add nested filter on sort expresion

Author: unknown

src/Nest.Dsl.Factory/Factory/Sort/FieldSortBuilder.cs

@@ -8,6 +8,7 @@ public class FieldSortBuilder : ISortBuilder
         private object _missing;
         private SortOrder _order;
         private bool? _ignoreUnampped;
+        private TermFilterBuilder _nestedFilter;
 
         public FieldSortBuilder(string fieldName)
         {
@@ -26,6 +27,17 @@ public FieldSortBuilder IgnoreUnmapped(bool ignoreUnmapped)
             return this;
         }
 
+        /// <summary>
+        /// Sets sort nested filter
+        /// </summary>
+        /// <param name="nestedFilter">nested filter</param>
+        /// <returns></returns>
+        public FieldSortBuilder NestedFilter(TermFilterBuilder nestedFilter)
+        {
+            _nestedFilter = nestedFilter;
+            return this;
+        }
+
         #region ISortBuilder Members
 
         public ISortBuilder Order(SortOrder order)
@@ -60,6 +72,11 @@ public object ToJsonObject()
                 content[_fieldName]["ignore_unmapped"] = _ignoreUnampped;
             }
 
+            if (_nestedFilter != null)
+            {
+              content[_fieldName]["nested_filter"] = _nestedFilter.ToJsonObject() as JObject;
+            }
+
             return content;
         }