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.
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: A GraphQLSchema instance from GraphQL.js.
A schema must be provided.
-
graphiql: If true, presents GraphiQL when the GraphQL endpoint is
loaded in a browser. We recommend that you set graphiql to true when your
app is in development, because it's quite useful. You may or may not want it
in production.
Alternatively, instead of true 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.
-
headerEditorEnabled: An optional boolean which enables the header editor when true.
Defaults to false.
-
rootValue: A value to pass as the rootValue to the graphql()
function from GraphQL.js/src/execute.js.
-
context: A value to pass as the context to the graphql()
function from GraphQL.js/src/execute.js. If context is not provided, the
request object is passed as the context.
-
pretty: If true, 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 the
"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 default validate from graphql-js.
-
customExecuteFn: An optional function which will be used to execute
instead of default execute from graphql-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-compliant formatError function will be used.
-
customParseFn: An optional function which will be used to create a document
instead of the default parse from graphql-js.
-
formatError: is deprecated and replaced by customFormatErrorFn. 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 provided query contains multiple named
operations, this specifies which operation should be executed. If not
provided, a 400 error will be returned if the query contains multiple
named operations.
-
raw: If the graphiql option is enabled and the raw 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 query string of a URL:
/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 the query 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 field name 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`,
),
);
}
},
};
}
Disabling introspection
Disabling introspection does not reflect best practices and does not necessarily make your
application any more secure. Nevertheless, disabling introspection is possible by utilizing the
NoSchemaIntrospectionCustomRule provided by the graphql-js
package.
import { specifiedRules, NoSchemaIntrospectionCustomRule } from 'graphql';
app.use(
'/graphql',
graphqlHTTP((request) => {
return {
schema: MyGraphQLSchema,
validationRules: [...specifiedRules, NoSchemaIntrospectionCustomRule],
};
}),
);
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 { getGraphQLParams } = require('express-graphql');
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,
});
