GraphQL HTTP Server Middleware
Create a GraphQL HTTP server with any HTTP web framework that supports connect styled middleware, including Connect itself, Express and Restify.
Installation
npm install --save express-graphql
TypeScript
This module includes a TypeScript
declaration file to enable auto complete in compatible editors and type
information for TypeScript projects. This module depends on 'graphql' and the Node.js
types, so install @types/graphql
and @types/node
:
$ npm install --save --dev @types/graphql @types/node
Simple Setup
Just mount express-graphql
as a route handler:
const express = require('express');
const graphqlHTTP = require('express-graphql');
const app = express();
app.use(
'/graphql',
graphqlHTTP({
schema: MyGraphQLSchema,
graphiql: true,
}),
);
app.listen(4000);
Setup with Restify
Use .get
or .post
(or both) rather than .use
to configure your route handler. If you want to show GraphiQL in the browser, set graphiql: true
on your .get
handler.
const restify = require('restify');
const graphqlHTTP = require('express-graphql');
const app = restify.createServer();
app.post(
'/graphql',
graphqlHTTP({
schema: MyGraphQLSchema,
graphiql: false,
}),
);
app.get(
'/graphql',
graphqlHTTP({
schema: MyGraphQLSchema,
graphiql: true,
}),
);
app.listen(4000);
Options
The graphqlHTTP
function accepts the following options:
-
schema
: AGraphQLSchema
instance fromGraphQL.js
. Aschema
must be provided. -
graphiql
: Iftrue
, presents GraphiQL when the GraphQL endpoint is loaded in a browser. We recommend that you setgraphiql
totrue
when your app is in development, because it's quite useful. You may or may not want it in production. Alternatively, instead oftrue
you can pass in an options object:-
defaultQuery
: An optional GraphQL string to use when no query is provided and no stored query exists from a previous session. If undefined is provided, GraphiQL will use its own default query.
-
-
rootValue
: A value to pass as therootValue
to thegraphql()
function fromGraphQL.js/src/execute.js
. -
context
: A value to pass as thecontext
to thegraphql()
function fromGraphQL.js/src/execute.js
. Ifcontext
is not provided, therequest
object is passed as the context. -
pretty
: Iftrue
, any JSON response will be pretty-printed. -
extensions
: An optional function for adding additional metadata to the GraphQL response as a key-value object. The result will be added to"extensions"
field in the resulting JSON. This is often a useful place to add development time metadata such as the runtime of a query or the amount of resources consumed. This may be an async function. The function is given one object as an argument:{ document, variables, operationName, result, context }
. -
validationRules
: Optional additional validation rules queries must satisfy in addition to those defined by the GraphQL spec. -
customValidateFn
: An optional function which will be used to validate instead of defaultvalidate
fromgraphql-js
. -
customExecuteFn
: An optional function which will be used to execute instead of defaultexecute
fromgraphql-js
. -
customFormatErrorFn
: An optional function which will be used to format any errors produced by fulfilling a GraphQL operation. If no function is provided, GraphQL's default spec-compliantformatError
function will be used. -
customParseFn
: An optional function which will be used to create a document instead of the defaultparse
fromgraphql-js
. -
formatError
: is deprecated and replaced bycustomFormatErrorFn
. It will be removed in version 1.0.0.
In addition to an object defining each option, options can also be provided as
a function (or async function) which returns this options object. This function
is provided the arguments (request, response, graphQLParams)
and is called
after the request has been parsed.
The graphQLParams
is provided as the object { query, variables, operationName, raw }
.
app.use(
'/graphql',
graphqlHTTP(async (request, response, graphQLParams) => ({
schema: MyGraphQLSchema,
rootValue: await someFunctionToGetRootValue(request),
graphiql: true,
})),
);
HTTP Usage
Once installed at a path, express-graphql
will accept requests with
the parameters:
-
query
: A string GraphQL document to be executed. -
variables
: The runtime values to use for any GraphQL query variables as a JSON object. -
operationName
: If the providedquery
contains multiple named operations, this specifies which operation should be executed. If not provided, a 400 error will be returned if thequery
contains multiple named operations. -
raw
: If thegraphiql
option is enabled and theraw
parameter is provided raw JSON will always be returned instead of GraphiQL even when loaded from a browser.
GraphQL will first look for each parameter in the URL's query-string:
/graphql?query=query+getUser($id:ID){user(id:$id){name}}&variables={"id":"4"}
If not found in the query-string, it will look in the POST request body.
If a previous middleware has already parsed the POST body, the request.body
value will be used. Use multer
or a similar middleware to add support
for multipart/form-data
content, which may be useful for GraphQL mutations
involving uploading files. See an example using multer.
If the POST body has not yet been parsed, express-graphql will interpret it depending on the provided Content-Type header.
-
application/json
: the POST body will be parsed as a JSON object of parameters. -
application/x-www-form-urlencoded
: this POST body will be parsed as a url-encoded string of key-value pairs. -
application/graphql
: The POST body will be parsed as GraphQL query string, which provides thequery
parameter.
Combining with Other Express Middleware
By default, the express request is passed as the GraphQL context
.
Since most express middleware operates by adding extra data to the
request object, this means you can use most express middleware just by inserting it before graphqlHTTP
is mounted. This covers scenarios such as authenticating the user, handling file uploads, or mounting GraphQL on a dynamic endpoint.
This example uses express-session
to provide GraphQL with the currently logged-in session.
const session = require('express-session');
const graphqlHTTP = require('express-graphql');
const app = express();
app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 } }));
app.use(
'/graphql',
graphqlHTTP({
schema: MySessionAwareGraphQLSchema,
graphiql: true,
}),
);
Then in your type definitions, you can access the request via the third "context" argument in your resolve
function:
new GraphQLObjectType({
name: 'MyType',
fields: {
myField: {
type: GraphQLString,
resolve(parentValue, args, request) {
// use `request.session` here
},
},
},
});
Providing Extensions
The GraphQL response allows for adding additional information in a response to
a GraphQL query via a field in the response called "extensions"
. This is added
by providing an extensions
function when using graphqlHTTP
. The function
must return a JSON-serializable Object.
When called, this is provided an argument which you can use to get information about the GraphQL request:
{ document, variables, operationName, result, context }
This example illustrates adding the amount of time consumed by running the provided query, which could perhaps be used by your development tools.
const graphqlHTTP = require('express-graphql');
const app = express();
app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 } }));
const extensions = ({
document,
variables,
operationName,
result,
context,
}) => {
return {
runTime: Date.now() - context.startTime,
};
};
app.use(
'/graphql',
graphqlHTTP(request => {
return {
schema: MyGraphQLSchema,
context: { startTime: Date.now() },
graphiql: true,
extensions,
};
}),
);
When querying this endpoint, it would include this information in the result, for example:
{
"data": { ... }
"extensions": {
"runTime": 135
}
}
Additional Validation Rules
GraphQL's validation phase checks the query to ensure that it can be successfully executed against the schema. The validationRules
option allows for additional rules to be run during this phase. Rules are applied to each node in an AST representing the query using the Visitor pattern.
A validation rule is a function which returns a visitor for one or more node Types. Below is an example of a validation preventing the specific fieldname metadata
from being queried. For more examples see the specifiedRules
in the graphql-js package.
import { GraphQLError } from 'graphql';
export function DisallowMetadataQueries(context) {
return {
Field(node) {
const fieldName = node.name.value;
if (fieldName === 'metadata') {
context.reportError(
new GraphQLError(
`Validation: Requesting the field ${fieldName} is not allowed`,
),
);
}
},
};
}
Other Exports
getGraphQLParams(request: Request): Promise<GraphQLParams>
Given an HTTP Request, this returns a Promise for the parameters relevant to running a GraphQL request. This function is used internally to handle the incoming request, you may use it directly for building other similar services.
const graphqlHTTP = require('express-graphql');
graphqlHTTP.getGraphQLParams(request).then(params => {
// do something...
});
Debugging Tips
During development, it's useful to get more information from errors, such as
stack traces. Providing a function to customFormatErrorFn
enables this:
customFormatErrorFn: error => ({
message: error.message,
locations: error.locations,
stack: error.stack ? error.stack.split('\n') : [],
path: error.path,
});