Add weight function to function score query

Closes #1223

Author: gmarz

src/Nest/DSL/Query/Functions/FunctionScoreFunctionsDescriptor.cs

@@ -78,6 +78,14 @@ public FunctionScoreFunction<T> FieldValueFactor(Action<FieldValueFactorDescript
 			this._Functions.Add(fn);
 			return fn;
 		}
+
+		public FunctionScoreFunction<T> Weight(double weight)
+		{
+			var fn = new WeightFunction<T>(weight);
+			this._Functions.Add(fn);
+			return fn;
+		}
+
 		public IEnumerator<FunctionScoreFunction<T>> GetEnumerator()
 		{
 			return _Functions.GetEnumerator();

src/Nest/DSL/Query/Functions/WeightFunction.cs

@@ -0,0 +1,20 @@
+using Newtonsoft.Json;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Nest
+{
+	[JsonObject(MemberSerialization = MemberSerialization.OptIn)]
+	public class WeightFunction<T> : FunctionScoreFunction<T> where T : class
+	{
+		[JsonProperty(PropertyName = "weight")]
+		internal double _Weight { get; set; }
+
+		public WeightFunction(double weight)
+		{
+			_Weight = weight;
+		}
+	}
+}

src/Nest/Nest.csproj

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
-   <PropertyGroup>
+  <PropertyGroup>
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
     <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
     <ProjectGuid>{072BA7DA-7B60-407D-8B6E-95E3186BE70C}</ProjectGuid>
@@ -234,6 +234,7 @@
     <Compile Include="DSL\Aggregations\ReverseNestedAggregationDescriptor.cs" />
     <Compile Include="DSL\Filter\IndicesFilterDescriptor.cs" />
     <Compile Include="Domain\DSL\NoMatchShortcut.cs" />
+    <Compile Include="DSL\Query\Functions\WeightFunction.cs" />
     <Compile Include="DSL\UpgradeDescriptor.cs" />
     <Compile Include="DSL\UpgradeStatusDescriptor.cs" />
     <Compile Include="DSL\VerifyRepositoryDescriptor.cs" />
@@ -1140,4 +1141,4 @@
       </ItemGroup>
     </When>
   </Choose>
-</Project>
+</Project>

src/Tests/Nest.Tests.Unit/QueryParsers/Queries/FunctionScoreQueryTests.cs

@@ -20,7 +20,8 @@ public void FunctionScore_Deserializes()
 						ff => ff.Gauss(x => x.StartedOn, d => d.Scale("42w")).Weight(1),
 						ff => ff.Linear(x => x.FloatValue, d => d.Scale("0.3")).Filter(lff=>Filter2).Weight(2),
 						ff => ff.Exp(x => x.DoubleValue, d => d.Scale("0.5")).Weight(3),
-						ff => ff.BoostFactor(2).Filter(bff=>Filter1)
+						ff => ff.BoostFactor(2).Filter(bff=>Filter1),
+						ff => ff.Weight(5.0).Filter(wf =>Filter1)
 					)
 					.Query(qq=>Query1)
 					.RandomScore(1337)
@@ -45,11 +46,11 @@ public void FunctionScore_Deserializes()
 			param.Should().NotBeNull();
 			param.Key.Should().Be("param");
 			param.Value.Should().Be("paramvalue");
-			q.Functions.Should().NotBeEmpty().And.HaveCount(4);
+			q.Functions.Should().NotBeEmpty().And.HaveCount(5);
 
 			//TODO rip out state from all these function descriptors
 			var functions = q.Functions.ToList();
-			functions.Should().NotBeEmpty().And.HaveCount(4);
+			functions.Should().NotBeEmpty().And.HaveCount(5);
 
 
 		}

src/Tests/Nest.Tests.Unit/Search/Query/Singles/FunctionScoreQueryJson.cs

@@ -14,6 +14,7 @@ public void FunctionScoreQuery()
 					.FunctionScore(fs => fs
 						.Query(qq => qq.MatchAll())
 						.Functions(
+						    f => f.Weight(3.0).Filter(ff => ff.Term(p => p.Name, "elasticsearch")),
 							f => f.Gauss(x => x.StartedOn, d => d.Scale("42w")),
 							f => f.Linear(x => x.FloatValue, d => d.Scale("0.3")),
 							f => f.Exp(x => x.DoubleValue, d => d.Scale("0.5")),
@@ -32,6 +33,7 @@ public void FunctionScoreQuery()
 				query : {
                     function_score : { 
                         functions: [
+							{weight: 3.0, filter: { term: { 'name': 'elasticsearch' }}},
                             {gauss:  { startedOn  : { scale: '42w'}}},
                             {linear: { floatValue : { scale: '0.3'}}},
                             {exp:    { doubleValue: { scale: '0.5'}}},