fix filter aggregation for string type on the right side (#328)

Author: imansafari1991

README.md

@@ -361,6 +361,7 @@ We'd love your contributions! If you want to contribute please read our [Contrib
 * [@mariusmuntean](https://github.com/mariusmuntean)
 * [@jcreus1](https://github.com/jcreus1)
 * [@JuliusMikkela](https://github.com/JuliusMikkela)
+* [@imansafari1991](https://github.com/imansafari1991)
 
 <!-- Logo -->
 [Logo]: images/logo.svg

src/Redis.OM/Common/ExpressionParserUtilities.cs

@@ -121,9 +121,9 @@ internal static string ParseBinaryExpression(BinaryExpression rootBinaryExpressi
             {
                 var right = GetOperandString(expression.Right);
                 var left = GetOperandString(expression.Left);
-
-                if (filterFormat && expression.Left is MemberExpression mem &&
-                    mem.Type == typeof(string))
+                if (filterFormat && ((expression.Left is MemberExpression mem &&
+                                      mem.Type == typeof(string)) || (expression.Left is UnaryExpression uni &&
+                                                                      uni.Type == typeof(string))))
                 {
                     right = $"'{right}'";
                 }

test/Redis.OM.Unit.Tests/RediSearchTests/AggregationSetTests.cs

@@ -387,6 +387,17 @@ public void TestMultipleOrderBys()
             _mock.Verify(x=>x.Execute("FT.AGGREGATE","person-idx", "*", "SORTBY", "4", "@Name", "ASC", "@Age", "DESC", "WITHCURSOR", "COUNT", "10000"));
         }
 
+        [Fact]
+        public void TestRightSideStringTypeFilter()
+        {
+            var collection = new RedisAggregationSet<Person>(_mock.Object, true, chunkSize: 10000);
+            _mock.Setup(x => x.Execute("FT.AGGREGATE", It.IsAny<string[]>())).Returns(MockedResult);
+            _mock.Setup(x => x.Execute("FT.CURSOR", It.IsAny<string[]>())).Returns(MockedResultCursorEnd);        
+            _ = collection.Apply(x => string.Format("{0} {1}", x.RecordShell.FirstName, x.RecordShell.LastName),
+                "FullName").Filter(p => p.Aggregations["FullName"] == "Bruce Wayne").ToList();
+            _mock.Verify(x => x.Execute("FT.AGGREGATE", "person-idx", "*", "APPLY", "format(\"%s %s\",@FirstName,@LastName)", "AS", "FullName", "FILTER", "@FullName == 'Bruce Wayne'", "WITHCURSOR", "COUNT", "10000"));
+        }
+        
         [Fact]
         public void TestNestedOrderBy()
         {

test/Redis.OM.Unit.Tests/RediSearchTests/Person.cs

@@ -66,5 +66,10 @@ public partial class Person
 
         [Indexed]
         public string? NullableStringField { get; set; }
+
+        [Indexed(Aggregatable = true)] public string FirstName { get; set; }
+        [Indexed(Aggregatable = true)] public string LastName { get; set; }
+
+
     }
 }