Fixing empty redis collection count bug (#74)

Author: slorello89

src/Redis.OM/Searching/RedisQueryProvider.cs

@@ -164,9 +164,20 @@ public async Task<IEnumerable<AggregationResult<T>>> ExecuteAggregationAsync<T>(
         public RedisReply ExecuteReductiveAggregation(MethodCallExpression expression, Type underpinningType)
         {
             var aggregation = ExpressionTranslator.BuildAggregationFromExpression(expression, underpinningType);
-            var res = AggregationResult.FromRedisResult(Connection.Execute("FT.AGGREGATE", aggregation.Serialize()));
+            var reply = Connection.Execute("FT.AGGREGATE", aggregation.Serialize());
+            var res = AggregationResult.FromRedisResult(reply);
             var reductionName = ((Reduction)aggregation.Predicates.Last()).ResultName;
-            return res.First()[reductionName];
+            if (res.Any())
+            {
+                return res.First()[reductionName];
+            }
+
+            if (reductionName == "COUNT")
+            {
+                return reply.ToArray().First();
+            }
+
+            throw new Exception("Invalid value returned by server");
         }
 
         /// <summary>

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

@@ -0,0 +1,10 @@
+using Redis.OM.Modeling;
+
+namespace Redis.OM.Unit.Tests.RediSearchTests
+{
+    [Document(IndexName = "empty-index")]
+    public class ClassForEmptyRedisCollection
+    {
+        [Indexed] public string TagField { get; set; }
+    }
+}

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

@@ -261,6 +261,15 @@ public void TestSetGetWithLoc()
             Assert.Equal(new GeoLoc(1.0,1.0), reconstituded.Home);
         }
 
+        [Fact]
+
+        public void TestCountWithEmptyCollection()
+        {
+            var collection = new RedisCollection<ClassForEmptyRedisCollection>(_connection);
+            var count = collection.Count();
+            Assert.Equal(0,count);
+        }
+      
         [Fact]
         public async Task TestUpdate()
         {

test/Redis.OM.Unit.Tests/RedisSetupCollection.cs

@@ -1,5 +1,6 @@
 using Redis.OM.Contracts;
 using System;
+using Redis.OM.Unit.Tests.RediSearchTests;
 using Xunit;
 
 namespace Redis.OM.Unit.Tests
@@ -15,7 +16,8 @@ public RedisSetup()
         {
             var personIndexExists = false;
             var hashPersonIndexExists = false;
-
+            var emptyIndexExists = false;
+            
             try
             {
                 Connection.Execute("FT.INFO", "person-idx");
@@ -36,10 +38,23 @@ public RedisSetup()
                 // ignored
             }
 
+            try
+            {
+                Connection.Execute("FT.INFO", "empty-index");
+                emptyIndexExists = true;
+            }
+            catch
+            {
+                //ignored
+            }
+
             if(!personIndexExists)
                 Connection.CreateIndex(typeof(RediSearchTests.Person));
             if (!hashPersonIndexExists)
                 Connection.CreateIndex(typeof(RediSearchTests.HashPerson));
+            if(!emptyIndexExists)
+                Connection.CreateIndex(typeof(ClassForEmptyRedisCollection));
+            
         }
 
         private IRedisConnection _connection = null;