In this guide, we’ll explore how to create and manage merge requests, set up code reviews, and configure approval workflows in GitLab. By the end, you’ll be equipped to use merge requests effectively for your projects.

What Are GitLab Merge Requests?

A merge request (MR) is a feature in GitLab that enables developers to propose changes to a codebase. It’s more than just merging branches—it serves as a platform for reviewing, discussing, and refining code before it’s merged into the target branch.

Key Features of Merge Requests:

  • Code Review: Collaborate with team members to ensure quality.
  • Approvals: Define mandatory approvals before merging changes.
  • CI/CD Integration: Automatically run pipelines to validate changes.
  • Discussions: Add inline comments to suggest improvements or identify issues.

Creating a Merge Request

Here’s how to create a merge request in GitLab:

  1. Push Changes: Commit and push your changes to a feature branch in your repository: 
    git checkout -b feature/new-feature
# Make changes, then commit and push
git add .
git commit -m "Add new feature"
git push origin feature/new-feature
  2. Navigate to Merge Requests: In GitLab, go to Merge Requests in your project’s sidebar.
  3. Create New MR: Click New Merge Request, select the source branch (e.g., feature/new-feature) and the target branch (e.g., main).
  4. Fill in Details:
    • Add a descriptive title and summary for the MR.
    • Assign reviewers or approvers.
    • Set labels and milestones if needed.
  5. Submit MR: Click Create Merge Request to initiate the review process.

Code Reviews in Merge Requests

Code reviews are a critical part of the merge request process. They ensure that changes meet quality standards and align with project requirements. Here’s how to perform a code review in GitLab:

  1. Open the MR: Navigate to the merge request and review the summary and associated commits.
  2. Review the Changes: Click on the Changes tab to view the diff between the source and target branches.
  3. Add Comments: Highlight lines of code and add inline comments to suggest improvements or ask questions.
  4. Resolve Discussions: Once the author addresses feedback, resolve the discussions to keep the MR clean.

Approval Workflows

GitLab allows you to enforce approval rules for merge requests. This ensures that changes are reviewed and approved before merging. To set up approval workflows:

  1. Navigate to Project Settings: Go to Settings > General > Merge Request Approvals.
  2. Configure Approval Rules:
    • Set the minimum number of required approvals.
    • Specify eligible approvers (e.g., specific users or groups).
  3. Save Changes: Click Save to apply the approval rules.

Once configured, the MR cannot be merged until it meets the required approvals.

Example: Merge Request Workflow with CI/CD

Here’s a typical workflow for using merge requests with CI/CD:

  1. Create a new branch and implement changes.
  2. Push the branch to the repository.
  3. Create a merge request and submit it for review.
  4. GitLab automatically triggers pipelines to validate the changes.
  5. Reviewers review the code and provide feedback.
  6. Once all feedback is addressed and approvals are obtained, merge the MR into the target branch.

Best Practices for Using Merge Requests

Follow these best practices to make the most of GitLab merge requests:

  • Use Descriptive Titles and Summaries: Clearly explain the purpose and scope of the MR.
  • Commit Frequently: Break changes into smaller, meaningful commits for easier review.
  • Enforce Approval Rules: Require at least one or two approvals for critical changes.
  • Integrate CI/CD: Automate tests and validations to catch issues early.
  • Resolve Discussions: Address all comments and mark discussions as resolved before merging.

Example: Enforcing Approval Rules in .gitlab-ci.yml

Here’s how you can enforce CI/CD checks and approval rules in a pipeline:

stages:
  - test
  - review
  - deploy

test-job:
  stage: test
  script:
    - dotnet test

review-job:
  stage: review
  script:
    - echo "Awaiting approval..."
  when: manual
  allow_failure: false
  only:
    - merge_requests

deploy-job:
  stage: deploy
  script:
    - echo "Deploying to production..."
  rules:
    - if: '$CI_COMMIT_BRANCH == "main"'
      when: always

In this example, the review-job waits for manual approval before deployment.

Conclusion

GitLab merge requests are a powerful tool for maintaining code quality and fostering collaboration. By using features like code reviews, approvals, and CI/CD integration, you can streamline your development workflow and deliver high-quality software. Start implementing best practices for merge requests in your GitLab projects today.