Add Parent Aggregation

Relates: elastic/elasticsearch#34210

This commit adds Parent Aggregation to the high level client.

docs/aggregations.asciidoc

@@ -138,6 +138,8 @@ In addition to the buckets themselves, the bucket aggregations also compute and
 
 * <<nested-aggregation-usage,Nested Aggregation Usage>>
 
+* <<parent-aggregation-usage,Parent Aggregation Usage>>
+
 * <<range-aggregation-usage,Range Aggregation Usage>>
 
 * <<reverse-nested-aggregation-usage,Reverse Nested Aggregation Usage>>
@@ -193,6 +195,8 @@ include::aggregations/bucket/missing/missing-aggregation-usage.asciidoc[]
 
 include::aggregations/bucket/nested/nested-aggregation-usage.asciidoc[]
 
+include::aggregations/bucket/parent/parent-aggregation-usage.asciidoc[]
+
 include::aggregations/bucket/range/range-aggregation-usage.asciidoc[]
 
 include::aggregations/bucket/reverse-nested/reverse-nested-aggregation-usage.asciidoc[]

docs/aggregations/bucket/parent/parent-aggregation-usage.asciidoc

@@ -0,0 +1,98 @@
+:ref_current: https://www.elastic.co/guide/en/elasticsearch/reference/6.5
+
+: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/6.x/src/Tests/Tests/Aggregations/Bucket/Parent/ParentAggregationUsageTests.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!
+////
+
+[[parent-aggregation-usage]]
+=== Parent Aggregation Usage
+
+A special single bucket aggregation that selects parent documents that have the specified type, as defined in a `join` field.
+
+Be sure to read the Elasticsearch documentation on {ref_current}/search-aggregations-bucket-parent-aggregation.html[Parent Aggregation].
+
+==== Fluent DSL example
+
+[source,csharp]
+----
+a => a
+.Parent<Project>("name_of_parent_agg", parent => parent <1>
+    .Aggregations(parentAggs => parentAggs
+        .Average("average_commits", avg => avg.Field(p => p.NumberOfCommits))
+        .Max("max_commits", avg => avg.Field(p => p.NumberOfCommits))
+        .Min("min_commits", avg => avg.Field(p => p.NumberOfCommits))
+    )
+)
+----
+<1> sub-aggregations are on the type determined from the generic type parameter. In this example, the search is against `CommitActivity` type and `Project` is a parent of `CommitActivity`
+
+==== Object Initializer syntax example
+
+[source,csharp]
+----
+new ParentAggregation("name_of_parent_agg", typeof(CommitActivity)) <1>
+{
+    Aggregations =
+        new AverageAggregation("average_commits", Field<Project>(f => f.NumberOfCommits)) <2>
+        && new MaxAggregation("max_commits", Field<Project>(f => f.NumberOfCommits))
+        && new MinAggregation("min_commits", Field<Project>(f => f.NumberOfCommits))
+}
+----
+<1> `join` field is determined from the _child_ type. In this example, it is `CommitActivity`
+
+<2> sub-aggregations are on the type determined from the `join` field. In this example, a `Project` is a parent of `CommitActivity`
+
+[source,javascript]
+.Example json output
+----
+{
+  "size": 0,
+  "aggs": {
+    "name_of_parent_agg": {
+      "parent": {
+        "type": "commits"
+      },
+      "aggs": {
+        "average_commits": {
+          "avg": {
+            "field": "numberOfCommits"
+          }
+        },
+        "max_commits": {
+          "max": {
+            "field": "numberOfCommits"
+          }
+        },
+        "min_commits": {
+          "min": {
+            "field": "numberOfCommits"
+          }
+        }
+      }
+    }
+  }
+}
+----
+
+==== Handling Responses
+
+[source,csharp]
+----
+response.ShouldBeValid();
+
+var parentAgg = response.Aggregations.Parent("name_of_parent_agg");
+parentAgg.Should().NotBeNull();
+parentAgg.DocCount.Should().BeGreaterThan(0);
+parentAgg.Min("average_commits").Should().NotBeNull();
+parentAgg.Min("min_commits").Should().NotBeNull();
+parentAgg.Max("max_commits").Should().NotBeNull();
+----
+

src/Nest/Aggregations/AggregateDictionary.cs

@@ -113,6 +113,8 @@ public FiltersAggregate Filters(string key)
 
 		public SingleBucketAggregate Children(string key) => TryGet<SingleBucketAggregate>(key);
 
+		public SingleBucketAggregate Parent(string key) => TryGet<SingleBucketAggregate>(key);
+
 		public SingleBucketAggregate Sampler(string key) => TryGet<SingleBucketAggregate>(key);
 
 		public GeoCentroidAggregate GeoCentroid(string key) => TryGet<GeoCentroidAggregate>(key);

src/Nest/Aggregations/AggregationContainer.cs

@@ -177,6 +177,9 @@ public interface IAggregationContainer
 		[JsonProperty("nested")]
 		INestedAggregation Nested { get; set; }
 
+		[JsonProperty("parent")]
+		IParentAggregation Parent { get; set; }
+
 		[JsonProperty("percentile_ranks")]
 		IPercentileRanksAggregation PercentileRanks { get; set; }
 
@@ -304,6 +307,8 @@ public class AggregationContainer : IAggregationContainer
 
 		public INestedAggregation Nested { get; set; }
 
+		public IParentAggregation Parent { get; set; }
+
 		public IPercentileRanksAggregation PercentileRanks { get; set; }
 
 		public IPercentilesAggregation Percentiles { get; set; }
@@ -440,6 +445,8 @@ public class AggregationContainerDescriptor<T> : DescriptorBase<AggregationConta
 
 		INestedAggregation IAggregationContainer.Nested { get; set; }
 
+		IParentAggregation IAggregationContainer.Parent { get; set; }
+
 		IPercentileRanksAggregation IAggregationContainer.PercentileRanks { get; set; }
 
 		IPercentilesAggregation IAggregationContainer.Percentiles { get; set; }
@@ -582,6 +589,11 @@ Func<NestedAggregationDescriptor<T>, INestedAggregation> selector
 		) =>
 			_SetInnerAggregation(name, selector, (a, d) => a.Nested = d);
 
+		public AggregationContainerDescriptor<T> Parent<TParent>(string name,
+			Func<ParentAggregationDescriptor<T, TParent>, IParentAggregation> selector
+		) where TParent : class =>
+			_SetInnerAggregation(name, selector, (a, d) => a.Parent = d);
+
 		public AggregationContainerDescriptor<T> ReverseNested(string name,
 			Func<ReverseNestedAggregationDescriptor<T>, IReverseNestedAggregation> selector
 		) =>

src/Nest/Aggregations/Bucket/Parent/ParentAggregation.cs

@@ -0,0 +1,40 @@
+using Newtonsoft.Json;
+
+namespace Nest
+{
+	[JsonObject(MemberSerialization = MemberSerialization.OptIn)]
+	[ContractJsonConverter(typeof(AggregationJsonConverter<ParentAggregation>))]
+	public interface IParentAggregation : IBucketAggregation
+	{
+		/// <summary>
+		/// The type for the child in the parent/child relationship
+		/// </summary>
+		[JsonProperty("type")]
+		RelationName Type { get; set; }
+	}
+
+	public class ParentAggregation : BucketAggregationBase, IParentAggregation
+	{
+		internal ParentAggregation() { }
+
+		public ParentAggregation(string name, RelationName type) : base(name) => Type = type;
+
+		public RelationName Type { get; set; }
+
+		internal override void WrapInContainer(AggregationContainer c) => c.Parent = this;
+	}
+
+	public class ParentAggregationDescriptor<T, TParent>
+		: BucketAggregationDescriptorBase<ParentAggregationDescriptor<T, TParent>, IParentAggregation, TParent>, IParentAggregation
+		where T : class
+		where TParent : class
+	{
+		RelationName IParentAggregation.Type { get; set; } = typeof(T);
+
+		public ParentAggregationDescriptor<T, TParent> Type(RelationName type) =>
+			Assign(a => a.Type = type);
+
+		public ParentAggregationDescriptor<T, TParent> Type<TOtherParent>() =>
+			Assign(a => a.Type = typeof(TOtherParent));
+	}
+}

src/Nest/Aggregations/Visitor/AggregationVisitor.cs

@@ -66,6 +66,8 @@ public interface IAggregationVisitor
 
 		void Visit(INestedAggregation aggregation);
 
+		void Visit(IParentAggregation aggregation);
+
 		void Visit(IReverseNestedAggregation aggregation);
 
 		void Visit(IRangeAggregation aggregation);
@@ -149,6 +151,7 @@ public virtual void Visit(IReverseNestedAggregation aggregation) { }
 
 		public virtual void Visit(ITermsAggregation aggregation) { }
 
+		// TODO: make virtual
 		public void Visit(ISignificantTextAggregation aggregation) { }
 
 		public virtual void Visit(IPercentileRanksAggregation aggregation) { }
@@ -195,6 +198,8 @@ public virtual void Visit(IRangeAggregation aggregation) { }
 
 		public virtual void Visit(INestedAggregation aggregation) { }
 
+		public virtual void Visit(IParentAggregation aggregation) { }
+
 		public virtual void Visit(ICardinalityAggregation aggregation) { }
 
 		public virtual void Visit(IGlobalAggregation aggregation) { }

src/Nest/Aggregations/Visitor/AggregationWalker.cs

@@ -111,6 +111,11 @@ public void Walk(IAggregationContainer aggregation, IAggregationVisitor visitor)
 				v.Visit(d);
 				Accept(v, d.Aggregations);
 			});
+			AcceptAggregation(aggregation.Parent, visitor, (v, d) =>
+			{
+				v.Visit(d);
+				Accept(v, d.Aggregations);
+			});
 			AcceptAggregation(aggregation.PercentileRanks, visitor, (v, d) => v.Visit(d));
 			AcceptAggregation(aggregation.Percentiles, visitor, (v, d) => v.Visit(d));
 			AcceptAggregation(aggregation.Range, visitor, (v, d) =>

src/Tests/Tests/Aggregations/Bucket/Parent/ParentAggregationUsageTests.cs

@@ -0,0 +1,131 @@
+using System;
+using System.Threading.Tasks;
+using Elastic.Xunit.XunitPlumbing;
+using Elasticsearch.Net;
+using FluentAssertions;
+using Nest;
+using Tests.Core.Client;
+using Tests.Core.Extensions;
+using Tests.Core.ManagedElasticsearch.Clusters;
+using Tests.Core.ManagedElasticsearch.NodeSeeders;
+using Tests.Domain;
+using Tests.Framework;
+using Tests.Framework.Integration;
+using static Nest.Infer;
+
+namespace Tests.Aggregations.Bucket.Parent
+{
+	/**
+	 * A special single bucket aggregation that selects parent documents that have the specified type, as defined in a `join` field.
+	 *
+	 * Be sure to read the Elasticsearch documentation on {ref_current}/search-aggregations-bucket-parent-aggregation.html[Parent Aggregation].
+	 */
+	public class ParentAggregationUsageTests : ApiIntegrationTestBase<ReadOnlyCluster, ISearchResponse<CommitActivity>, ISearchRequest, SearchDescriptor<CommitActivity>, SearchRequest<CommitActivity>>
+	{
+		public ParentAggregationUsageTests(ReadOnlyCluster i, EndpointUsage usage) : base(i, usage) { }
+
+		protected override bool ExpectIsValid => true;
+
+		protected sealed override object ExpectJson => new
+		{
+			size = 0,
+			aggs = new
+			{
+				name_of_parent_agg = new
+				{
+					parent = new { type = "commits" },
+					aggs = new
+					{
+						average_commits = new
+						{
+							avg = new { field = "numberOfCommits" }
+						},
+						max_commits = new
+						{
+							max = new { field = "numberOfCommits" }
+						},
+						min_commits = new
+						{
+							min = new { field = "numberOfCommits" }
+						}
+					}
+				}
+			}
+		};
+
+		protected override int ExpectStatusCode => 200;
+
+		// hide
+		protected override Func<SearchDescriptor<CommitActivity>, ISearchRequest> Fluent => s => s
+			.Size(0)
+			.Index(DefaultSeeder.CommitsAliasFilter)
+			.Type<CommitActivity>()
+			.TypedKeys(TestClient.Configuration.Random.TypedKeys)
+			.Aggregations(FluentAggs);
+
+		protected override HttpMethod HttpMethod => HttpMethod.POST;
+
+		// hide
+		protected override SearchRequest<CommitActivity> Initializer =>
+			new SearchRequest<CommitActivity>(DefaultSeeder.CommitsAliasFilter, Type<CommitActivity>())
+			{
+				Size = 0,
+				TypedKeys = TestClient.Configuration.Random.TypedKeys,
+				Aggregations = InitializerAggs
+			};
+
+		protected override string UrlPath => $"/commits-only/doc/_search";
+
+		// https://youtrack.jetbrains.com/issue/RIDER-19912
+		[U] protected override Task HitsTheCorrectUrl() => base.HitsTheCorrectUrl();
+
+		[U] protected override Task UsesCorrectHttpMethod() => base.UsesCorrectHttpMethod();
+
+		[U] protected override void SerializesInitializer() => base.SerializesInitializer();
+
+		[U] protected override void SerializesFluent() => base.SerializesFluent();
+
+		[I] public override Task ReturnsExpectedStatusCode() => base.ReturnsExpectedResponse();
+
+		[I] public override Task ReturnsExpectedIsValid() => base.ReturnsExpectedIsValid();
+
+		[I] public override Task ReturnsExpectedResponse() => base.ReturnsExpectedResponse();
+
+		protected override LazyResponses ClientUsage() => Calls(
+			(client, f) => client.Search<CommitActivity>(f),
+			(client, f) => client.SearchAsync<CommitActivity>(f),
+			(client, r) => client.Search<CommitActivity>(r),
+			(client, r) => client.SearchAsync<CommitActivity>(r)
+		);
+
+		protected Func<AggregationContainerDescriptor<CommitActivity>, IAggregationContainer> FluentAggs => a => a
+			.Parent<Project>("name_of_parent_agg", parent => parent // <1> sub-aggregations are on the type determined from the generic type parameter. In this example, the search is against `CommitActivity` type and `Project` is a parent of `CommitActivity`
+				.Aggregations(parentAggs => parentAggs
+					.Average("average_commits", avg => avg.Field(p => p.NumberOfCommits))
+					.Max("max_commits", avg => avg.Field(p => p.NumberOfCommits))
+					.Min("min_commits", avg => avg.Field(p => p.NumberOfCommits))
+				)
+			);
+
+		protected AggregationDictionary InitializerAggs =>
+			new ParentAggregation("name_of_parent_agg", typeof(CommitActivity)) // <1> `join` field is determined from the _child_ type. In this example, it is `CommitActivity`
+			{
+				Aggregations =
+					new AverageAggregation("average_commits", Field<Project>(f => f.NumberOfCommits)) // <2> sub-aggregations are on the type determined from the `join` field. In this example, a `Project` is a parent of `CommitActivity`
+					&& new MaxAggregation("max_commits", Field<Project>(f => f.NumberOfCommits))
+					&& new MinAggregation("min_commits", Field<Project>(f => f.NumberOfCommits))
+			};
+
+		protected override void ExpectResponse(ISearchResponse<CommitActivity> response)
+		{
+			response.ShouldBeValid();
+
+			var parentAgg = response.Aggregations.Parent("name_of_parent_agg");
+			parentAgg.Should().NotBeNull();
+			parentAgg.DocCount.Should().BeGreaterThan(0);
+			parentAgg.Min("average_commits").Should().NotBeNull();
+			parentAgg.Min("min_commits").Should().NotBeNull();
+			parentAgg.Max("max_commits").Should().NotBeNull();
+		}
+	}
+}