Independent Named BranchesΒΆ

Alembic supports named branches, but its syntax is hard to remember and verbose. Flask-Alembic makes it easier by providing a central configuration for branch names and revision directories and simplifying the syntax to the revision command.

Alembic allows configuration of multiple version locations. version_locations is a list of directories to search for migration scripts. Flask-Alembic extends this to allow tuples as well as strings in the list. Each tuple is a (branch, directory) pair. The script_location is automatically given the label default and added to the version_locations.

    "version_locations": [
        # not a branch, just another search location
        # posts branch migrations will be placed here
        ("posts", "/path/to/posts_extension/migrations"),
        # relative paths are relative to the application root
        ("users", "users/migrations"),

The revision command takes a --branch option (defaults to default). This takes the place of specifying --parent, --label, and --path. This will automatically start the branch from the base revision, label the revision correctly, and place the revisions in the correct location.

$ flask db revision --branch users "create user model"

# equivalent to (if branch is new)
$ alembic revision --autogenerate --head base --branch-label users --version-path users/migrations -m "create user model"

# or (if branch exists)
$ alembic revision --autogenerate --head users@head -m "create user model"