migration.py 文件源码

def get_current_revision(self):
        """Return the current revision, usually that which is present
        in the ``alembic_version`` table in the database.

        This method intends to be used only for a migration stream that
        does not contain unmerged branches in the target database;
        if there are multiple branches present, an exception is raised.
        The :meth:`.MigrationContext.get_current_heads` should be preferred
        over this method going forward in order to be compatible with
        branch migration support.

        If this :class:`.MigrationContext` was configured in "offline"
        mode, that is with ``as_sql=True``, the ``starting_rev``
        parameter is returned instead, if any.

        """
        heads = self.get_current_heads()
        if len(heads) == 0:
            return None
        elif len(heads) > 1:
            raise util.CommandError(
                "Version table '%s' has more than one head present; "
                "please use get_current_heads()" % self.version_table)
        else:
            return heads[0]