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109 lines
3.0 KiB
Markdown
109 lines
3.0 KiB
Markdown
---
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title: Enums, unions, and interfaces
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summary: Add some non-object types to your schema
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---
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# Working with generic types
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[CHILDREN asList]
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[alert]
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You are viewing docs for a pre-release version of silverstripe/graphql (4.x).
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Help us improve it by joining #graphql on the [Community Slack](https://www.silverstripe.org/blog/community-slack-channel/),
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and report any issues at [github.com/silverstripe/silverstripe-graphql](https://github.com/silverstripe/silverstripe-graphql).
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Docs for the current stable version (3.x) can be found
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[here](https://github.com/silverstripe/silverstripe-graphql/tree/3)
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[/alert]
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## Enums, unions, and interfaces
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In more complex schemas, you may want to define types that aren't simply a list of fields, or
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"object types." These include enums, unions and interfaces.
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### Enum types
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Enum types are simply a list of string values that are possible for a given field. They are
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often used in arguments to queries, such as `{sort: DESC }`.
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It's very easy to add enum types to your schema. Just use the `enums` section of the config.
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**app/_graphql/schema.yml**
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```yaml
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enums:
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SortDirection:
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DESC: Descending order
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ASC: Ascending order
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```
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### Interfaces
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An interface is a specification of fields that must be included on a type that implements it.
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For example, an interface `Person` could include `firstName: String`, `surname: String`, and
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`age: Int`. The types `Actor` and `Chef` would implement the `Person` interface. Actors and
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chefs must have names and ages.
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To define an interface, use the `interfaces` section of the config.
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**app/_graphql/schema.yml**
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```yaml
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interfaces:
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Person:
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fields:
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firstName: String!
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surname: String!
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age: Int!
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resolveType: [ 'MyProject\MyResolver', 'resolvePersonType' ]
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```
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Interfaces must define a `resolveType` resolver method to inform the interface
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which type it is applied to given a specific result. This method is non-discoverable and
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must be applied explicitly.
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```php
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public static function resolvePersonType($object): string
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{
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if ($object instanceof Actor) {
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return 'Actor';
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}
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if ($object instanceof Chef) {
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return 'Chef';
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}
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}
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```
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### Union types
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A union type is used when a field can resolve to multiple types. For example, a query
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for "Articles" could return a list containing both "Blog" and "NewsStory" types.
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To add a union type, use the `unions` section of the configuration.
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**app/_graphql/schema.yml**
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```yaml
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unions:
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Article:
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types: [ 'Blog', 'NewsStory' ]
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typeResolver: [ 'MyProject\MyResolver', 'resolveArticleUnion' ]
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```
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Like interfaces, unions need to know how to resolve their types. These methods are also
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non-discoverable and must be applied explicitly.
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```php
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public static function resolveArticleUnion(Article $object): string
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{
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if ($object->category === 'blogs')
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return 'Blog';
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}
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if ($object->category === 'news') {
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return 'NewsStory';
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}
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}
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```
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### Further reading
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[CHILDREN]
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