浅析django的abstract,proxy, managed
django.db.models.Model 的 Meta参数
参数 | 类型 | 说明 | 继承 |
abstract | boolean | 是否建表 | 不继承,子类自动充值为默认值(False) |
managed | boolean | 是否自动建表 | 不继承,子类自动充值为默认值(True) |
proxy | boolean | 是否为代理类(不建表) | 不继承,子类自动充值为默认值(False) |
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class Author(models.Model): first_name = models.CharField(max_length = 30 ) last_name = models.CharField(max_length = 40 ) email = models.EmailField(blank = True ,verbose_name = 'e-mail' ) def __unicode__( self ): return u '%s %s' % ( self .first_name, self .last_name) |
代理类 AuthorProxy
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class AuthorProxy(Author): class Meta: proxy = True |
代理类子类 AuthorProxy2
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class AuthorProxy2(AuthorProxy): pass |
通过sqlall查看(django 1.6.5),建表如下:
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CREATE TABLE "books_authorproxy2" ( "author_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "books_author" ( "id" ) DEFERRABLE INITIALLY DEFERRED ); |
因此,可以断定,proxy在继承中的特性跟abstract一样。
将以上代码中的proxy换成managed ,并设置为 False,经测试,生成sql如下:
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CREATE TABLE "books_authorproxy2" ( "authorproxy_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "books_authorpoxy" ( "author_ptr_id" ) DEFERRABLE INITIALLY DEFERRED ); |
即,managed不会继承到子类,子类会默认重置为True
用途
proxy or managed?
官方是这么说的:
So, the general rules are:
1. If you are mirroring an existing model or database table and don’t want all the original database table columns, use Meta.managed=False. That option is normally useful for modeling database views and tables not under the control of Django.
2. If you are wanting to change the Python-only behavior of a model, but keep all the same fields as in the original, use Meta.proxy=True. This sets things up so that the proxy model is an exact copy of the storage structure of the original model when data is saved.
即,通常:
1. 如果你要映射模型到已经存在的数据库,使用managed=False, 这适合不在django控制之下的数据库表和视图。
2. 如果只想要给模型修改python行为,而不需要改变任何字段,使用 proxy=True, 这会保持模型类的数据跟原始表结构一样(实际上就是一个表)
abstract
基本上,父类(abstract)的字段会拷贝到子类的每一个表中(如果子类没有设置Meta.abstract=True), 因此适合的情形,比如给所有表增加一些共性字段,比如创建人等信息。