Migrating from REST to GraphQL

Differences in API logic

GitHub provides two APIs: a REST API and a GraphQL API. For more information about GitHub's APIs, see "About GitHub's APIs."

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 your code from the REST API to the GraphQL API:

• Review the GraphQL spec
• Review GitHub's GraphQL schema
• Consider how any existing code you have currently interacts with the GitHub REST API
• Use Global Node IDs to reference objects between API versions

Significant advantages of GraphQL include:

• Getting the data you need and nothing more
• Nested fields
• Strong typing

Here are examples of each.

Example: Getting the data you need and nothing more

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

curl -v http(s)://HOSTNAME/api/v3/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") { membersWithRole(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 retrieves a list of pull requests and their summary representations:

curl -v http(s)://HOSTNAME/api/v3/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 http(s)://HOSTNAME/api/v3/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 } } } } } 

Example: 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 requires four separate calls:

curl -v http(s)://HOSTNAME/api/v3/repos/:owner/:repo/pulls/:number curl -v http(s)://HOSTNAME/api/v3/repos/:owner/:repo/pulls/:number/commits curl -v http(s)://HOSTNAME/api/v3/repos/:owner/:repo/issues/:number/comments curl -v http(s)://HOSTNAME/api/v3/repos/:owner/:repo/pulls/:number/reviews

Using the GraphQL API, 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.

Example: 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 } } } } }