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Interfaces

Interfaces can be used in GraphQL to predefine a set of fields and their types that can then be implemented in other object types. When an object types implements an interface, it has to implement all the fields of the interface, otherwise an error is raised during the schema validation phase.

If you have multiple variations of an object type in your application, you can use an interface to define the common fields. For example, if you are building a web application with a CMS and several objects that should have meta data attached for SEO purposes, you could create a CMS_PageInterface as follows:

interface CMS_PageInterface {
    # The following fields will be required by all types that implement the interface:
    title: String!
    description: String!
    slug: String! @unique
}

type CMS_Article implements CMS_PageInterface & Node {
    # Required field from Node interface
    id: ID!

    # Fields from CMS_PageInterface
    title: String!
    description: String!
    slug: String! @unique

    # Custom fields that are only part of CMS_Article
    text: String
    category: CMS_Category
}

type CMS_Category implements CMS_PageInterface & Node {
    # Required field from Node interface
    id: ID!

    # Fields from CMS_PageInterface
    title: String!
    description: String!
    slug: String! @unique
}

Both the CMS_Article type and the CMS_Category implement the CMS_PageInterface which guarantees that they implement all the fields that are part of the interface. If a field is missing or has a wrong type, an error will be raised during the validation phase of the schema.

You can reuse any interface that is part of your application, also across multiple modules.

A type can implement multiple interfaces which would have to be separated by &. The above example implements the CMS_PageInterface and the Node interfaces.

Builtin Interface

Slicknode comes with several builtin interfaces that are used to enable special functionality:

  • Node: Types that implement the Node interface are persisted to a data store and can also be refetched by its ID via the root query type.
  • TimeStampedInterface: Interface to automatically add the current timestamp on update and creation