render.py 文件源码

def _drop_constraint(constraint, autogen_context):
    """
    Generate Alembic operations for the ALTER TABLE ... DROP CONSTRAINT
    of a  :class:`~sqlalchemy.schema.UniqueConstraint` instance.
    """

    types = {
        "unique_constraint": "unique",
        "foreign_key_constraint": "foreignkey",
        "primary_key_constraint": "primary",
        "check_constraint": "check",
        "column_check_constraint": "check",
    }

    if 'batch_prefix' in autogen_context:
        template = "%(prefix)sdrop_constraint"\
            "(%(name)r, type_=%(type)r)"
    else:
        template = "%(prefix)sdrop_constraint"\
            "(%(name)r, '%(table_name)s'%(schema)s, type_=%(type)r)"

    constraint_table = _table_for_constraint(constraint)
    text = template % {
        'prefix': _alembic_autogenerate_prefix(autogen_context),
        'name': _render_gen_name(autogen_context, constraint.name),
        'table_name': _ident(constraint_table.name),
        'type': types[constraint.__visit_name__],
        'schema': (", schema='%s'" % _ident(constraint_table.schema))
        if constraint_table.schema else '',
    }
    return text