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Aggregate Queries

Dgraph automatically generates aggregate queries for GraphQL schemas. Aggregate queries fetch aggregate data, including the following:

  • Count queries that let you count fields satisfying certain criteria specified using a filter.
  • Advanced aggregate queries that let you calculate the maximum, minimum, sum and average of specified fields.

Aggregate queries are compatible with the @auth directive and follow the same authorization rules as the query keyword. You can also use filters with aggregate queries, as shown in some of the examples provided below.

Count queries at root

For every type defined in a GraphQL schema, Dgraph generates an aggregate query aggregate<type name>. This query includes a count field, as well as advanced aggregate query fields.

Examples

Example: Fetch the total number of posts.

   query {
     aggregatePost {
       count
     }
   }

Example: Fetch the number of posts whose titles contain GraphQL.

   query {
     aggregatePost(filter: {
       title: {
         anyofterms: "GraphQL"
         }
       }) {
       count
     }
   }

Count queries for child nodes

Dgraph also defines <field name>Aggregate fields for every field which is of type List[Type/Interface] inside query<type name> queries, allowing you to do a count on fields, or to use the advanced aggregate queries.

Examples

Example: Fetch the number of posts for all authors along with their name.

   query {
     queryAuthor {
       name
       postsAggregate {
        count
       }
     }
   }

Example: Fetch the number of posts with a score greater than 10 for all authors, along with their name

   query {
     queryAuthor {
       name
       postsAggregate(filter: {
         score: {
           gt: 10
         }
       }) {
        count
      }
    }
  }

Advanced aggregate queries at root

For every type defined in the GraphQL schema, Dgraph generates an aggregate query aggregate<type name> that includes advanced aggregate query fields, and also includes a count field (see Count queries at root). Dgraph generates one or more advanced aggregate query fields (<field-name>Min, <field-name>Max, <field-name>Sum and <field-name>Avg) for fields in the schema that are typed as Int, Float, String and Datetime.

Note Advanced aggregate query fields are generated according to a field’s type. Fields typed as Int and Float get the following query fields: <field name>Max, <field name>Min, <field name>Sum and <field name>Avg. Fields typed as String and Datetime only get the <field name>Max, <field name>Min query fields.

Examples

Example: Fetch the average number of posts written by authors:

   query {
     aggregateAuthor {
       numPostsAvg
     }
   }

Example: Fetch the total number of posts by all authors, and the maximum number of posts by any single Author:

   query {
     aggregateAuthor {
       numPostsSum
       numPostsMax
     }
   }

Example: Fetch the average number of posts for authors with more than 20 friends:

   query {
     aggregateAuthor (filter: {
       friends: {
         gt: 20
       }
     }) {
       numPostsAvg
     }
   }

Advanced aggregate queries for child nodes

Dgraph also defines aggregate <field name>Aggregate fields for child nodes within query<type name> queries. This is done for each field that is of type List[Type/Interface] inside query<type name> queries, letting you fetch minimums, maximums, averages and sums for those fields.

Note Aggregate query fields are generated according to a field’s type. Fields typed as Int and Float get the following query fields:<field name>Max, <field name>Min, <field name>Sum and <field name>Avg. Fields typed as String and Datetime only get the <field name>Max, <field name>Min query fields.

Examples

Example: Fetch the minimum, maximum and average score of the posts for each Author, along with each author’s name.

   query {
     queryAuthor {
       name
       postsAggregate {
         scoreMin
         scoreMax
         scoreAvg
       }
     }
   }

Example: Fetch the date of the most recent post with a score greater than 10 for all authors, along with the author’s name.

   query {
     queryAuthor {
       name
       postsAggregate(filter: {
         score: {
           gt: 10
         }
       }) {
         datePublishedMax
      }
    }
  }

Aggregate queries on null data

Aggregate queries against empty data return null. This is true for both the <field name>Aggregate fields and aggregate<type name> queries generated by Dgraph.

So, in the examples above, the following is true:

  • If there are no nodes of type Author, the aggregateAuthor query will return null.
  • If an Author has not written any posts, the field postsAggregate will be null for that Author.