Added more sort-descriptors

Author: Grastveit

Diff for: src/Nest/DSL/SortDescriptor.cs

@@ -19,6 +19,9 @@ public class SortDescriptor<T> where T : class
 		[JsonProperty("order")]
 		internal string _Order { get; set; }
 
+        [JsonProperty("mode")]
+        internal string _Mode { get; set; }
+
 		[JsonProperty("nested_filter")]
 		internal BaseFilter _NestedFilter { get; set; }
 
@@ -70,6 +73,31 @@ public virtual SortDescriptor<T> Descending()
 			this._Order = "desc";
 			return this;
 		}
+
+        public virtual SortDescriptor<T> NestedMin()
+        {
+            this._Mode = "min";
+            return this;
+        }
+
+        public virtual SortDescriptor<T> NestedMax()
+        {
+            this._Mode = "max";
+            return this;
+        }
+
+        public virtual SortDescriptor<T> NestedSum()
+        {
+            this._Mode = "sum";
+            return this;
+        }
+
+        public virtual SortDescriptor<T> NestedAvg()
+        {
+            this._Mode = "avg";
+            return this;
+        }
+
 		public virtual SortDescriptor<T> NestedFilter(Func<FilterDescriptor<T>, BaseFilter> filterSelector)
 		{
 			filterSelector.ThrowIfNull("filterSelector");

Diff for: src/Tests/Nest.Tests.Unit/Search/Sort/SortTests.cs

@@ -61,6 +61,32 @@ public void TestSortOnSortField()
 			Assert.True(json.JsonEquals(expected), json);
 		}
 
+        [Test]
+        public void TestSortOnNestedField()
+        {
+            var s = new SearchDescriptor<ElasticsearchProject>()
+                .From(0)
+                .Size(10)
+                .Sort(sort => sort
+                    .OnField(e => e.Contributors.Suffix("age")) // Sort projects by oldest contributor
+                    .NestedMax()
+                    .Descending()
+                );
+            var json = TestElasticClient.Serialize(s);
+            var expected = @"
+                {
+                  from: 0,
+                  size: 10,
+                  sort: {
+                    ""contributors.age"": {
+                        ""order"": ""desc"",
+                        ""mode"": ""max""
+                    }
+                  }
+                }";
+            Assert.True(json.JsonEquals(expected), json);
+        }
+
 		[Test]
 		public void TestSortAscending()
 		{