mirror of
https://github.com/silverstripe/silverstripe-framework
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93 lines
2.3 KiB
Markdown
93 lines
2.3 KiB
Markdown
---
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title: Writing a simple plugin
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summary: In this tutorial, we add a simple plugin for string fields
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---
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# Plugins
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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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## Writing a simple plugin
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For this example, we want all `String` fields to have a `truncate` argument that will limit the length of the string
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in the response.
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Because it applies to fields, we'll want `FieldPlugin` for this.
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```php
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class Truncator implements FieldPlugin
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{
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public function getIdentifier(): string
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{
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return 'truncate';
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}
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public function apply(Field $field, Schema $schema, array $config = [])
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{
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$field->addArg('truncate', 'Int');
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}
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}
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```
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Now we've added an argument to any field that implements the `truncate` plugin. This is good, but it really
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doesn't save us a whole lot of time. The real value here is that the field will automatically apply the truncation.
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For that, we'll need to augment the resolver with some _afterware_.
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```php
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public function apply(Field $field, Schema $schema, array $config = [])
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{
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// Sanity check
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Schema::invariant(
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$field->getType() === 'String',
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'Field %s is not a string. Cannot truncate.',
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$field->getName()
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);
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$field->addArg('truncate', 'Int');
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$field->addResolverAfterware([static::class, 'truncate']);
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}
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public static function truncate(string $result, array $args): string
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{
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$limit = $args['truncate'] ?? null;
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if ($limit) {
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return substr($result, 0, $limit);
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}
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return $result;
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}
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```
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Let's register the plugin:
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```yaml
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SilverStripe\Core\Injector\Injector:
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SilverStripe\GraphQL\Schema\Registry\PluginRegistry:
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constructor:
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- 'MyProject\Plugins\Truncator'
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```
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And now we can apply it to any string field we want:
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**app/_graphql/types.yml**
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```yaml
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Country:
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name:
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type: String
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plugins:
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truncate: true
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```
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### Further reading
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[CHILDREN]
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