Versioning a GraphQL API

Versioning is an important aspect of API design, allowing developers to introduce changes without breaking existing clients. Unlike REST APIs, which often use URL paths to indicate versioning (e.g., /v1/users), GraphQL APIs typically handle versioning differently due to their flexible nature. Below are some strategies for versioning a GraphQL API, along with explanations and sample code.

1. Schema Versioning

One common approach to versioning a GraphQL API is to maintain multiple versions of the schema. This allows clients to specify which version of the API they want to use. You can achieve this by creating separate schemas for each version and routing requests accordingly.

Example:

Suppose you have two versions of a user schema: UserV1 and UserV2. You can define them as follows:

Sample Code for Schema Versioning:

const { ApolloServer, gql } = require('apollo-server');

// Define UserV1 schema
const typeDefsV1 = gql`
    type User {
        id: ID!
        name: String!
    }

    type Query {
        users: [User ]
    }
`;

// Define UserV2 schema
const typeDefsV2 = gql`
    type User {
        id: ID!
        name: String!
        email: String!
    }

    type Query {
        users: [User ]
    }
`;

// Create Apollo Server instances for each version
const serverV1 = new ApolloServer({ typeDefs: typeDefsV1, resolvers: {} });
const serverV2 = new ApolloServer({ typeDefs: typeDefsV2, resolvers: {} });

// Start the servers
serverV1.listen({ port: 4001 }).then(({ url }) => {
    console.log(`🚀 Server V1 ready at ${url}`);
});
serverV2.listen({ port: 4002 }).then(({ url }) => {
    console.log(`🚀 Server V2 ready at ${url}`);
});

2. Field Deprecation

Another approach to versioning is to deprecate fields in the schema rather than creating entirely new versions. This allows you to introduce new fields while still supporting existing ones. Clients can be informed about deprecated fields through the schema documentation.

Example:

If you want to add an email field to the User type while keeping the existing structure, you can mark the old field as deprecated.

Sample Code for Field Deprecation:

const typeDefs = gql`
    type User {
        id: ID!
        name: String!
        email: String @deprecated(reason: "Use 'newEmail' instead.")
        newEmail: String!
    }

    type Query {
        users: [User ]
    }
`;

3. Query Parameters for Versioning

You can also use query parameters to specify the version of the API that clients want to use. This approach allows you to maintain a single endpoint while providing different responses based on the requested version.

Example:

Clients can specify the version in the query string, such as ?version=1 or ?version=2.

Sample Code for Query Parameter Versioning:

const { ApolloServer, gql } = require('apollo-server');

// Define a single schema with version handling
const typeDefs = gql`
    type User {
        id: ID!
        name: String!
        email: String
    }

    type Query {
        users(version: Int): [User ]
    }
`;

// Define resolvers with version handling
const resolvers = {
    Query: {
        users: (parent, { version }) => {
            if (version === 1) {
                return [{ id: "1", name: "Alice" }];
            } else {
                return [{ id: "1", name: "Alice", email: "alice@example.com" }];
            }
        },
    },
};

// Create Apollo Server instance
const server = new ApolloServer({ typeDefs, resolvers });

// Start the server
server.listen().then(({ url }) => {
    console.log(`🚀 Server ready at ${url}`);
});

4. Subscriptions for Real-time Updates

If your API supports subscriptions, you can version those as well. This allows clients to subscribe to specific events based on the version they are using.

Example:

You can define different subscription types for each version, allowing clients to subscribe to updates relevant to their version.

Sample Code for Subscription Versioning:

const typeDefs = gql`
    type User {
        id: ID!
        name: String!
        email: String
    }

    type Query {
        users: [User  ]
    }

    type Subscription {
        userUpdated(version: Int): User
    }
`;

// Define resolvers for subscriptions
const resolvers = {
    Subscription: {
        userUpdated: {
            subscribe: (parent, { version }) => {
                // Logic to handle subscriptions based on version
                return pubsub.asyncIterator(`USER_UPDATED_${version}`);
            },
        },
    },
};

// Create Apollo Server instance
const server = new ApolloServer({ typeDefs, resolvers });

// Start the server
server.listen().then(({ url }) => {
    console.log(`🚀 Server ready at ${url}`);
});

Conclusion

Versioning a GraphQL API can be approached in several ways, including schema versioning, field deprecation, query parameters, and subscription versioning. Each method has its advantages and trade-offs, and the choice depends on the specific needs of your application and its clients. By implementing a thoughtful versioning strategy, you can ensure that your GraphQL API remains flexible and maintainable as it evolves over time.