Treat "null != column" the same way as "column != null" in SqlExpression

Author: shift-evgeny

src/ServiceStack.OrmLite/Expressions/SqlExpression.cs

@@ -1295,6 +1295,14 @@ protected virtual object VisitBinary(BinaryExpression b)
                 }
             }
 
+            if (left.ToString().Equals("null", StringComparison.OrdinalIgnoreCase))
+            {
+                // "null is x" will not work, so swap the operands
+                var temp = right;
+                right = left;
+                left = temp;
+            }
+
             if (operand == "=" && right.ToString().Equals("null", StringComparison.OrdinalIgnoreCase))
                 operand = "is";
             else if (operand == "<>" && right.ToString().Equals("null", StringComparison.OrdinalIgnoreCase))

tests/ServiceStack.OrmLite.Tests/ExpressionVisitorTests.cs

@@ -185,6 +185,14 @@ public void Can_Select_using_Nullable_HasValue()
             CollectionAssert.AreEquivalent(new[] { 2 }, target.Select(t => t.Id).ToArray());
         }
 
+        [Test]
+        public void Can_Select_using_constant_Yoda_condition()
+        {
+            var q = Db.From<TestType>().Where(x => null != x.NullableIntCol); // "null != x.NullableIntCol" should be the same as "x.NullableIntCol != null"
+            var target = Db.Select(q);
+            CollectionAssert.AreEquivalent(new[] { 1, 3, 4 }, target.Select(t => t.Id).ToArray());
+        }
+
         [Test]
         public void Can_Select_using_Startswith()
         {