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GraphQL on Existing Dgraph

How to use GraphQL on an existing Dgraph instance

In the case where you have an existing Dgraph instance which has been created using a DQL Schema (and populated with Dgraph import tools) and you want to expose some or all of the data using a GraphQL API, you can use the @dgraph directive to customize how Dgraph maps GraphQL type names and fields names to DQL types and predicates.

Language support in GraphQL

In your GraphQL schema, you need to define a field for each language that you want to use. In addition, you also need to apply the @dgraph(pred: "...") directive on that field, with the pred argument set to point to the correct DQL predicate with a language tag for the language that you want to use it for. Dgraph will automatically add a @lang directive in the DQL schema for the corresponding predicate.

Tip By default, the DQL predicate for a GraphQL field is generated as Typename.FieldName.

For example:

type Person {
     name: String   # is the auto-generated DQL predicate for this GraphQL field, unless overridden using @dgraph(pred: "...")
     nameHi: String @dgraph(pred:"") # this field exposes the value for the language tag `@hi` for the DQL predicate `` to GraphQL
     nameEn: String @dgraph(pred:"")
     nameHi_En:  String @dgraph(pred:"") # this field uses multiple language tags: `@hi` and `@en`
     nameHi_En_untag:  String @dgraph(pred:"") # as this uses `.`, it will give untagged values if there is no value for `@hi` or `@en`

If a GraphQL field uses more than one language tag, then it won’t be part of any mutation input. Like, in the above example the fields nameHi_En and nameHi_En_untag can’t be given as an input to any mutation. Only the fields which use one or no language can be given in a mutation input, like name, nameHi, and nameEn.

All the fields can be queried, irrespective of whether they use one language or more.

Note GraphQL won’t be able to query* type of language tags because of the structural requirements of GraphQL.