fix query predicate bug for NotEqual expression type (#399)

Author: mdrakib

src/Redis.OM/Aggregation/AggregationPredicates/QueryPredicate.cs

@@ -148,7 +148,7 @@ protected override void SplitBinaryExpression(BinaryExpression expression, Stack
             }
         }
 
-        private static string BuildEqualityPredicate(MemberInfo member, ConstantExpression expression, string memberStr)
+        private static string BuildEqualityPredicate(MemberInfo member, ConstantExpression expression, string memberStr, bool negated = false)
         {
             var sb = new StringBuilder();
             var fieldAttribute = member.GetCustomAttribute<SearchFieldAttribute>();
@@ -157,6 +157,11 @@ private static string BuildEqualityPredicate(MemberInfo member, ConstantExpressi
                 throw new InvalidOperationException("Searches can only be performed on fields marked with a RedisFieldAttribute with the SearchFieldType not set to None");
             }
 
+            if (negated)
+            {
+                sb.Append("-");
+            }
+
             sb.Append($"{memberStr}:");
             var searchFieldType = fieldAttribute.SearchFieldType != SearchFieldType.INDEXED
                 ? fieldAttribute.SearchFieldType
@@ -189,7 +194,7 @@ private string BuildQueryPredicate(ExpressionType expType, MemberExpression memb
                 ExpressionType.GreaterThanOrEqual => $"{memberStr}:[{constExpression.Value} inf]",
                 ExpressionType.LessThanOrEqual => $"{memberStr}:[-inf {constExpression.Value}]",
                 ExpressionType.Equal => BuildEqualityPredicate(member.Member, constExpression, memberStr),
-                ExpressionType.NotEqual => $"{memberStr} : -{{{constExpression.Value}}}",
+                ExpressionType.NotEqual => BuildEqualityPredicate(member.Member, constExpression, memberStr, true),
                 _ => string.Empty
             };
             return queryPredicate;

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

@@ -271,5 +271,19 @@ public async Task GetGroupCount()
                 Assert.True(1<=result["COUNT"]);
             }
         }
+
+        [Fact]
+        public async Task GetGroupCountWithNegationQuery()
+        {
+            Setup();
+            var collection = new RedisAggregationSet<Person>(_connection);
+            var results = await collection
+                .Where(x => x.RecordShell.Age != 0)
+                .GroupBy(x => x.RecordShell.Age).CountGroupMembers().ToListAsync();
+            foreach (var result in results)
+            {
+                Assert.True(1 <= result["COUNT"]);
+            }
+        }
     }
 }