider provider)
+    {
+      var sourceToCheck = (provider is FilterProvider filterProvider) ? filterProvider.Source : provider;
+      return (sourceToCheck is ApplyProvider applyProvider && applyProvider.ApplyType == JoinType.LeftOuter) ||
+        (sourceToCheck is JoinProvider joinProvider && joinProvider.JoinType == JoinType.LeftOuter);
+    }
   }
 }