tagging a version of your domain model
To migrate your data, you will first need to tag two versions of your domain model. We call the first version the initial version. That’s the version that matches the current state of the database. The second is the final version. That’s the version that matches the desired state of the database. In a typical scenario, the initial version is what is running on production, and the final version is the version that you wish to release to production.
To tag the current version of your domain model as “versionX”, run the following command in SBT:
createVersionTag versionX
This will make a copy of your domain model code into a new package versionX. This new package will
be a sub-package of the migrationsPackage we set up in SBT in the last section. It’s
not a strict copy; all of the package and import statements that reference your domain model
package will be adjusted to reference the new versionX package. At this point, you will want to
run sbt compile to make sure the tagging process went smoothly.
Ideally, you would have tagged the initial version of your model right around the time that you did your last production release. But if not, that’s okay. You simply need to find the correct version from within source control, tag there, and bring the tagged version up to the version control head. With a modern source control system such as Git, this can be accomplished like so:
- Identify a commit along your master branch that has the correct model version. Perhaps you put a version control tag there?
- Check out that commit, and create a new branch from there.
- Create the model version tag on that branch, and commit the changes.
- Check out your master branch again.
- Merge in the branch you just created.
If you already have a release branch, you could just use that branch. But take care to make sure that everything else on the release branch is merged into master. Otherwise, merging your release branch to master may bring in some unwanted changes. Another possibility for accomplishing this is to cherry pick the single commit where you created your version tag.