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execute.js
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/* @flow */
/**
* Copyright (c) 2015, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*/
import { GraphQLError, locatedError } from '../error';
import find from '../jsutils/find';
import invariant from '../jsutils/invariant';
import isNullish from '../jsutils/isNullish';
import { typeFromAST } from '../utilities/typeFromAST';
import { Kind } from '../language';
import { getVariableValues, getArgumentValues } from './values';
import {
GraphQLScalarType,
GraphQLObjectType,
GraphQLEnumType,
GraphQLList,
GraphQLNonNull,
GraphQLInterfaceType,
GraphQLUnionType,
isAbstractType
} from '../type/definition';
import type {
GraphQLType,
GraphQLLeafType,
GraphQLAbstractType,
GraphQLFieldDefinition,
GraphQLFieldResolveFn,
GraphQLResolveInfo,
} from '../type/definition';
import { GraphQLSchema } from '../type/schema';
import {
SchemaMetaFieldDef,
TypeMetaFieldDef,
TypeNameMetaFieldDef
} from '../type/introspection';
import {
GraphQLIncludeDirective,
GraphQLSkipDirective
} from '../type/directives';
import type {
Directive,
Document,
OperationDefinition,
SelectionSet,
Field,
InlineFragment,
FragmentDefinition
} from '../language/ast';
/**
* Terminology
*
* "Definitions" are the generic name for top-level statements in the document.
* Examples of this include:
* 1) Operations (such as a query)
* 2) Fragments
*
* "Operations" are a generic name for requests in the document.
* Examples of this include:
* 1) query,
* 2) mutation
*
* "Selections" are the definitions that can appear legally and at
* single level of the query. These include:
* 1) field references e.g "a"
* 2) fragment "spreads" e.g. "...c"
* 3) inline fragment "spreads" e.g. "...on Type { a }"
*/
/**
* Data that must be available at all points during query execution.
*
* Namely, schema of the type system that is currently executing,
* and the fragments defined in the query document
*/
type ExecutionContext = {
schema: GraphQLSchema;
fragments: {[key: string]: FragmentDefinition};
rootValue: mixed;
contextValue: mixed;
operation: OperationDefinition;
variableValues: {[key: string]: mixed};
errors: Array<GraphQLError>;
}
/**
* The result of execution. `data` is the result of executing the
* query, `errors` is null if no errors occurred, and is a
* non-empty array if an error occurred.
*/
type ExecutionResult = {
data: ?Object;
errors?: Array<GraphQLError>;
}
/**
* Implements the "Evaluating requests" section of the GraphQL specification.
*
* Returns a Promise that will eventually be resolved and never rejected.
*
* If the arguments to this function do not result in a legal execution context,
* a GraphQLError will be thrown immediately explaining the invalid input.
*/
export function execute(
schema: GraphQLSchema,
documentAST: Document,
rootValue?: mixed,
contextValue?: mixed,
variableValues?: ?{[key: string]: mixed},
operationName?: ?string
): Promise<ExecutionResult> {
invariant(schema, 'Must provide schema');
invariant(
schema instanceof GraphQLSchema,
'Schema must be an instance of GraphQLSchema. Also ensure that there are ' +
'not multiple versions of GraphQL installed in your node_modules directory.'
);
// If a valid context cannot be created due to incorrect arguments,
// this will throw an error.
const context = buildExecutionContext(
schema,
documentAST,
rootValue,
contextValue,
variableValues,
operationName
);
// Return a Promise that will eventually resolve to the data described by
// The "Response" section of the GraphQL specification.
//
// If errors are encountered while executing a GraphQL field, only that
// field and its descendants will be omitted, and sibling fields will still
// be executed. An execution which encounters errors will still result in a
// resolved Promise.
return new Promise(resolve => {
resolve(executeOperation(context, context.operation, rootValue));
}).catch(error => {
// Errors from sub-fields of a NonNull type may propagate to the top level,
// at which point we still log the error and null the parent field, which
// in this case is the entire response.
context.errors.push(error);
return null;
}).then(data => {
if (!context.errors.length) {
return { data };
}
return { data, errors: context.errors };
});
}
/**
* Constructs a ExecutionContext object from the arguments passed to
* execute, which we will pass throughout the other execution methods.
*
* Throws a GraphQLError if a valid execution context cannot be created.
*/
function buildExecutionContext(
schema: GraphQLSchema,
documentAST: Document,
rootValue: mixed,
contextValue: mixed,
rawVariableValues: ?{[key: string]: mixed},
operationName: ?string
): ExecutionContext {
const errors: Array<GraphQLError> = [];
let operation: ?OperationDefinition;
const fragments: {[name: string]: FragmentDefinition} = Object.create(null);
documentAST.definitions.forEach(definition => {
switch (definition.kind) {
case Kind.OPERATION_DEFINITION:
if (!operationName && operation) {
throw new GraphQLError(
'Must provide operation name if query contains multiple operations.'
);
}
if (!operationName ||
definition.name && definition.name.value === operationName) {
operation = definition;
}
break;
case Kind.FRAGMENT_DEFINITION:
fragments[definition.name.value] = definition;
break;
default: throw new GraphQLError(
`GraphQL cannot execute a request containing a ${definition.kind}.`,
definition
);
}
});
if (!operation) {
if (operationName) {
throw new GraphQLError(`Unknown operation named "${operationName}".`);
} else {
throw new GraphQLError('Must provide an operation.');
}
}
const variableValues = getVariableValues(
schema,
operation.variableDefinitions || [],
rawVariableValues || {}
);
return {
schema,
fragments,
rootValue,
contextValue,
operation,
variableValues,
errors
};
}
/**
* Implements the "Evaluating operations" section of the spec.
*/
function executeOperation(
exeContext: ExecutionContext,
operation: OperationDefinition,
rootValue: mixed
): Object {
const type = getOperationRootType(exeContext.schema, operation);
const fields = collectFields(
exeContext,
type,
operation.selectionSet,
Object.create(null),
Object.create(null)
);
const path = [];
if (operation.operation === 'mutation') {
return executeFieldsSerially(exeContext, type, rootValue, path, fields);
}
return executeFields(exeContext, type, rootValue, path, fields);
}
/**
* Extracts the root type of the operation from the schema.
*/
function getOperationRootType(
schema: GraphQLSchema,
operation: OperationDefinition
): GraphQLObjectType {
switch (operation.operation) {
case 'query':
return schema.getQueryType();
case 'mutation':
const mutationType = schema.getMutationType();
if (!mutationType) {
throw new GraphQLError(
'Schema is not configured for mutations',
[ operation ]
);
}
return mutationType;
case 'subscription':
const subscriptionType = schema.getSubscriptionType();
if (!subscriptionType) {
throw new GraphQLError(
'Schema is not configured for subscriptions',
[ operation ]
);
}
return subscriptionType;
default:
throw new GraphQLError(
'Can only execute queries, mutations and subscriptions',
[ operation ]
);
}
}
/**
* Implements the "Evaluating selection sets" section of the spec
* for "write" mode.
*/
function executeFieldsSerially(
exeContext: ExecutionContext,
parentType: GraphQLObjectType,
sourceValue: mixed,
path: Array<string | number>,
fields: {[key: string]: Array<Field>}
): Promise<Object> {
return Object.keys(fields).reduce(
(prevPromise, responseName) => prevPromise.then(results => {
const fieldASTs = fields[responseName];
const fieldPath = path.concat([ responseName ]);
const result = resolveField(
exeContext,
parentType,
sourceValue,
fieldASTs,
fieldPath
);
if (result === undefined) {
return results;
}
if (isThenable(result)) {
return ((result: any): Promise).then(resolvedResult => {
results[responseName] = resolvedResult;
return results;
});
}
results[responseName] = result;
return results;
}),
Promise.resolve({})
);
}
/**
* Implements the "Evaluating selection sets" section of the spec
* for "read" mode.
*/
function executeFields(
exeContext: ExecutionContext,
parentType: GraphQLObjectType,
sourceValue: mixed,
path: Array<string | number>,
fields: {[key: string]: Array<Field>}
): Object {
let containsPromise = false;
const finalResults = Object.keys(fields).reduce(
(results, responseName) => {
const fieldASTs = fields[responseName];
const fieldPath = path.concat([ responseName ]);
const result = resolveField(
exeContext,
parentType,
sourceValue,
fieldASTs,
fieldPath
);
if (result === undefined) {
return results;
}
results[responseName] = result;
if (isThenable(result)) {
containsPromise = true;
}
return results;
},
Object.create(null)
);
// If there are no promises, we can just return the object
if (!containsPromise) {
return finalResults;
}
// Otherwise, results is a map from field name to the result
// of resolving that field, which is possibly a promise. Return
// a promise that will return this same map, but with any
// promises replaced with the values they resolved to.
return promiseForObject(finalResults);
}
/**
* Given a selectionSet, adds all of the fields in that selection to
* the passed in map of fields, and returns it at the end.
*
* CollectFields requires the "runtime type" of an object. For a field which
* returns and Interface or Union type, the "runtime type" will be the actual
* Object type returned by that field.
*/
function collectFields(
exeContext: ExecutionContext,
runtimeType: GraphQLObjectType,
selectionSet: SelectionSet,
fields: {[key: string]: Array<Field>},
visitedFragmentNames: {[key: string]: boolean}
): {[key: string]: Array<Field>} {
for (let i = 0; i < selectionSet.selections.length; i++) {
const selection = selectionSet.selections[i];
switch (selection.kind) {
case Kind.FIELD:
if (!shouldIncludeNode(exeContext, selection.directives)) {
continue;
}
const name = getFieldEntryKey(selection);
if (!fields[name]) {
fields[name] = [];
}
fields[name].push(selection);
break;
case Kind.INLINE_FRAGMENT:
if (!shouldIncludeNode(exeContext, selection.directives) ||
!doesFragmentConditionMatch(exeContext, selection, runtimeType)) {
continue;
}
collectFields(
exeContext,
runtimeType,
selection.selectionSet,
fields,
visitedFragmentNames
);
break;
case Kind.FRAGMENT_SPREAD:
const fragName = selection.name.value;
if (visitedFragmentNames[fragName] ||
!shouldIncludeNode(exeContext, selection.directives)) {
continue;
}
visitedFragmentNames[fragName] = true;
const fragment = exeContext.fragments[fragName];
if (!fragment ||
!doesFragmentConditionMatch(exeContext, fragment, runtimeType)) {
continue;
}
collectFields(
exeContext,
runtimeType,
fragment.selectionSet,
fields,
visitedFragmentNames
);
break;
}
}
return fields;
}
/**
* Determines if a field should be included based on the @include and @skip
* directives, where @skip has higher precidence than @include.
*/
function shouldIncludeNode(
exeContext: ExecutionContext,
directives: ?Array<Directive>
): boolean {
const skipAST = directives && find(
directives,
directive => directive.name.value === GraphQLSkipDirective.name
);
if (skipAST) {
const { if: skipIf } = getArgumentValues(
GraphQLSkipDirective.args,
skipAST.arguments,
exeContext.variableValues
);
if (skipIf === true) {
return false;
}
}
const includeAST = directives && find(
directives,
directive => directive.name.value === GraphQLIncludeDirective.name
);
if (includeAST) {
const { if: includeIf } = getArgumentValues(
GraphQLIncludeDirective.args,
includeAST.arguments,
exeContext.variableValues
);
if (includeIf === false) {
return false;
}
}
return true;
}
/**
* Determines if a fragment is applicable to the given type.
*/
function doesFragmentConditionMatch(
exeContext: ExecutionContext,
fragment: FragmentDefinition | InlineFragment,
type: GraphQLObjectType
): boolean {
const typeConditionAST = fragment.typeCondition;
if (!typeConditionAST) {
return true;
}
const conditionalType = typeFromAST(exeContext.schema, typeConditionAST);
if (conditionalType === type) {
return true;
}
if (isAbstractType(conditionalType)) {
const abstractType = ((conditionalType: any): GraphQLAbstractType);
return exeContext.schema.isPossibleType(abstractType, type);
}
return false;
}
/**
* This function transforms a JS object `{[key: string]: Promise<T>}` into
* a `Promise<{[key: string]: T}>`
*
* This is akin to bluebird's `Promise.props`, but implemented only using
* `Promise.all` so it will work with any implementation of ES6 promises.
*/
function promiseForObject<T>(
object: {[key: string]: Promise<T>}
): Promise<{[key: string]: T}> {
const keys = Object.keys(object);
const valuesAndPromises = keys.map(name => object[name]);
return Promise.all(valuesAndPromises).then(
values => values.reduce((resolvedObject, value, i) => {
resolvedObject[keys[i]] = value;
return resolvedObject;
}, Object.create(null))
);
}
/**
* Implements the logic to compute the key of a given field’s entry
*/
function getFieldEntryKey(node: Field): string {
return node.alias ? node.alias.value : node.name.value;
}
/**
* Resolves the field on the given source object. In particular, this
* figures out the value that the field returns by calling its resolve function,
* then calls completeValue to complete promises, serialize scalars, or execute
* the sub-selection-set for objects.
*/
function resolveField(
exeContext: ExecutionContext,
parentType: GraphQLObjectType,
source: mixed,
fieldASTs: Array<Field>,
path: Array<string | number>
): mixed {
const fieldAST = fieldASTs[0];
const fieldName = fieldAST.name.value;
const fieldDef = getFieldDef(exeContext.schema, parentType, fieldName);
if (!fieldDef) {
return;
}
const returnType = fieldDef.type;
const resolveFn = fieldDef.resolve || defaultResolveFn;
// Build a JS object of arguments from the field.arguments AST, using the
// variables scope to fulfill any variable references.
// TODO: find a way to memoize, in case this field is within a List type.
const args = getArgumentValues(
fieldDef.args,
fieldAST.arguments,
exeContext.variableValues
);
// The resolve function's optional third argument is a context value that
// is provided to every resolve function within an execution. It is commonly
// used to represent an authenticated user, or request-specific caches.
const context = exeContext.contextValue;
// The resolve function's optional fourth argument is a collection of
// information about the current execution state.
const info: GraphQLResolveInfo = {
fieldName,
fieldASTs,
returnType,
parentType,
path,
schema: exeContext.schema,
fragments: exeContext.fragments,
rootValue: exeContext.rootValue,
operation: exeContext.operation,
variableValues: exeContext.variableValues,
};
// Get the resolve function, regardless of if its result is normal
// or abrupt (error).
const result = resolveOrError(resolveFn, source, args, context, info);
return completeValueCatchingError(
exeContext,
returnType,
fieldASTs,
info,
path,
result
);
}
// Isolates the "ReturnOrAbrupt" behavior to not de-opt the `resolveField`
// function. Returns the result of resolveFn or the abrupt-return Error object.
function resolveOrError(
resolveFn: GraphQLFieldResolveFn,
source: mixed,
args: { [key: string]: mixed },
context: mixed,
info: GraphQLResolveInfo
): Error | mixed {
try {
return resolveFn(source, args, context, info);
} catch (error) {
// Sometimes a non-error is thrown, wrap it as an Error for a
// consistent interface.
return error instanceof Error ? error : new Error(error);
}
}
// This is a small wrapper around completeValue which detects and logs errors
// in the execution context.
function completeValueCatchingError(
exeContext: ExecutionContext,
returnType: GraphQLType,
fieldASTs: Array<Field>,
info: GraphQLResolveInfo,
path: Array<string | number>,
result: mixed
): mixed {
// If the field type is non-nullable, then it is resolved without any
// protection from errors.
if (returnType instanceof GraphQLNonNull) {
return completeValue(
exeContext,
returnType,
fieldASTs,
info,
path,
result
);
}
// Otherwise, error protection is applied, logging the error and resolving
// a null value for this field if one is encountered.
try {
const completed = completeValue(
exeContext,
returnType,
fieldASTs,
info,
path,
result
);
if (isThenable(completed)) {
// If `completeValue` returned a rejected promise, log the rejection
// error and resolve to null.
// Note: we don't rely on a `catch` method, but we do expect "thenable"
// to take a second callback for the error case.
return ((completed: any): Promise).then(undefined, error => {
exeContext.errors.push(error);
return Promise.resolve(null);
});
}
return completed;
} catch (error) {
// If `completeValue` returned abruptly (threw an error), log the error
// and return null.
exeContext.errors.push(error);
return null;
}
}
/**
* Implements the instructions for completeValue as defined in the
* "Field entries" section of the spec.
*
* If the field type is Non-Null, then this recursively completes the value
* for the inner type. It throws a field error if that completion returns null,
* as per the "Nullability" section of the spec.
*
* If the field type is a List, then this recursively completes the value
* for the inner type on each item in the list.
*
* If the field type is a Scalar or Enum, ensures the completed value is a legal
* value of the type by calling the `serialize` method of GraphQL type
* definition.
*
* If the field is an abstract type, determine the runtime type of the value
* and then complete based on that type
*
* Otherwise, the field type expects a sub-selection set, and will complete the
* value by evaluating all sub-selections.
*/
function completeValue(
exeContext: ExecutionContext,
returnType: GraphQLType,
fieldASTs: Array<Field>,
info: GraphQLResolveInfo,
path: Array<string | number>,
result: mixed
): mixed {
// If result is a Promise, apply-lift over completeValue.
if (isThenable(result)) {
return ((result: any): Promise).then(
// Once resolved to a value, complete that value.
resolved => completeValue(
exeContext,
returnType,
fieldASTs,
info,
path,
resolved
),
// If rejected, create a located error, and continue to reject.
error => Promise.reject(locatedError(error, fieldASTs, path))
);
}
// If result is an Error, throw a located error.
if (result instanceof Error) {
throw locatedError(result, fieldASTs, path);
}
// If field type is NonNull, complete for inner type, and throw field error
// if result is null.
if (returnType instanceof GraphQLNonNull) {
const completed = completeValue(
exeContext,
returnType.ofType,
fieldASTs,
info,
path,
result
);
if (completed === null) {
throw new GraphQLError(
`Cannot return null for non-nullable field ${
info.parentType}.${info.fieldName}.`,
fieldASTs
);
}
return completed;
}
// If result value is null-ish (null, undefined, or NaN) then return null.
if (isNullish(result)) {
return null;
}
// If field type is List, complete each item in the list with the inner type
if (returnType instanceof GraphQLList) {
return completeListValue(
exeContext,
returnType,
fieldASTs,
info,
path,
result
);
}
// If field type is a leaf type, Scalar or Enum, serialize to a valid value,
// returning null if serialization is not possible.
if (returnType instanceof GraphQLScalarType ||
returnType instanceof GraphQLEnumType) {
return completeLeafValue(returnType, result);
}
// If field type is an abstract type, Interface or Union, determine the
// runtime Object type and complete for that type.
if (returnType instanceof GraphQLInterfaceType ||
returnType instanceof GraphQLUnionType) {
return completeAbstractValue(
exeContext,
returnType,
fieldASTs,
info,
path,
result
);
}
// If field type is Object, execute and complete all sub-selections.
if (returnType instanceof GraphQLObjectType) {
return completeObjectValue(
exeContext,
returnType,
fieldASTs,
info,
path,
result
);
}
// Not reachable. All possible output types have been considered.
invariant(
false,
`Cannot complete value of unexpected type "${returnType}".`
);
}
/**
* Complete a list value by completing each item in the list with the
* inner type
*/
function completeListValue(
exeContext: ExecutionContext,
returnType: GraphQLList,
fieldASTs: Array<Field>,
info: GraphQLResolveInfo,
path: Array<string | number>,
result: mixed
): mixed {
invariant(
Array.isArray(result),
`User Error: expected iterable, but did not find one for field ${
info.parentType}.${info.fieldName}.`
);
// This is specified as a simple map, however we're optimizing the path
// where the list contains no Promises by avoiding creating another Promise.
const itemType = returnType.ofType;
let containsPromise = false;
const completedResults = result.map((item, index) => {
// No need to modify the info object containing the path,
// since from here on it is not ever accessed by resolver functions.
const fieldPath = path.concat([ index ]);
const completedItem = completeValueCatchingError(
exeContext,
itemType,
fieldASTs,
info,
fieldPath,
item
);
if (!containsPromise && isThenable(completedItem)) {
containsPromise = true;
}
return completedItem;
});
return containsPromise ? Promise.all(completedResults) : completedResults;
}
/**
* Complete a Scalar or Enum by serializing to a valid value, returning
* null if serialization is not possible.
*/
function completeLeafValue(
returnType: GraphQLLeafType,
result: mixed
): mixed {
invariant(returnType.serialize, 'Missing serialize method on type');
const serializedResult = returnType.serialize(result);
return isNullish(serializedResult) ? null : serializedResult;
}
/**
* Complete a value of an abstract type by determining the runtime object type
* of that value, then complete the value for that type.
*/
function completeAbstractValue(
exeContext: ExecutionContext,
returnType: GraphQLAbstractType,
fieldASTs: Array<Field>,
info: GraphQLResolveInfo,
path: Array<string | number>,
result: mixed
): mixed {
const runtimeType = returnType.resolveType ?
returnType.resolveType(result, exeContext.contextValue, info) :
defaultResolveTypeFn(result, exeContext.contextValue, info, returnType);
if (!(runtimeType instanceof GraphQLObjectType)) {
throw new GraphQLError(
`Abstract type ${returnType} must resolve to an Object type at runtime ` +
`for field ${info.parentType}.${info.fieldName} with value "${result}",` +
`received "${runtimeType}".`,
fieldASTs
);
}
if (!exeContext.schema.isPossibleType(returnType, runtimeType)) {
throw new GraphQLError(
`Runtime Object type "${runtimeType}" is not a possible type ` +
`for "${returnType}".`,
fieldASTs
);
}
return completeObjectValue(
exeContext,
runtimeType,
fieldASTs,
info,
path,
result
);
}
/**
* Complete an Object value by executing all sub-selections.
*/
function completeObjectValue(
exeContext: ExecutionContext,
returnType: GraphQLObjectType,
fieldASTs: Array<Field>,
info: GraphQLResolveInfo,
path: Array<string | number>,
result: mixed
): mixed {
// If there is an isTypeOf predicate function, call it with the
// current result. If isTypeOf returns false, then raise an error rather
// than continuing execution.
if (returnType.isTypeOf &&
!returnType.isTypeOf(result, exeContext.contextValue, info)) {
throw new GraphQLError(
`Expected value of type "${returnType}" but got: ${result}.`,
fieldASTs
);
}
// Collect sub-fields to execute to complete this value.
let subFieldASTs = Object.create(null);
const visitedFragmentNames = Object.create(null);
for (let i = 0; i < fieldASTs.length; i++) {
const selectionSet = fieldASTs[i].selectionSet;
if (selectionSet) {
subFieldASTs = collectFields(
exeContext,
returnType,
selectionSet,
subFieldASTs,
visitedFragmentNames
);
}
}
return executeFields(exeContext, returnType, result, path, subFieldASTs);
}
/**
* If a resolveType function is not given, then a default resolve behavior is
* used which tests each possible type for the abstract type by calling
* isTypeOf for the object being coerced, returning the first type that matches.
*/
function defaultResolveTypeFn(
value: mixed,
context: mixed,
info: GraphQLResolveInfo,
abstractType: GraphQLAbstractType
): ?GraphQLObjectType {
const possibleTypes = info.schema.getPossibleTypes(abstractType);
for (let i = 0; i < possibleTypes.length; i++) {
const type = possibleTypes[i];
if (type.isTypeOf && type.isTypeOf(value, context, info)) {
return type;
}
}
}
/**
* If a resolve function is not given, then a default resolve behavior is used
* which takes the property of the source object of the same name as the field
* and returns it as the result, or if it's a function, returns the result
* of calling that function.
*/
function defaultResolveFn(source: any, args, context, { fieldName }) {
// ensure source is a value for which property access is acceptable.
if (typeof source === 'object' || typeof source === 'function') {
const property = source[fieldName];
return typeof property === 'function' ? source[fieldName]() : property;
}
}
/**
* Checks to see if this object acts like a Promise, i.e. has a "then"
* function.
*/
function isThenable(value: mixed): boolean {
return typeof value === 'object' &&
value !== null &&
typeof value.then === 'function';
}
/**
* This method looks up the field on the given type defintion.
* It has special casing for the two introspection fields, __schema
* and __typename. __typename is special because it can always be
* queried as a field, even in situations where no other fields
* are allowed, like on a Union. __schema could get automatically
* added to the query type, but that would require mutating type
* definitions, which would cause issues.
*/
function getFieldDef(
schema: GraphQLSchema,
parentType: GraphQLObjectType,
fieldName: string
): ?GraphQLFieldDefinition {
if (fieldName === SchemaMetaFieldDef.name &&
schema.getQueryType() === parentType) {
return SchemaMetaFieldDef;
} else if (fieldName === TypeMetaFieldDef.name &&
schema.getQueryType() === parentType) {
return TypeMetaFieldDef;
} else if (fieldName === TypeNameMetaFieldDef.name) {
return TypeNameMetaFieldDef;