Interfaces

An Interface is an abstract type that includes a certain set of fields that a type must include to implement the interface. An Interface can never be returned directly but must be implemented by ‘child types’.

php-graphql represents interfaces as instances of the class GraphQLInterface, which accepts several parameters in the constructor for configuring the interface.

use GraphQL\Types\GraphQLInterface;
use GraphQL\Fields\GraphQLTypeField;
use GraphQL\Types\GraphQLNonNull;
use GraphQL\Types\GraphQLString;
use GraphQL\Types\GraphQLList;

$Character = new GraphQLInterface("Character", "A character in the Star Wars Trilogy.", function () use (&$Character, &$Episode) {
    return [
        new GraphQLTypeField("id", new GraphQLNonNull(new GraphQLString()), "The id of the character."),
        new GraphQLTypeField("name", new GraphQLString(), "The name of the character."),
        new GraphQLTypeField("friends", new GraphQLList($Character), "The friends of the character, or an empty list if they have none."),
        new GraphQLTypeField("appearsIn", new GraphQLList($Episode), "Which movies they appear in."),
    ];
}, function ($character) {
    if ($character["type"] === "human") {
        return "Human";
    }
    return "Droid";
});

GraphQLInterface Constructor

Parameters used for the GraphQLInterface constructors are (in the following order):

Parameter	Type	Description	Required
type	`string`	Name of the new interface. Used for introspection.	☑️
description	`string`	Description of the new interface. Used for introspection.	☑️
fields	`\Closure`	Function that returns an array of `GraphQLTypeField`. Each field must be implemented in the type that implements this interface. Is called as soon the fields are needed. Used during validation and execution.	☑️
resolveTypeFn	`\Closure`	Function that decides to which implementing object type a data object belongs to. If not passed, the default resolver is used. Used during validation and execution.	️

Implementing Interfaces

Interfaces can be implemented by a GraphQLObjectType, when passing the interface (reference) to the GraphQLObjectType constructor (see parameters of GraphQLObjectType constructor in the according section).