class BaseModel(object):

    """ Base class for OpenERP models.

    OpenERP models are created by inheriting from this class' subclasses:

    *   :class:`Model` for regular database-persisted models 常用数据库模型

    *   :class:`TransientModel` for temporary data, stored in the database but

        automatically vacuumed every so often 临时模型

    *   :class:`AbstractModel` for abstract super classes meant to be shared by

        multiple inheriting model 抽象模型 不保存

    The system automatically instantiates every model once per database. Those

    instances represent the available models on each database, and depend on

    which modules are installed on that database. The actual class of each

    instance is built from the Python classes that create and inherit from the

    corresponding model.

    Every model instance is a "recordset", i.e., an ordered collection of

    records of the model. Recordsets are returned by methods like

    :meth:`~.browse`, :meth:`~.search`, or field accesses. Records have no

    explicit representation: a record is represented as a recordset of one

    record.

    To create a class that should not be instantiated, the _register class

    attribute may be set to False.

    """

    __metaclass__ = MetaModel

    _auto = True # create database backend

    _register = False # Set to false if the model shouldn't be automatically discovered.

    _name = None

    _columns = {}

    _constraints = []

    _custom = False

    _defaults = {}

    _rec_name = None

    _parent_name = 'parent_id'

    _parent_store = False

    _parent_order = False

    _date_name = 'date'

    _order = 'id'

    _sequence = None

    _description = None

    _needaction = False

    _translate = True # set to False to disable translations export for this model

    # dict of {field:method}, with method returning the (name_get of records, {id: fold})

    # to include in the _read_group, if grouped on this field

    _group_by_full = {}

    # Transience

    _transient = False # True in a TransientModel

    # structure:

    #  { 'parent_model': 'm2o_field', ... }

    _inherits = {}

    # Mapping from inherits'd field name to triple (m, r, f, n) where m is the

    # model from which it is inherits'd, r is the (local) field towards m, f

    # is the _column object itself, and n is the original (i.e. top-most)

    # parent model.

    # Example:

    #  { 'field_name': ('parent_model', 'm2o_field_to_reach_parent',

    #                   field_column_obj, origina_parent_model), ... }

    _inherit_fields = {}

    _table = None

    _log_create = False

    _sql_constraints = []

    # model dependencies, for models backed up by sql views:

    # {model_name: field_names, ...}

    _depends = {}

    CONCURRENCY_CHECK_FIELD = '__last_update'