Add rank_feature, rank_feature fields and rank_feature query (#3941)

This commit adds the rank_feature, rank_feature fields and rank_feature query

* Add rank_feature property
* Add rank_features property
* Add rank_feature query
* fix FieldCapabilities integration test

Closes #3938

(cherry picked from commit 453a608)

Author: russcam

docs/code-standards/descriptors.asciidoc

@@ -204,6 +204,9 @@ var methods = from d in YieldAllDescriptors()
     where !(m.Name == nameof(RuleConditionDescriptor.AppliesTo) && dt == typeof(RuleConditionDescriptor))
     where !(m.Name == nameof(RuleConditionDescriptor.Operator) && dt == typeof(RuleConditionDescriptor))
     where !(m.Name == nameof(RuleConditionDescriptor.Value) && dt == typeof(RuleConditionDescriptor))
+    where !(m.Name == nameof(RankFeatureLogarithmFunctionDescriptor.ScalingFactor) && dt == typeof(RankFeatureLogarithmFunctionDescriptor))
+    where !(m.Name == nameof(RankFeatureSigmoidFunctionDescriptor.Exponent) && dt == typeof(RankFeatureSigmoidFunctionDescriptor))
+    where !(m.Name == nameof(RankFeatureSigmoidFunctionDescriptor.Pivot) && dt == typeof(RankFeatureSigmoidFunctionDescriptor))
 
     select new {m, d, p};
 

docs/query-dsl.asciidoc

@@ -273,6 +273,8 @@ Specialized types of queries that do not fit into other groups
 
 * <<percolate-query-usage,Percolate Query Usage>>
 
+* <<rank-feature-query-usage,Rank Feature Query Usage>>
+
 * <<script-query-usage,Script Query Usage>>
 
 * <<script-score-query-usage,Script Score Query Usage>>
@@ -287,6 +289,8 @@ include::query-dsl/specialized/more-like-this/more-like-this-query-usage.asciido
 
 include::query-dsl/specialized/percolate/percolate-query-usage.asciidoc[]
 
+include::query-dsl/specialized/rank-feature/rank-feature-query-usage.asciidoc[]
+
 include::query-dsl/specialized/script/script-query-usage.asciidoc[]
 
 include::query-dsl/specialized/script-score/script-score-query-usage.asciidoc[]

docs/query-dsl/specialized/rank-feature/rank-feature-query-usage.asciidoc

@@ -0,0 +1,65 @@
+:ref_current: https://www.elastic.co/guide/en/elasticsearch/reference/7.0
+
+:github: https://github.com/elastic/elasticsearch-net
+
+:nuget: https://www.nuget.org/packages
+
+////
+IMPORTANT NOTE
+==============
+This file has been generated from https://github.com/elastic/elasticsearch-net/tree/master/src/Tests/Tests/QueryDsl/Specialized/RankFeature/RankFeatureQueryUsageTests.cs. 
+If you wish to submit a PR for any spelling mistakes, typos or grammatical errors for this file,
+please modify the original csharp file found at the link and submit the PR with that change. Thanks!
+////
+
+[[rank-feature-query-usage]]
+=== Rank Feature Query Usage
+
+The rank_feature query is a specialized query that only works on `rank_feature` fields and `rank_features` fields.
+Its goal is to boost the score of documents based on the values of numeric features. It is typically put in a should clause of a bool query
+so that its score is added to the score of the query.
+
+Compared to using `function_score` or other ways to modify the score, this query has the benefit of being able to efficiently
+skip non-competitive hits when track_total_hits is not set to true. Speedups may be spectacular.
+
+See the Elasticsearch documentation on {ref_current}/query-dsl-rank-feature-query.html[rank feature query] for more details.
+
+==== Fluent DSL example
+
+[source,csharp]
+----
+q
+.RankFeature(rf => rf
+    .Name("named_query")
+    .Boost(1.1)
+    .Field(f => f.Rank)
+    .Saturation()
+)
+----
+
+==== Object Initializer syntax example
+
+[source,csharp]
+----
+new RankFeatureQuery()
+{
+    Name = "named_query",
+    Boost = 1.1, 
+    Field = Infer.Field<Project>(f => f.Rank),
+    Function = new RankFeatureSaturationFunction()
+}
+----
+
+[source,javascript]
+.Example json output
+----
+{
+  "rank_feature": {
+    "_name": "named_query",
+    "boost": 1.1,
+    "field": "rank",
+    "saturation": {}
+  }
+}
+----
+

src/Nest/Mapping/Types/Core/RankFeature/RankFeatureAttribute.cs

@@ -0,0 +1,19 @@
+namespace Nest
+{
+	/// <inheritdoc cref="IRankFeatureProperty"/>
+	public class RankFeatureAttribute : ElasticsearchPropertyAttributeBase, IRankFeatureProperty
+	{
+		public RankFeatureAttribute() : base(FieldType.RankFeature) { }
+
+		private IRankFeatureProperty Self => this;
+
+		/// <inheritdoc cref="IRankFeatureProperty.PositiveScoreImpact"/>
+		public bool PositiveScoreImpact
+		{
+			get => Self.PositiveScoreImpact.GetValueOrDefault(true);
+			set => Self.PositiveScoreImpact = value;
+		}
+
+		bool? IRankFeatureProperty.PositiveScoreImpact { get; set; }
+	}
+}

src/Nest/Mapping/Types/Core/RankFeature/RankFeatureProperty.cs

@@ -0,0 +1,48 @@
+using System.Diagnostics;
+using System.Runtime.Serialization;
+using Elasticsearch.Net.Utf8Json;
+
+namespace Nest
+{
+	/// <summary>
+	/// A field that can index numbers so that they can later be used
+	/// to boost documents in queries with a rank_feature query.
+	/// </summary>
+	[InterfaceDataContract]
+	public interface IRankFeatureProperty : IProperty
+	{
+		/// <summary>
+		/// Rank features that correlate negatively with the score should set <see cref="PositiveScoreImpact"/>
+		/// to false (defaults to true). This will be used by the rank_feature query to modify the scoring
+		/// formula in such a way that the score decreases with the value of the feature instead of
+		/// increasing. For instance in web search, the url length is a commonly used feature
+		/// which correlates negatively with scores.
+		/// </summary>
+		[DataMember(Name = "positive_score_impact")]
+		bool? PositiveScoreImpact { get; set; }
+	}
+
+	/// <inheritdoc cref="IRankFeatureProperty" />
+	public class RankFeatureProperty : PropertyBase, IRankFeatureProperty
+	{
+		public RankFeatureProperty() : base(FieldType.RankFeature) { }
+
+		/// <inheritdoc />
+		public bool? PositiveScoreImpact { get; set; }
+	}
+
+	/// <inheritdoc cref="IRankFeatureProperty" />
+	[DebuggerDisplay("{DebugDisplay}")]
+	public class RankFeaturePropertyDescriptor<T>
+		: PropertyDescriptorBase<RankFeaturePropertyDescriptor<T>, IRankFeatureProperty, T>, IRankFeatureProperty
+		where T : class
+	{
+		public RankFeaturePropertyDescriptor() : base(FieldType.RankFeature) { }
+
+		bool? IRankFeatureProperty.PositiveScoreImpact { get; set; }
+
+		/// <inheritdoc cref="IRankFeatureProperty.PositiveScoreImpact" />
+		public RankFeaturePropertyDescriptor<T> PositiveScoreImpact(bool? positiveScoreImpact = true) =>
+			Assign(positiveScoreImpact, (a, v) => a.PositiveScoreImpact = v);
+	}
+}

src/Nest/Mapping/Types/Core/RankFeatures/RankFeaturesAttribute.cs

@@ -0,0 +1,8 @@
+namespace Nest
+{
+	/// <inheritdoc cref="IRankFeaturesProperty"/>
+	public class RankFeaturesAttribute : ElasticsearchPropertyAttributeBase, IRankFeaturesProperty
+	{
+		public RankFeaturesAttribute() : base(FieldType.RankFeatures) { }
+	}
+}

src/Nest/Mapping/Types/Core/RankFeatures/RankFeaturesProperty.cs

@@ -0,0 +1,31 @@
+using System.Diagnostics;
+using System.Runtime.Serialization;
+using Elasticsearch.Net.Utf8Json;
+
+namespace Nest
+{
+	/// <summary>
+	/// A field that can index numeric feature vectors, so that they can later be used to boost documents in queries with a rank_feature query.
+	/// It is analogous to the <see cref="IRankFeatureProperty"/> datatype, but is better suited when the list of features is sparse so that it
+	/// wouldn't be reasonable to add one field to the mappings for each of them.
+	/// </summary>
+	[InterfaceDataContract]
+	public interface IRankFeaturesProperty : IProperty
+	{
+	}
+
+	/// <inheritdoc cref="IRankFeaturesProperty" />
+	public class RankFeaturesProperty : PropertyBase, IRankFeaturesProperty
+	{
+		public RankFeaturesProperty() : base(FieldType.RankFeatures) { }
+	}
+
+	/// <inheritdoc cref="IRankFeaturesProperty" />
+	[DebuggerDisplay("{DebugDisplay}")]
+	public class RankFeaturesPropertyDescriptor<T>
+		: PropertyDescriptorBase<RankFeaturesPropertyDescriptor<T>, IRankFeaturesProperty, T>, IRankFeaturesProperty
+		where T : class
+	{
+		public RankFeaturesPropertyDescriptor() : base(FieldType.RankFeatures) { }
+	}
+}

src/Nest/Mapping/Types/FieldType.cs

@@ -118,5 +118,11 @@ public enum FieldType
 
 		[EnumMember(Value = "join")]
 		Join,
+
+		[EnumMember(Value = "rank_feature")]
+		RankFeature,
+
+		[EnumMember(Value = "rank_features")]
+		RankFeatures
 	}
 }

src/Nest/Mapping/Types/Properties.cs

@@ -154,6 +154,12 @@ public PropertiesDescriptor<T> Object<TChild>(Func<ObjectTypeDescriptor<T, TChil
 
 		public PropertiesDescriptor<T> FieldAlias(Func<FieldAliasPropertyDescriptor<T>, IFieldAliasProperty> selector) => SetProperty(selector);
 
+		/// <inheritdoc cref="IRankFeatureProperty"/>
+		public PropertiesDescriptor<T> RankFeature(Func<RankFeaturePropertyDescriptor<T>, IRankFeatureProperty> selector) => SetProperty(selector);
+
+		/// <inheritdoc cref="IRankFeaturesProperty"/>
+		public PropertiesDescriptor<T> RankFeatures(Func<RankFeaturesPropertyDescriptor<T>, IRankFeaturesProperty> selector) => SetProperty(selector);
+
 		public PropertiesDescriptor<T> Custom(IProperty customType) => SetProperty(customType);
 
 		private PropertiesDescriptor<T> SetProperty<TDescriptor, TInterface>(Func<TDescriptor, TInterface> selector)

src/Nest/Mapping/Types/PropertyBase.cs

@@ -23,7 +23,7 @@ public interface IProperty : IFieldMapping
 		/// <summary>
 		/// The name of the property
 		/// </summary>
-		//[DataMember(Name = "name")]
+		[IgnoreDataMember]
 		PropertyName Name { get; set; }
 
 		/// <summary>