makemigrations.py

from django.core.management.commands.makemigrations import Command as BaseCommand  # noqa: E571


DEFAULT_MIGRATION_NAME = 'auto'


class Command(BaseCommand):
    """
    Overrides default `makemigrations` command so we provide a fixed default
    name for migrations. Instead of appending the "auto" + timestamp, we just
    append "auto" or what is defined in `DEFAULT_MIGRATION_NAME`.

    The reason for this change is to make migration names deterministic, so
    conflicts or migration overlaps can be detected and blocked by Git, until
    conflicts are resolved.

    This is essentially useful for our specific workflow of "develop" branch
    being always in a deployable state. Without this change, it would be
    possible for two different PRs merge into "develop" without notice, as
    migration names are always suffixed by timestamp and will rarely conflict.
    Putting "develop" in a non-deployable state, where an action needs to be
    taken, to merge the two conflicting migrations.

    The code below, basically mocks the `migration_name` property, adding a
    default value to it, determined by `DEFAULT_MIGRATION_NAME`.

    Django version: 1.8 (branch stable/1.8.x)
    File: django/core/management/commands/makemigrations.py
    Line: 45

    > self.migration_name = options.get('name', None)

    The code above will call the `migration_name` setter, that will hold the
    custom migration name, if provided. Whenever this property is used across
    the same file, it will call the `migration_name` property defined below,
    which defaults to `DEFAULT_MIGRATION_NAME` in case `_migration_name` is
    not provided.

    This code seems to be valid up to branch stable/2.1.x
    """
    @property
    def migration_name(self):
        return getattr(self, '_migration_name', DEFAULT_MIGRATION_NAME)

    @migration_name.setter
    def migration_name(self, name):
        if name:
            # Only override the migration name when a custom name is provided
            self._migration_name = name