Fix for VisitConditional: use string constant in true or false options.

Author: Oleg Nadymov

src/ServiceStack.OrmLite/Expressions/SqlExpression.cs

@@ -1814,16 +1814,27 @@ protected virtual object VisitConditional(ConditionalExpression e)
                 if ((bool) test)
                 {
                     var ifTrue = Visit(e.IfTrue);
+                    if (e.IfTrue.Type == typeof(string) && !(ifTrue is PartialSqlString))
+                        ifTrue = ConvertToParam(ifTrue);
+
                     return ifTrue;
                 }
 
                 var ifFalse = Visit(e.IfFalse);
+                if (e.IfFalse.Type == typeof(string) && !(ifFalse is PartialSqlString))
+                    ifFalse = ConvertToParam(ifFalse);
+
                 return ifFalse;
             }
             else
             {
                 var ifTrue = Visit(e.IfTrue);
+                if (e.IfTrue.Type == typeof(string) && !(ifTrue is PartialSqlString))
+                    ifTrue = ConvertToParam(ifTrue);
+
                 var ifFalse = Visit(e.IfFalse);
+                if (e.IfFalse.Type == typeof(string) && !(ifFalse is PartialSqlString))
+                    ifFalse = ConvertToParam(ifFalse);
 
                 return new PartialSqlString($"(CASE WHEN {test} THEN {ifTrue} ELSE {ifFalse} END)");
             }

tests/ServiceStack.OrmLite.Tests/ExpressionVisitorTests.cs

@@ -575,6 +575,17 @@ public void Can_Where_using_IfConcat_filter()
             Assert.That(target.Count, Is.EqualTo(1));
         }
 
+        [Test]
+        public void Can_Where_using_IfWithStringConstant_filter()
+        {
+            System.Linq.Expressions.Expression<Func<TestType, bool>> filter = x => (String.Concat("Text: ", x.TextCol) == null ? " " : String.Concat("Text: ", x.TextCol)).EndsWith("asdf");
+            var q = Db.From<TestType>().Where(filter);
+            Assert.That(q.ToSelectStatement(), Does.Contain("Text"));
+
+            var target = Db.Select(q);
+            Assert.That(target.Count, Is.EqualTo(1));
+        }
+
         private int MethodReturningInt(int val)
         {
             return val;