c# - How to manage Migrations in a project with multiple branches?

Question

I have an ASP.NET MVC3 project that uses Entity Framework 4.3 with the code-first approach. I use Migrations to keep the database up-to-date.

The project is under source-control and I have a number of branches. What I just realized is that there will be a problem when I want to merge one of my branches into the master. Since I have created migration-files in both branches, there will be overlapping migrations when I merge, which will probably cause conflicts.

Is there a good way to manage Migrations in a project with multiple branches?

Update

One way would be to merge, then delete all migration-files created while the branches were separate, and then create one new migration file that holds all changes from the time the branch was created until it was merged back in. This would work for the dev-environment where you can dump the database and re-build it with all the migration-files. The problem then would be the live-environment. Since you couldn't roll back to the time the branch was created without the risk of loosing data, there will be a conflict when you try to use your new migration-file to update the live database.

Answer 1

Edit: a colleague of mine discovered an easier with to do this, I left my original answer at the bottom for completeness.

(VERY IMPORTANT) migrations in live environment must not conflict with ones in your current branch, otherwise you need to redo all your migrations and resolve data model change conflicts by hand.

1. restore your development database with live environment data
2. run update-database, it should run migrations from your branch, and complain about 'unable to update database to match the current model blah blah..'
3. run add-migration MergeBranchBToMaster -ignoreChanges, this will create an empty migration.
4. run update-database again
5. push your changes

The magic in step 3 basically tells EF to shutup about mismatched models, hence be very sure that your migrations do not conflict with ones in live environment. If they do, you can always create SQL scripts for pushing the missing migrations (which is actually the preferred method).

Original Answer

I have found a fairly straight-forward solution based on @Ladislav Mrnka's answer. This will work with live environment[1], you just have to be careful not to change any deployed migrations.

1. Before Merge, take note of the migration you added (MyMigration), and its previous migration (BaseMigration)

2. Merge branches in git

3. Open Package Manager Console, and run: UPDATE-DATABASE -TargetMigration:BaseMigration. This will revert your database to the state before any of the conflicted migrations are applied

4. Delete your local migration (MyMigration)

5. Run: UPDATE-DATABASE. This will apply all newer migrations done in other branches.

6. Run: ADD-MIGRATION MyMigration. This will re-generate your local migration based on current state of database, like git -rebase.

7. Run: UPDATE-DATABASE. Update database with you local migration.

This also works if you have multiple local migrations, but it will merge them all into a single one.

[1] by working with live environment, I mean that the generated migration can be applied to live environment which may already have some/all of the other branches' migrations applied. The steps themselves are purely for development purpose.