Getting started with the Git Database API

Overview

This basically allows you to reimplement a lot of Git functionality over our API - by creating raw objects directly into the database and updating branch references you could technically do just about anything that Git can do without having Git installed.

Git Database API functions will return a 409 Conflict if the Git repository is empty or unavailable. An unavailable repository typically means GitHub Enterprise is in the process of creating the repository. For an empty repository, you can use the "Create or update file contents" endpoint to create content and initialize the repository so you can use the Git Database API. Contact your GitHub Enterprise site administrator if this response status persists.

For more information on the Git object database, please read the Git Internals chapter of the Pro Git book.

As an example, if you wanted to commit a change to a file in your repository, you would:

• Get the current commit object
• Retrieve the tree it points to
• Retrieve the content of the blob object that tree has for that particular file path
• Change the content somehow and post a new blob object with that new content, getting a blob SHA back
• Post a new tree object with that file path pointer replaced with your new blob SHA getting a tree SHA back
• Create a new commit object with the current commit SHA as the parent and the new tree SHA, getting a commit SHA back
• Update the reference of your branch to point to the new commit SHA

It might seem complex, but it's actually pretty simple when you understand the model and it opens up a ton of things you could potentially do with the API.

Checking mergeability of pull requests

A consuming API needs to explicitly request a pull request to create a test merge commit. A test merge commit is created when you view the pull request in the UI and the "Merge" button is displayed, or when you get, create, or edit a pull request using the REST API. Without this request, the merge Git refs will fall out of date until the next time someone views the pull request.

If you are currently using polling methods that produce outdated merge Git refs, then GitHub recommends using the following steps to get the latest changes from the base branch (usually master):

1. Receive the pull request webhook.
2. Call GET /repos/{owner}/{repo}/pulls/{pull_number} to start a background job for creating the merge commit candidate.
3. Poll your repository using GET /repos/{owner}/{repo}/pulls/{pull_number} to see if the mergeable attribute is true or false. You can use Git directly or GET /repos/{owner}/{repo}/git/refs/{ref} for updates to merge Git refs only after performing the previous steps.