a54c57ada3f5_removes_useless_indexes.py 文件源码

def upgrade():
    bind = op.get_bind()
    # NOTE(sileht): mysql can't delete an index on a foreign key
    # even this one is not the index used by the foreign key itself...
    # In our case we have two indexes fk_resource_history_id_resource_id and
    # and ix_resource_history_id, we want to delete only the second, but mysql
    # can't do that with a simple DROP INDEX ix_resource_history_id...
    # so we have to remove the constraint and put it back...
    if bind.engine.name == "mysql":
        op.drop_constraint("fk_resource_history_id_resource_id",
                           type_="foreignkey", table_name="resource_history")

    for table, colname in resource_tables + history_tables + other_tables:
        op.drop_index("ix_%s_%s" % (table, colname), table_name=table)

    if bind.engine.name == "mysql":
        op.create_foreign_key("fk_resource_history_id_resource_id",
                              "resource_history", "resource", ["id"], ["id"],
                              ondelete="CASCADE")