graphql-php/docs/executing-queries.md

Overview

Query execution is a complex process involving multiple steps, including query parsing, validating and finally executing against your schema.

graphql-php provides convenient facade for this process in class GraphQL\GraphQL:

use GraphQL\GraphQL;

$result = GraphQL::executeQuery(
    $schema, 
    $queryString, 
    $rootValue = null, 
    $contextValue = null, 
    $variableValues = null, 
    $operationName = null,
    $fieldResolver = null,
    $validationRules = null,
    $promiseAdapter = null
);

It returns an instance of GraphQL\Executor\ExecutionResult which can be easily converted to array:

$serializableResult = $result->toArray();

Returned array contains data and errors keys, as described by GraphQL spec. This array is suitable for further serialization (e.g. using json_encode). See also section on error handling and formatting.

Description of method arguments:

Argument	Type	Notes
schema	GraphQL\Type\Schema	Required. Instance of your application Schema
queryString	string or GraphQL\Language\AST\DocumentNode	Required. Actual GraphQL query string to be parsed, validated and executed. If you parse query elsewhere before executing - pass corresponding ast document here to avoid new parsing.
rootValue	mixed	Any value that represents a root of your data graph. It is passed as 1st argument to field resolvers of Query type. Can be omitted or set to null if actual root values are fetched by Query type itself.
contextValue	mixed	Any value that holds information shared between all field resolvers. Most often they use it to pass currently logged in user, locale details, etc. It will be available as 3rd argument in all field resolvers. (see section on Field Definitions for reference) graphql-php never modifies this value and passes it as is to all underlying resolvers.
variableValues	array	Map of variable values passed along with query string. See section on query variables on official GraphQL website
operationName	string	Allows the caller to specify which operation in queryString will be run, in cases where queryString contains multiple top-level operations.
fieldResolver	callable	A resolver function to use when one is not provided by the schema. If not provided, the default field resolver is used.
validationRules	array	A set of rules for query validation step. Default value is all available rules. Empty array would allow to skip query validation (may be convenient for persisted queries which are validated before persisting and assumed valid during execution)
promiseAdapter	GraphQL\Executir\Promise\PromiseAdapter	Adapter for async-enabled PHP platforms like ReactPHP (read about async platforms integration)

Execution Result

namespace GraphQL\Executor;

class ExecutionResult 
{
    /**
     * @var array
     */
    public $data;

    /**
     * @var GraphQL\Error\Error[]
     */
    public $errors;

    /**
     *
     */
    public setErrorsHandler(callable $errorsHandler);
    
    public setErrorFormatter(callable $errorsHandler);
}

Parsing

Following reading describes implementation details of query execution process. It may clarify some internals of GraphQL but is not required to use it. Feel free to skip to next section on Error Handling for essentials.

TODOC

Validating

TODOC

Executing

TODOC

Errors explained

There are 3 types of errors in GraphQL:

• Syntax: query has invalid syntax and could not be parsed;
• Validation: query is incompatible with type system (e.g. unknown field is requested);
• Execution: occurs when some field resolver throws (or returns unexpected value).

Obviously when Syntax or Validation error is detected - process is interrupted and query is not executed.

GraphQL is forgiving to Execution errors which occur in resolvers of nullable fields. If such field throws or returns unexpected value the value of the field in response will be simply replaced with null and error entry will be registered.

If exception is thrown in non-null field - error bubbles up to first nullable field. This nullable field is
replaced with null and error entry is added to response. If all fields up to the root are non-null - data entry will be removed from response and only errors key will be presented.