Constraints

June 25, 2021 ยท View on GitHub

This example serves as a simple tutorial on how to declare and use constraints on fields, arguments and objects.

This example depends on optional package infinityloop-dev/graphpinator-constraint-directives.

Introduction

In this example, we define a simple schema with a few constraints - custom directives that apply value constraints to fields, arguments and types. You should be familiar with our previous HelloWorld example to understand the basics.

Define our types

Here we define one Query object type with some leaf constraints and one AOrB object type with object constraint. In this specific example, we assign

  • StringConstraint to the fieldConstraint field, which specifies that returned string is at least 5 characters long,
  • IntConstraint to the arg argument on argumentConstraint field, which specifies that inputed int must be >= 10,
  • ObjectConstraint to the AOrB type, which specifies that either fieldA or fieldB contains a value.
<?php

declare(strict_types = 1);

namespace Example;

final class Query extends \Graphpinator\Typesystem\Type
{
    protected const NAME = 'Query';
    protected const DESCRIPTION = 'Graphpinator Constraints: Query type';

    public function __construct(
        private \Graphpinator\ConstraintDirectives\StringConstraintDirective $stringConstraint,
        private \Graphpinator\ConstraintDirectives\IntConstraintDirective $intConstraint,
    )
    {
        parent::__construct();
    }

    public function validateNonNullValue($rawValue) : bool
    {
        return true;
    }

    protected function getFieldDefinition() : \Graphpinator\Typesystem\Field\ResolvableFieldSet
    {
        return new \Graphpinator\Typesystem\Field\ResolvableFieldSet([
            \Graphpinator\Typesystem\Field\ResolvableField::create(
                'fieldConstraint',
                \Graphpinator\Typesystem\Container::String()->notNull(),
                function ($parent) : string {
                    return 'Hello world';
                },
            )->addDirective($this->stringConstraint, ['minLength' => 5]),
            \Graphpinator\Typesystem\Field\ResolvableField::create(
                'argumentConstraint',
                \Graphpinator\Typesystem\Container::Int()->notNull(),
                function ($parent, int $arg) : int {
                    return $arg;
                },
            )->setArguments(
                new \Graphpinator\Typesystem\Argument\ArgumentSet([
                    \Graphpinator\Typesystem\Argument\Argument::create(
                        'arg',
                        \Graphpinator\Typesystem\Container::Int()->notNull(),
                    )->addDirective($this->intConstraint, ['min' => 10]),
                ])
            ),
        ]);
    }
}

final class AOrB extends \Graphpinator\Typesystem\Type
{
    protected const NAME = 'AOrB';
    protected const DESCRIPTION = 'Graphpinator Constraints: AOrB type';

    public function __construct(
        private \Graphpinator\ConstraintDirectives\ObjectConstraintDirective $objectConstraint,
    )
    {
        parent::__construct();

        $this->addDirective($objectConstraint, ['exactlyOne' => ['fieldA', 'fieldB']]);
    }

    public function validateNonNullValue($rawValue) : bool
    {
        return \is_int($rawValue) && \in_array($rawValue, [0, 1], true);
    }

    protected function getFieldDefinition() : \Graphpinator\Typesystem\Field\ResolvableFieldSet
    {
        return new \Graphpinator\Typesystem\Field\ResolvableFieldSet([
            \Graphpinator\Typesystem\Field\ResolvableField::create(
                'fieldA',
                \Graphpinator\Typesystem\Container::Int(),
                function (?int $parent) : ?int {
                    return $parent === 1 ? 1 : null;
                },
            ),
            \Graphpinator\Typesystem\Field\ResolvableField::create(
                'fieldB',
                \Graphpinator\Typesystem\Container::Int(),
                function (int $parent) : ?int {
                    return $parent === 0 ? 1 : null;
                },
            ),
        ]);
    }
}

Make sure to select Constraint corresponding to its usage e.g.

  • StringConstraint for String fields/arguments
  • ObjectConstraint for types/interfaces/inputs

Check schema definition

Visualize our GraphQL schema in type language.

Declaration of Container, Schema and Graphpinator classes is skipped in this example. Visit our HelloWorld example for more information.

Printing the schema using infinityloop-dev/graphpinator-printer produces following schema.

schema {
  query: Query
  mutation: null
  subscription: null
}

"""
Graphpinator Constraints: AOrB type
"""
type AOrB @objectConstraint(exactlyOne: ["fieldA", "fieldB"]) {
  fieldA: Int
  fieldB: Int
}

"""
Graphpinator Constraints: Query type
"""
type Query {
  fieldConstraint: String! @stringConstraint(minLength: 5)
  argumentConstraint(
    arg: Int! @intConstraint(min: 10)
  ): Int!
}

Congratulations

This is the end of the Constraints example, thank you for reading this far.