Django的QuerySet

  1. values    returns one Queryset with dict ,not model instance
  2. select_related  it is useful for tables which has foreign key .it only excute once.

     

# Hits the database.
e = Entry.objects.get(id=5)

# Hits the database again to get the related Blog object.
b = e.blog

And here’s select_related lookup:

# Hits the database.
e = Entry.objects.select_related('blog').get(id=5)

# Doesn't hit the database, because e.blog has been prepopulated
# in the previous query.
b = e.blog

3.关联对象特殊操作

>>> b = Blog.objects.get(id=1)
>>> e = b.entry_set.create(
...     headline='Hello',
...     body_text='Hi',
...     pub_date=datetime.date(2005, 1, 1)
... )

4.

auto_now无论是你添加还是修改对象，时间为你添加或者修改的时间。

auto_now_add为添加时的时间，更新对象时不会有变动。

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