Migrating from REST to GraphQL

Differences in API logic

Migrating from REST to GraphQL represents a significant shift in API logic. The differences between REST as a style and GraphQL as a specification make it difficult—and often undesirable—to replace REST API calls with GraphQL API queries on a one to one basis. We've included specific examples of migration below.

To migrate a GitHub App from the REST API v3 to the GraphQL API v4:

  • Review the GraphQL spec
  • Review GitHub's GraphQL schema
  • Consider how any existing GitHub App you have currently interacts with the GitHub REST API v3

Examples

Significant advantages of GraphQL include:

Getting the data you need and nothing more

A single REST API v3 call retrieves a list of your organization's members:

curl -v https://api.github.com/orgs/:org/members

The REST payload contains excessive data if your goal is to retrieve only member names and links to avatars. However, a GraphQL query returns only what you specify:

query {
    organization(login:"github") {
    members(first: 100) {
      edges {
        node {
          name
          avatarUrl
        }
      }
    }
  }
}

Consider another example: retrieving a list of pull requests and checking if each one is mergeable. A call to the REST API v3 retrieves a list of pull requests and their summary representations:

curl -v https://api.github.com/repos/:owner/:repo/pulls

Determining if a pull request is mergeable requires retrieving each pull request individually for its detailed representation (a large payload) and checking whether its mergeable attribute is true or false:

curl -v https://api.github.com/repos/:owner/:repo/pulls/:number

With GraphQL, you could retrieve only the number and mergeable attributes for each pull request:

query {
    repository(owner:"octocat", name:"Hello-World") {
    pullRequests(last: 10) {
      edges {
        node {
          number
          mergeable
        }
      }
    }
  }
}

Nesting

Querying with nested fields lets you replace multiple REST calls with fewer GraphQL queries. For example, retrieving a pull request along with its commits, non-review comments, and reviews using the REST API v3 requires four separate calls:

curl -v https://api.github.com/repos/:owner/:repo/pulls/:number
curl -v https://api.github.com/repos/:owner/:repo/pulls/:number/commits
curl -v https://api.github.com/repos/:owner/:repo/issues/:number/comments
curl -v https://api.github.com/repos/:owner/:repo/pulls/:number/reviews

Using the GraphQL API v4, you can retrieve the data with a single query using nested fields:

{
  repository(owner: "octocat", name: "Hello-World") {
    pullRequest(number: 1) {
      commits(first: 10) {
        edges {
          node {
            commit {
              oid
              message
            }
          }
        }
      }
      comments(first: 10) {
        edges {
          node {
            body
            author {
              login
            }
          }
        }
      }
      reviews(first: 10) {
        edges {
          node {
            state
          }
        }
      }
    }
  }
}

You can also extend the power of this query by substituting a variable for the pull request number.

Strong typing

GraphQL schemas are strongly typed, making data handling safer.

Consider an example of adding a comment to an issue or pull request using a GraphQL mutation, and mistakenly specifying an integer rather than a string for the value of clientMutationId:

mutation {
  addComment(input:{clientMutationId: 1234, subjectId: "MDA6SXNzdWUyMjcyMDA2MTT=", body: "Looks good to me!"}) {
    clientMutationId
    commentEdge {
      node {
        body
        repository {
          id
          name
          nameWithOwner
        }
        issue {
          number
        }
      }
    }
  }
}

Executing this query returns errors specifying the expected types for the operation:

{
  "data": null,
  "errors": [
    {
      "message": "Argument 'input' on Field 'addComment' has an invalid value. Expected type 'AddCommentInput!'.",
      "locations": [
        {
          "line": 3,
          "column": 3
        }
      ]
    },
    {
      "message": "Argument 'clientMutationId' on InputObject 'AddCommentInput' has an invalid value. Expected type 'String'.",
      "locations": [
        {
          "line": 3,
          "column": 20
        }
      ]
    }
  ]
}

Wrapping 1234 in quotes transforms the value from an integer into a string, the expected type:

mutation {
  addComment(input:{clientMutationId: "1234", subjectId: "MDA6SXNzdWUyMjcyMDA2MTT=", body: "Looks good to me!"}) {
    clientMutationId
    commentEdge {
      node {
        body
        repository {
          id
          name
          nameWithOwner
        }
        issue {
          number
        }
      }
    }
  }
}