Django ORM原始删除查询不删除记录

Question

我正在使用raw_sql查询，以方便我保持数据库最小化我删除额外的记录。通过这个查询

#d is from a loop and has values
res=MyModel.objects.raw("DELETE FROM mydb_mymodel WHERE mydb_mymodel.s_type = '%s' and mydb_mymodel.barcode = '%s' and mydb_mymodel.shopcode = '%s' and mydb_mymodel.date = '%s'" ,[d.s_type,d.barcode,d.shopcode,d.date])

它不是删除数据库中的记录而是

当我做res.query并从postgres控制台运行它它的工作原理！

是的，我可以使用

MyModel.objects.filter(s_type=d.s_type,barcode=d.barcode,
shopcode=d.shopcode,date=d.date).delete()

但是我在raw_sql中缺少什么？

Answer 1

.raw(..)并没有急切地执行，就像大多数Django ORM查询懒洋洋地执行一样。因此，它返回一个带有查询的RawQuerySet对象。例如：

>>> User.objects.raw('BLA BLA BLA', [])
<RawQuerySet: BLA BLA BLA>

像BLA BLA BLA这样的查询没有任何意义：数据库会出错，但我们仍然会检索RawQuerySet。

你可以通过例如迭代它来强制评估，然后我们得到：

>>> list(User.objects.raw('BLA BLA BLA', []))
Traceback (most recent call last):
  File "/djangotest/env/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/djangotest/env/lib/python3.6/site-packages/django/db/backends/mysql/base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "/djangotest/env/lib/python3.6/site-packages/MySQLdb/cursors.py", line 250, in execute
    self.errorhandler(self, exc, value)
  File "/djangotest/env/lib/python3.6/site-packages/MySQLdb/connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File "/djangotest/env/lib/python3.6/site-packages/MySQLdb/cursors.py", line 247, in execute
    res = self._query(query)
  File "/djangotest/env/lib/python3.6/site-packages/MySQLdb/cursors.py", line 412, in _query
    rowcount = self._do_query(q)
  File "/djangotest/env/lib/python3.6/site-packages/MySQLdb/cursors.py", line 375, in _do_query
    db.query(q)
  File "/djangotest/env/lib/python3.6/site-packages/MySQLdb/connections.py", line 276, in query
    _mysql.connection.query(self, query)
_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'BLA BLA BLA' at line 1")

所以list(..)强制评估，现在数据库当然会产生错误。但是，即使它是有效的DELETE查询，它仍然会引发错误，因为此类查询不会返回任何记录。

为了进行DELETE调用，Django手册指定你应该use a cursor [Django-doc]：

from django.db import connection

with connection.cursor() as cursor:
    cursor.execute(
        "DELETE FROM mydb_mymodel WHERE s_type = '%s' AND barcode = '%s' AND shopcode = '%s' AND date = '%s'" ,
        [d.s_type,d.barcode,d.shopcode,d.date]
    )

但我认为指定它可能要简单得多：

MyModel.objects.filter(
    s_type=d.s_type,
    barcode=d.barcode,
    shopcode=d.shopcode,
    date=d.date
).delete()

这将构造一个DELETE查询，并正确序列化参数。 .delete()查询是急切地进行的，因此上述讨论错误的几率要低很多：如果ORM正确实现，那么我们就不用担心了。