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title	summary
Writing a simple plugin	In this tutorial, we add a simple plugin for string fields

Plugins

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Writing a simple plugin

For this example, we want all String fields to have a truncate argument that will limit the length of the string in the response.

Because it applies to fields, we'll want FieldPlugin for this.

class Truncator implements FieldPlugin
{
    public function getIdentifier(): string
    {
        return 'truncate';
    }

    public function apply(Field $field, Schema $schema, array $config = [])
    {
        $field->addArg('truncate', 'Int');
    }
}

Now we've added an argument to any field that implements the truncate plugin. This is good, but it really doesn't save us a whole lot of time. The real value here is that the field will automatically apply the truncation.

For that, we'll need to augment the resolver with some afterware.

public function apply(Field $field, Schema $schema, array $config = [])
{
    // Sanity check
    Schema::invariant(
        $field->getType() === 'String',
        'Field %s is not a string. Cannot truncate.',
        $field->getName()
    );

    $field->addArg('truncate', 'Int');
    $field->addResolverAfterware([static::class, 'truncate']);
}

public static function truncate(string $result, array $args): string
{
    $limit = $args['truncate'] ?? null;
    if ($limit) {
        return substr($result, 0, $limit);
    }

    return $result;
}

Let's register the plugin:

SilverStripe\Core\Injector\Injector:
  SilverStripe\GraphQL\Schema\Registry\PluginRegistry:
    constructor:
      truncate: '%$MyProject\Plugins\Truncator'

And now we can apply it to any string field we want:

app/_graphql/types.yml

Country:
  name:
    type: String
    plugins:
      truncate: true

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Plugins

Writing a simple plugin

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