README.md

GraphQL Query Rewriter

Seamlessly turn breaking GraphQL schema changes into non-breaking changes by rewriting queries in middleware.

Full API docs are available at https://ef-eng.github.io/graphql-query-rewriter

The Problem

GraphQL is great at enforcing a strict schema for APIs, but its lack of versioning makes it extremely difficult to make changes to GraphQL schemas without breaking existing clients. For example, take the following query:

query getUserById($id: String!) {
  userById(id: $id) {
    ...
  }
}

Oh no! We should have used ID! as the type for userById(id) instead of String!, but it's already in production! Now if we change our schema to use ID! instead of String! then our old clients will start getting the error Variable "$id" of type "String!" used in position expecting type "ID!". Currently your only options are to continue using the incorrect String! type forever (eeew), or make a new query with a new name, like userByIdNew(id: ID!) (gross)!

Wouldn't it be great if you could change the schema to use ID!, but just silently replace String! in old queries with ID! in your middleware so the old queries will continue to work just like they had been?

Rewrite it!

GraphQL Query Rewriter provides a way to rewrite deprecated queries in middleware so they'll conform to your new schema without needing to sully your API with awkwardly renamed and deprecated fields like doTheThingNew or doTheThingV3.

In the above example, we can set up a rewrite rule so that userById(id: String!) will be seamlessly rewritten to userById(id: ID!) using the following middleware (assuming express-graphql):

import { FieldArgTypeRewriter } from 'graphql-query-rewriter';
import { graphqlRewriterMiddleware } from 'express-graphql-query-rewriter';

const app = express();

// set up graphqlRewriterMiddleware right before graphQL gets processed
// to rewrite deprecated queries so they seamlessly work with your new schema
app.use('/graphql', graphqlRewriterMiddleware({
  rewriters: [
    new FieldArgTypeRewriter({
      fieldName: 'userById',
      argName: 'id',
      oldType: 'String!',
      newType: 'ID!'
    }),
  ]
}));

app.use('/graphql', graphqlHTTP( ... ));

...

Now, when old clients send the following query:

query getUserById($id: String!) {
  userById(id: $id) {
    ...
  }
}

It will be rewritten before it gets processed to:

query getUserById($id: ID!) {
  userById(id: $id) {
    ...
  }
}

Now your schema is clean and up to date, and deprecated clients keep working! GraphQL Schema Rewriter can rewrite much more complex queries than just changing a single input type as well.

Installation

Installation requires the base package graphql-query-rewriter and a middleware adapter for the web framework you use. Currently only graphql-express is supported, but apollo-server and more will be added soon!

# for express-graphql
npm install graphql-query-rewriter express-graphql-query-rewriter

Usage

First you need to set up an appropriate middleware for your server. Currently, only express-graphql is supported, so we'll be using the express-graphql-query-rewriter middleware. This middleware goes directy before your graphql handler in express:

import { graphqlRewriterMiddleware } from 'express-graphql-query-rewriter';

...
// graphqlRewriterMiddleware should go directly before the graphQL handler
app.use('/graphql',  graphqlRewriterMiddleware({
  rewriters: [ /* place rewriters here */]
})

app.use('/graphql', graphqlHTTP( ... ));
...

FieldArgTypeRewriter

FieldArgTypeRewriter rewrites the type of an argument to a graphQL query or mutation. For example, to change from Int to Int! in a mutation called doTheThing(arg1: Int) you could add the following:

import { FieldArgTypeRewriter } from 'graphql-query-rewriter';

// add this to the rewriters array in graphqlRewriterMiddleware(...)
const rewriter = new FieldArgTypeRewriter({
  fieldName: 'doTheThing',
  argName: 'arg1',
  oldType: 'Int',
  newType: 'Int!'
})

Sometimes, you'll need to do some preprocessing on the variables submitted to the rewritten argument to make them into the type needed by the new schema. You can do this by passing in a coerceVariable function which returns a new value of the variable. For example, the following changes the value of arg1 from Int! to String!, and also changes the value of arg1 to a string as well:

import { FieldArgTypeRewriter } from 'graphql-query-rewriter';

// add this to the rewriters array in graphqlRewriterMiddleware(...)
const rewriter = new FieldArgTypeRewriter({
  fieldName: 'doTheThing',
  argName: 'arg1',
  oldType: 'Int!',
  newType: 'String!'
  coerceVariable: (val) => `${val}`,
})

FieldArgNameRewriter

FieldArgNameRewriter rewrites the name of an argument to a graphQL query or mutation. For example, to change an argument name from userID to userId in a mutation called createUser(userID: ID!) you could add the following:

import { FieldArgNameRewriter } from 'graphql-query-rewriter';

// add this to the rewriters array in graphqlRewriterMiddleware(...)
const rewriter = new FieldArgNameRewriter({
  fieldName: 'createUser',
  oldArgName: 'userID',
  newArgName: 'userId'
})

FieldArgsToInputTypeRewriter

FieldArgsToInputTypeRewriter can be used to move mutation parameters into a single input object, by default named input. It's a best-practice to use a single input type for mutations in GraphQL, and it's required by the Relay GraphQL Spec. For example, to migrate the mutation createUser(username: String!, password: String!) to a mutation with a proper input type like:

mutation createUser(input: CreateUserInput!) { ... }

type CreateUserInput {
  username: String!
  password: String!
}

we can make this change with the following rewriter:

import { FieldArgsToInputTypeRewriter } from 'graphql-query-rewriter';

// add this to the rewriters array in graphqlRewriterMiddleware(...)
const rewriter = new FieldArgsToInputTypeRewriter({
  fieldName: 'createUser',
  argNames: ['username', 'password'],
  inputArgName: 'input' // inputArgName can be left out to use 'input' by default
})

For example, This would rewrite the following mutation:

mutation createUser($username: String!, $password: String!) {
  createUser(username: $username, password: $password) {
    ...
  }
}

and turn it into:

mutation createUser($username: String!, $password: String!) {
  createUser(input: { username: $username, password: $password }) {
    ...
  }
}

NestFieldOutputsRewriter

NestFieldOutputsRewriter can be used to move mutation outputs into a nested payload object. It's a best-practice for each mutation in GraphQL to have its own output type, and it's required by the Relay GraphQL Spec. For example, to migrate the mutation createUser(input: CreateUserInput!): User! to a mutation with a proper output payload type like:

mutation createUser(input: CreateUserInput!) CreateUserPayload

type User {
  id
  username
}

type CreateUserPayload {
  user: User!
}

we can make this change with the following rewriter:

import { NestFieldOutputsRewriter } from 'graphql-query-rewriter';

// add this to the rewriters array in graphqlRewriterMiddleware(...)
const rewriter = new NestFieldOutputsRewriter({
  fieldName: 'createUser',
  newOutputName: 'user',
  outputsToNest: ['id', 'username']
})

For example, This would rewrite the following mutation:

mutation createUser(input: CreateUserInput!) {
  createUser(input: $input) {
    id
    username
  }
}

and turn it into:

mutation createUser(input: CreateUserInput!) {
  createUser(input: $input) {
    user {
      id
      username
    }
  }
}

Current Limitations

Currently GraphQL Query Rewriter can only work with a single operation per query, and cannot properly handle aliased fields. These limitations should hopefully be fixed soon. Contributions are welcome!

License

GraphQL Query Rewriter is released under a MIT License.

Contributing

Contributions are welcome! These steps will guide you through contributing to this project:

• Fork the repo

• Clone it and install dependencies

  git clone https://github.com/ef-eng/graphql-query-rewriter yarn install

Make and commit your changes. Make sure the commands yarn run build and yarn run test:prod are working.

Finally send a GitHub Pull Request with a clear list of what you've done. Make sure all of your commits are atomic (one feature per commit). Please add tests for any features that you add or change.