How to use the command 'dolt merge' (with examples)

The command dolt merge is a powerful tool used in Dolt, a version control system that handles data similar to how Git handles source code. Dolt allows users to track changes, collaborate, and maintain the history of databases in a seamless and efficient way. The dolt merge command is specifically used to join two or more development histories together. This capability is essential when working with multiple branches, as it allows you to integrate changes from different lines of development into a single branch, ensuring your database remains updated with the latest improvements from various sources.

Use case 1: Incorporate changes from the named commits into the current branch

Code:

dolt merge branch_name

Motivation: When working collaboratively, it is common for developers to work on separate branches to isolate features or fixes. As work progresses, these branches eventually need to be merged back into the main line of development to ensure that all enhancements are available to everyone. This use case exemplifies the straightforward merging of changes from a feature branch, identified by branch_name, into the current branch. This ensures that the current branch gets updated with the new changes made in the branch_name.

Explanation:

• dolt: This is the command-line executable for interacting with Dolt repositories.
• merge: This subcommand takes care of merging changes from another branch.
• branch_name: You provide the name of the branch whose changes you want to merge into your current branch. This is where the development history resides that you want to incorporate.

Example Output:

Successfully merged changes from 'branch_name' into 'current_branch'.

Use case 2: Incorporate changes from the named commits into the current branch without updating the commit history

Code:

dolt merge --squash branch_name

Motivation: Sometimes you need to merge changes, but you prefer not to clutter your commit history with all individual commit logs from the target branch. This is particularly useful for feature branches that had many small or experimental commits. By using the --squash option, all of these changes are combined into one, appearing as a single commit on the main branch, making the history cleaner and easier to manage.

Explanation:

• merge --squash: This combination commands Dolt to merge the changes from the specified branch but to consolidate all those changes into a single commit, instead of preserving the individual commit history.
• branch_name: The source branch from which you are taking changes.

Example Output:

Changes from 'branch_name' have been squashed and are ready to be committed to 'current_branch'.

Use case 3: Merge a branch and create a merge commit even when the merge resolves as a fast-forward

Code:

dolt merge --no-ff branch_name

Motivation: In some cases, a process called “fast-forward” ensues when the current branch is directly ahead of the target branch, integrating changes without creating a new commit. This is beautiful for a streamlined history, but sometimes you want to record the merge operation itself, possibly for auditing or clarity in history. Using --no-ff forces the creation of a merge commit regardless of whether the changes could be applied directly, thus documenting the merge explicitly in your commit history.

Explanation:

• merge --no-ff: This command ensures that the merge results in a new commit being created on the current branch, even if it could have been a simple fast-forward merge.
• branch_name: The source branch containing changes that you want to merge into the current branch.

Example Output:

Merge commit created for 'branch_name' into 'current_branch'.

Use case 4: Merge a branch and create a merge commit with a specific commit message

Code:

dolt merge --no-ff -m "message" branch_name

Motivation: When performing a merge, it may be important to add context or a descriptive message about the changes being integrated. This is helpful for other collaborators to understand the nature of the merge without deciphering commit details. The -m option is used to specify a custom message that accompanies the merge commit, enhancing clarity and communicative efficiency.

Explanation:

• merge --no-ff -m "message": This sequence tells Dolt to create a merge commit containing the custom message you provide, useful for documenting purpose or impact of the merge succinctly.
• branch_name: The branch you are merging from.

Example Output:

Merge commit with message 'message' created for merging 'branch_name' into 'current_branch'.

Use case 5: Abort the current conflict resolution process

Code:

dolt merge --abort

Motivation: Merging branches can sometimes result in conflicts, where the changes in each branch cannot be automatically resolved by Dolt. When this happens, you may need to abort the current merge process, especially if the conflicts are complex or require additional thought. The --abort option is used to rewind any in-progress merge back to the pre-merge state, allowing you to reconsider or choose another approach for resolution.

Explanation:

• merge --abort: This command halts an ongoing merge process and restores the state prior to the start of the merge, a safeguard to recover from unexpected complications during merging.

Example Output:

Merge process aborted. Reverted to pre-merge state.

Conclusion:

The dolt merge command provides a versatile range of functionalities for managing and integrating changes across various branches of a Dolt repository. Whether you need to simply incorporate changes, tidy up your commit history with a squash, enforce documentation with explicit messages, or manage conflicts gracefully, dolt merge empowers users with the necessary tools to handle such tasks efficiently while maintaining a clear and professional developmental workflow.