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Composite Aggregation Usage

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Composite Aggregation Usage

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A multi-bucket aggregation that creates composite buckets from different sources.

Unlike the other multi-bucket aggregation the composite aggregation can be used to paginate all buckets from a multi-level aggregation efficiently. This aggregation provides a way to stream all buckets of a specific aggregation similarly to what scroll does for documents.

The composite buckets are built from the combinations of the values extracted/created for each document and each combination is considered as a composite bucket.

Only available in Elasticsearch 6.1.0+

Be sure to read the Elasticsearch documentation on Composite Aggregation.

Fluent DSL example

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a => a
.Composite("my_buckets", date => date
    .Sources(s => s
        .Terms("branches", t => t
            .Field(f => f.Branches.Suffix("keyword"))
        )
        .DateHistogram("started", d => d
            .Field(f => f.StartedOn)
            .Interval(DateInterval.Month)
        )
        .Histogram("branch_count", h => h
            .Field(f => f.RequiredBranches)
            .Interval(1)
        )
    )
    .Aggregations(childAggs => childAggs
        .Nested("project_tags", n => n
            .Path(p => p.Tags)
            .Aggregations(nestedAggs => nestedAggs
                .Terms("tags", avg => avg.Field(p => p.Tags.First().Name))
            )
        )
    )
)

Object Initializer syntax example

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new CompositeAggregation("my_buckets")
{
    Sources = new List<ICompositeAggregationSource>
    {
        new TermsCompositeAggregationSource("branches")
        {
            Field = Field<Project>(f => f.Branches.Suffix("keyword"))
        },
        new DateHistogramCompositeAggregationSource("started")
        {
            Field = Field<Project>(f => f.StartedOn),
            Interval = DateInterval.Month
        },
        new HistogramCompositeAggregationSource("branch_count")
        {
            Field = Field<Project>(f => f.RequiredBranches),
            Interval = 1
        }
    },
    Aggregations = new NestedAggregation("project_tags")
    {
        Path = Field<Project>(p => p.Tags),
        Aggregations = new TermsAggregation("tags")
        {
            Field = Field<Project>(p => p.Tags.First().Name)
        }
    }
}

Example json output.

{
  "my_buckets": {
    "composite": {
      "sources": [
        {
          "branches": {
            "terms": {
              "field": "branches.keyword"
            }
          }
        },
        {
          "started": {
            "date_histogram": {
              "field": "startedOn",
              "interval": "month"
            }
          }
        },
        {
          "branch_count": {
            "histogram": {
              "field": "requiredBranches",
              "interval": 1.0
            }
          }
        }
      ]
    },
    "aggs": {
      "project_tags": {
        "nested": {
          "path": "tags"
        },
        "aggs": {
          "tags": {
            "terms": {
              "field": "tags.name"
            }
          }
        }
      }
    }
  }
}

Handling Responses

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Each Composite aggregation bucket key is a CompositeKey type, a specialized IReadOnlyDictionary<string, object> type with methods to convert values to supported types

response.ShouldBeValid();

var composite = response.Aggregations.Composite("my_buckets");
composite.Should().NotBeNull();
composite.Buckets.Should().NotBeNullOrEmpty();

if (TestConfiguration.Instance.InRange(">=6.3.0"))
{
    composite.AfterKey.Should().NotBeNull();
    composite.AfterKey.Should()
        .HaveCount(3)
        .And.ContainKeys("branches", "started", "branch_count");
}

foreach (var item in composite.Buckets)
{
    var key = item.Key;
    key.Should().NotBeNull();

    key.TryGetValue("branches", out string branches).Should().BeTrue();
    branches.Should().NotBeNullOrEmpty();

    key.TryGetValue("started", out DateTime started).Should().BeTrue();
    started.Should().BeAfter(default(DateTime));

    key.TryGetValue("branch_count", out int branchCount).Should().BeTrue();
    branchCount.Should().BeGreaterThan(0);

    item.DocCount.Should().BeGreaterThan(0);

    var nested = item.Nested("project_tags");
    nested.Should().NotBeNull();

    if (nested.DocCount > 0)
    {
        var nestedTerms = nested.Terms("tags");
        nestedTerms.Buckets.Count.Should().BeGreaterThan(0);
    }
}

Missing buckets

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By default documents without a value for a given source are ignored. It is possible to include them in the response by setting missing_bucket to true (defaults to false):

Only available in Elasticsearch 6.4.0+

Fluent DSL example

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a => a
.Composite("my_buckets", date => date
    .Sources(s => s
        .Terms("branches", t => t
            .Field(f => f.Branches.Suffix("keyword"))
            .MissingBucket()
            .Order(SortOrder.Ascending)
        )
    )
    .Aggregations(childAggs => childAggs
        .Nested("project_tags", n => n
            .Path(p => p.Tags)
            .Aggregations(nestedAggs => nestedAggs
                .Terms("tags", avg => avg.Field(p => p.Tags.First().Name))
            )
        )
    )
)

Object Initializer syntax example

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new CompositeAggregation("my_buckets")
{
    Sources = new List<ICompositeAggregationSource>
    {
        new TermsCompositeAggregationSource("branches")
        {
            Field = Field<Project>(f => f.Branches.Suffix("keyword")),
            MissingBucket = true,
            Order = SortOrder.Ascending
        }
    },
    Aggregations = new NestedAggregation("project_tags")
    {
        Path = Field<Project>(p => p.Tags),
        Aggregations = new TermsAggregation("tags")
        {
            Field = Field<Project>(p => p.Tags.First().Name)
        }
    }
}

Example json output.

{
  "my_buckets": {
    "composite": {
      "sources": [
        {
          "branches": {
            "terms": {
              "field": "branches.keyword",
              "order": "asc",
              "missing_bucket": true
            }
          }
        }
      ]
    },
    "aggs": {
      "project_tags": {
        "nested": {
          "path": "tags"
        },
        "aggs": {
          "tags": {
            "terms": {
              "field": "tags.name"
            }
          }
        }
      }
    }
  }
}

Handling Responses

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Each Composite aggregation bucket key is an CompositeKey, a specialized IReadOnlyDictionary<string, object> type with methods to convert values to supported types

response.ShouldBeValid();

var composite = response.Aggregations.Composite("my_buckets");
composite.Should().NotBeNull();
composite.Buckets.Should().NotBeNullOrEmpty();
composite.AfterKey.Should().NotBeNull();

if (TestConfiguration.Instance.InRange(">=6.3.0"))
    composite.AfterKey.Should().HaveCount(1).And.ContainKeys("branches");

var i = 0;
foreach (var item in composite.Buckets)
{
    var key = item.Key;
    key.Should().NotBeNull();

    key.TryGetValue("branches", out string branches).Should().BeTrue("expected to find 'branches' in composite bucket");
    if (i == 0) branches.Should().BeNull("First key should be null as we expect to have some projects with no branches");
    else branches.Should().NotBeNullOrEmpty();

    var nested = item.Nested("project_tags");
    nested.Should().NotBeNull();

    var nestedTerms = nested.Terms("tags");
    nestedTerms.Buckets.Count.Should().BeGreaterThan(0);
    i++;
}

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