由于做Caption要做权限设计。在核心类的设计的时候需要做好权限的基础设计。django 1.7+以后 django.db.modes新增特性 default_permissions，官方文档语焉不详。
决定自己探索下，不想一一分析代码，遂引入bug，直接观察核心线路。
引入bug方法：
class baseModel(models.Model):
#....
class Meta:
default_permissions='add'#should be ('add','change',...)
错误如下：
Traceback (most recent call last):
File "C:Users ommy.yuDesktopCaptainCaptain-mastercodesCaptainmanage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocoremanagement\__init__.py", line 385, in execute_from_command_line
utility.execute()
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocoremanagement\__init__.py", line 377, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocoremanagementase.py", line 288, in run_from_argv
self.execute(*args, **options.__dict__)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocoremanagementase.py", line 338, in execute
output = self.handle(*args, **options)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocoremanagementcommandsmigrate.py", line 165, in handle
emit_post_migrate_signal(created_models, self.verbosity, self.interactive, connection.alias)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocoremanagementsql.py", line 268, in emit_post_migrate_signal
using=db)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodispatchdispatcher.py", line 198, in send
response = receiver(signal=self, sender=sender, **named)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangocontribauthmanagement\__init__.py", line 114, in create_permissions
Permission.objects.using(using).bulk_create(perms)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbmodelsquery.py", line 409, in bulk_create
self._batched_insert(objs_without_pk, fields, batch_size)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbmodelsquery.py", line 938, in _batched_insert
using=self.db)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbmodelsmanager.py", line 92, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbmodelsquery.py", line 921, in _insert
return query.get_compiler(using=using).execute_sql(return_id)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbmodelssqlcompiler.py", line 920, in execute_sql
cursor.execute(sql, params)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbackendsutils.py", line 81, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbackendsutils.py", line 65, in execute
return self.cursor.execute(sql, params)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbutils.py", line 94, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbackendsutils.py", line 65, in execute
return self.cursor.execute(sql, params)
File "C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbackendssqlite3ase.py", line 486, in execute
return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: columns content_type_id, codename are not unique
直接在最终的文件C:Python27libsite-packagesdjango-1.7.2-py2.7.eggdjangodbackendssqlite3ase.py里面加入print xxx之类的语句。如下：
def execute(self, query, params=None):
if params is None:
return Database.Cursor.execute(self, query)
query = self.convert_query(query)
print query,params#在这里添加了print
return Database.Cursor.execute(self, query, params)
再次migrate，并观察sql：
由于sql过多，只抓出insert的sql，如下:
INSERT INTO "auth_permission" ("name", "content_type_id", "codename") SELECT ? AS "name", ? AS "content_type_id", ? AS "codename" UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? ... ( u'Can add tag', 7, u'add_tag', u'Can change tag', 7, u'change_tag', u'Can delete tag', 7, u'delete_tag', ... )
即写表auth_permission ,django的权限表，可以参考这里。
经过反复的try发现，default_permissions只是取出 default_permissions[0],default_permissions[1],default_permissions[2]然后将其插入到数据表auth_permission里面。而且版本1.7.2的还有bug：
case 1. str类型赋值
default_permissions='abcde'
sql如下，以上代码为抽象基类中的meta类，对于子类(Tag,ContentType,Menu,Page)来说，只有最后一个Page起到作用了（id为10）
INSERT INTO "auth_permission" ("name", "content_type_id", "codename") SELECT ? AS "name", ? AS "content_type_id", ? AS "codename" UNION ALL SELECT ?, ?, ? UNION A LL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? (u'Can add tag', 7, u'add_tag', u'Can change tag', 7, u'change_tag', u'Can delete tag', 7, u'delete_tag', u'Can add content type', 8, u'add_contenttype', u'Can change content type', 8, u'change_contenttype', u'Can delete content type', 8, u'delete_contenttype', u'Can add menu', 9, u'add_menu', u'Can change menu', 9, u'change_menu', u'Can delete menu', 9, u'delete_menu', u'Can a page', 10, 'a_page', u'Can b page', 10, 'b_page', u'Can c page', 10, 'c_page', u'Can d page', 10, 'd_page', u'Can e page', 10, 'e_page')
case 2. tuple/list ,长度小于3
抽象基类default_permissions属性
default_permissions=('add', 'change')
生成的sql代码：
INSERT INTO "auth_permission" ("name", "content_type_id", "codename") SELECT ? AS "name", ? AS "content_type_id", ? AS "codename" UNION ALL SELECT ?, ?, ? UNION A LL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? UNION ALL SELECT ?, ?, ? (u'Can add tag', 7, u'add_tag', u'Can change tag', 7, u'change_tag', u'Can delete tag', 7, u'delete_tag', u'Can add content type', 8, u'add_contenttype', u'Can change content type', 8, u'change_contenttype', u'Can delete content type', 8, u'delete_contenttype', u'Can add menu', 9, u'add_menu', u'Can change menu', 9, u'change_menu', u'Can delete menu', 9, u'delete_menu', u'Can add page', 10, 'add_page', u'Can change page', 10,'change_page')
跟case 1 差不多，有作用，有bug。
结论：
往表auth_permissions里面插入记录而已。
鉴于只对子类中的最后一个模型起作用（包括permissions属性），因此不能作为公共属性。