当在odoo页面新建一条记录的时候，前端会通过rpc调用后端模型的default_get 函数，根据前端传入的字段列表，来获取相对应的字段默认值。

	# odoo/models.py@api.modeldef default_get(self, fields_list):""" default_get(fields_list) -> default_valuesReturn default values for the fields in ``fields_list``. Defaultvalues are determined by the context, user defaults, and the modelitself.:param list fields_list: names of field whose default is requested:return: a dictionary mapping field names to their corresponding default values,if they have a default value.:rtype: dict.. note::Unrequested defaults won't be considered, there is no need to return avalue for fields whose names are not in `fields_list`."""defaults = {}parent_fields = defaultdict(list)ir_defaults = self.env['ir.default'].get_model_defaults(self._name)for name in fields_list:# 1. look up contextkey = 'default_' + nameif key in self._context:defaults[name] = self._context[key]continue# 2. look up ir.defaultif name in ir_defaults:defaults[name] = ir_defaults[name]continuefield = self._fields.get(name)# 3. look up field.defaultif field and field.default:defaults[name] = field.default(self)continue# 4. delegate to parent modelif field and field.inherited:field = field.related_fieldparent_fields[field.model_name].append(field.name)# convert default values to the right format## we explicitly avoid using _convert_to_write() for x2many fields,# because the latter leaves values like [(Command.LINK, 2),# (Command.LINK, 3)], which are not supported by the web client as# default values; stepping through the cache allows to normalize# such a list to [(Command.SET, 0, [2, 3])], which is properly# supported by the web clientfor fname, value in defaults.items():if fname in self._fields:field = self._fields[fname]value = field.convert_to_cache(value, self, validate=False)defaults[fname] = field.convert_to_write(value, self)# add default values for inherited fieldsfor model, names in parent_fields.items():defaults.update(self.env[model].default_get(names))return defaults

1、该函数的作用

    函数文档说的很清楚了，我在赘述一遍。该函数根据传入的字段名返回响应的默认值，默认值是由context，用户定义以及模型本身决定的。输入参数： field_list  字段名称列表。返回值： 一个字典，key是字段名称，value是该字段的默认值注意： 该函数只返回请求列表中的字段的默认值。至于有哪些字段，是由前端视图决定的。

2、设置默认值的四种方式

从代码中可以看到，获取字典的默认值，按照优先级有四种方式：

2.1 上下文context

action

        <record id="action_move_out_invoice_type" model="ir.actions.act_window"><field name="name">Invoices</field><field name="res_model">account.move</field><field name="view_mode">tree,kanban,form</field><field name="view_id" ref="view_out_invoice_tree"/><field name="search_view_id" ref="view_account_invoice_filter"/><field name="domain">[('move_type', '=', 'out_invoice')]</field><field name="context">{'default_move_type': 'out_invoice'}</field><field name="help" type="html"><p class="o_view_nocontent_smiling_face">Create a customer invoice</p><p>Create invoices, register payments and keep track of the discussions with your customers.</p></field></record>

2.2 ir.default

@api.modeldef get(self, model_name, field_name, user_id=False, company_id=False, condition=False):""" Return the default value for the given field, user and company, or``None`` if no default is available.:param model_name::param field_name::param user_id: may be ``False`` for all users, ``True`` for thecurrent user, or any user id:param company_id: may be ``False`` for all companies, ``True`` forthe current user's company, or any company id:param condition: optional condition that restricts theapplicability of the default value; this is anopaque string, but the client typically usessingle-field conditions in the form ``'key=val'``."""if user_id is True:user_id = self.env.uidif company_id is True:company_id = self.env.company.idfield = self.env['ir.model.fields']._get(model_name, field_name)default = self.search([('field_id', '=', field.id),('user_id', '=', user_id),('company_id', '=', company_id),('condition', '=', condition),], limit=1)return json.loads(default.json_value) if default else None

从代码看， 可以对模型中的某一字典，根据不同的用户、公司、条件设置不同的默认值。
但是实际开发中很少用。

2.3 字段的默认值

这是最常见的设置默认值的一种方式
有三种设置方法：
1、 直接设置

active = fields.Boolean(default=True)

2、设置为一个函数

example_date = fields.Date(string='Date example', default=_default_example_date, store=False)

3 设置为lamda函数

 user_id = fields.Many2one('res.users', default= lambda self: self.env.user) 

2.4 通过委托继承的父表的默认值(_inherits)

关于委托继承，这里就不具体描述了。 简单理解就是数据存储在父表中，但是可以当自己的字段用。
通过一个many2one字段进行关联。

3 重写default_get

某些场景下，我们可以model中重写这个函数，加上我们自己的逻辑，比如：

    def default_get(self, fields_list):# 先调用父类方法defaults = super().default_get(fields_list)# 然后再执行自己的逻辑去对defaults 进行修改，最后再将它返回。if 'journal_id' in defaults and 'date' in fields_list:last_line = self.search([('journal_id', '=', defaults.get('journal_id')),('state', '=', 'posted'),], limit=1)statement = last_line.statement_idif statement:defaults.setdefault('date', statement.date)elif last_line:defaults.setdefault('date', last_line.date)return defaults