Django--filter()-字段查找(双下划线的使用详解)
在了解django中的字段查找的同时，让我们先熟悉一下比较符：
大于--gt-(greater than) 小于--lt-(less than) 等于--eq-(equal) 大于等于--gte 小于等于--lte
>>> from queryset_demo.models import Blog,Author,Entry >>> entry = Entry.objects.filter(pub_date__lte='2017-01-01') >>> entry <QuerySet [<Entry: python-2015>, <Entry: python-2014>, <Entry: python-4>]> >>> [d.id for d in entry] # 返回数据的id [5, 6, 7]
对应的sql语句为
mysql> select * from queryset_demo_entry -> ; +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | 1 | python | This is a demo | 2018-07-11 | 2018-07-14 | 10 | 29 | 23 | 4 | | 2 | python | django | 2018-07-12 | 2018-07-28 | 2 | 2 | 2 | 2 | | 3 | python-2017 | djagoddd | 2017-06-01 | 2017-08-14 | 55 | 676 | 88 | 3 | | 4 | python-2017 | django-ll | 2017-03-14 | 2017-07-14 | 22 | 33 | 44 | 1 | | 5 | python-2015 | ddd | 2015-07-14 | 2015-07-14 | 33 | 33 | 33 | 1 | | 6 | python-2014 | ddd | 2014-07-14 | 2014-07-14 | 22 | 33 | 33 | 3 | | 7 | python-4 | ddd | 2014-07-14 | 2018-07-04 | 66 | 66 | 66 | 4 | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ 7 rows in set (0.00 sec) mysql> select * from queryset_demo_entry where pub_date<2017-01-01; Empty set, 1 warning (0.00 sec) mysql> select * from queryset_demo_entry where pub_date<'2017-01-01'; +----+-------------+-----------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+-------------+-----------+------------+------------+------------+-------------+--------+---------+ | 5 | python-2015 | ddd | 2015-07-14 | 2015-07-14 | 33 | 33 | 33 | 1 | | 6 | python-2014 | ddd | 2014-07-14 | 2014-07-14 | 22 | 33 | 33 | 3 | | 7 | python-4 | ddd | 2014-07-14 | 2018-07-04 | 66 | 66 | 66 | 4 | +----+-------------+-----------+------------+------------+------------+-------------+--------+---------+ 3 rows in set (0.00 sec)
对外键ForeignKey的字段查找，同时也是一个特殊的地方就是可以通过单下划线
>>> entry <QuerySet [<Entry: python>, <Entry: python-4>]> >>> type(entry) <class 'django.db.models.query.QuerySet'> >>> [d.id for d in entry] [1, 7]
sql
mysql> select * from queryset_demo_entry -> ; +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | 1 | python | This is a demo | 2018-07-11 | 2018-07-14 | 10 | 29 | 23 | 4 | | 2 | python | django | 2018-07-12 | 2018-07-28 | 2 | 2 | 2 | 2 | | 3 | python-2017 | djagoddd | 2017-06-01 | 2017-08-14 | 55 | 676 | 88 | 3 | | 4 | python-2017 | django-ll | 2017-03-14 | 2017-07-14 | 22 | 33 | 44 | 1 | | 5 | python-2015 | ddd | 2015-07-14 | 2015-07-14 | 33 | 33 | 33 | 1 | | 6 | python-2014 | ddd | 2014-07-14 | 2014-07-14 | 22 | 33 | 33 | 3 | | 7 | python-4 | ddd | 2014-07-14 | 2018-07-04 | 66 | 66 | 66 | 4 | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ 7 rows in set (0.00 sec)
精确查找exact
>>> entry=Entry.objects.get(body_text__exact="This is a demo") >>> entry.id 1 >>> entry=Entry.objects.get(body_text="This is a demo") >>> entry.id 1
sql
mysql> select * from queryset_demo_entry -> ; +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | 1 | python | This is a demo | 2018-07-11 | 2018-07-14 | 10 | 29 | 23 | 4 | | 2 | python | django | 2018-07-12 | 2018-07-28 | 2 | 2 | 2 | 2 | | 3 | python-2017 | djagoddd | 2017-06-01 | 2017-08-14 | 55 | 676 | 88 | 3 | | 4 | python-2017 | django-ll | 2017-03-14 | 2017-07-14 | 22 | 33 | 44 | 1 | | 5 | python-2015 | ddd | 2015-07-14 | 2015-07-14 | 33 | 33 | 33 | 1 | | 6 | python-2014 | ddd | 2014-07-14 | 2014-07-14 | 22 | 33 | 33 | 3 | | 7 | python-4 | ddd | 2014-07-14 | 2018-07-04 | 66 | 66 | 66 | 4 | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ 7 rows in set (0.00 sec) mysql> select * from queryset_demo_entry where body_text ='This is a demo'; +----+----------+----------------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+----------+----------------+------------+------------+------------+-------------+--------+---------+ | 1 | python | This is a demo | 2018-07-11 | 2018-07-14 | 10 | 29 | 23 | 4 | +----+----------+----------------+------------+------------+------------+-------------+--------+---------+ 1 row in set (0.00 sec)
跨表查询
>>> Entry.objects.filter(blog__name='blog_3') <QuerySet [<Entry: python>, <Entry: python-4>]> >>> entry=Entry.objects.filter(blog__name='blog_3') >>> [d.id for d in entry] [1, 7]
sql
mysql> select * from queryset_demo_blog; +----+-----------------+------------------------------+ | id | name | tagline | +----+-----------------+------------------------------+ | 1 | change_new_name | All the latest Beatles news. | | 2 | create_test | This is the wayof create | | 3 | Cheddar Talk | One to Many test | | 4 | blog_3 | this is a test | +----+-----------------+------------------------------+ 4 rows in set (0.00 sec) mysql> select * from queryset_demo_entry -> ; +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | 1 | python | This is a demo | 2018-07-11 | 2018-07-14 | 10 | 29 | 23 | 4 | | 2 | python | django | 2018-07-12 | 2018-07-28 | 2 | 2 | 2 | 2 | | 3 | python-2017 | djagoddd | 2017-06-01 | 2017-08-14 | 55 | 676 | 88 | 3 | | 4 | python-2017 | django-ll | 2017-03-14 | 2017-07-14 | 22 | 33 | 44 | 1 | | 5 | python-2015 | ddd | 2015-07-14 | 2015-07-14 | 33 | 33 | 33 | 1 | | 6 | python-2014 | ddd | 2014-07-14 | 2014-07-14 | 22 | 33 | 33 | 3 | | 7 | python-4 | ddd | 2014-07-14 | 2018-07-04 | 66 | 66 | 66 | 4 | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ 7 rows in set (0.00 sec)
反向查询
通过blog表进行查询
它也可以倒退。要引用“反向”关系，只需使用模型的小写名称即可。
这个例子检索所有Blog具有至少一个对象Entry ，其headline包含'Lennon'：
>>> from queryset_demo.models import * >>> blog = Blog.objects.filter(entry__body_text__contains='dj') >>> blog <QuerySet [<Blog: create_test>, <Blog: Cheddar Talk>, <Blog: change_new_name>]> >>> [d.id for d in blog] [2, 3, 1] >>>
跨越多值关系
使用下划线查找多值得关系
>>> blog = Blog.objects.filter(entry__body_text__contains='dj') >>> blog <QuerySet [<Blog: create_test>, <Blog: Cheddar Talk>, <Blog: change_new_name>]> >>> [d.id for d in blog] [2, 3, 1] >>> blog = Blog.objects.filter(entry__body_text__contains='dj',entry__pub_date__year=2017) >>> [d.id for d in blog] [3, 1] >>> blog = Blog.objects.filter(entry__body_text__contains='dj').filter(entry__pub_date__year=2017) >>> blog_2 = Blog.objects.filter(entry__body_text__contains='dj').filter(entry__pub_date__year=2017) >>> blog_2 <QuerySet [<Blog: Cheddar Talk>, <Blog: change_new_name>]> >>> blog <QuerySet [<Blog: Cheddar Talk>, <Blog: change_new_name>]> >>>
英文：
Suppose there is only one blog that had both entries containing “Lennon” and entries from 2008, but that none of the entries from 2008 contained “Lennon”. The first query would not return any blogs, but the second query would return that one blog.
In the second example, the first filter restricts the queryset to all those blogs linked to entries with “Lennon” in the headline. The second filter restricts the set of blogs further to those that are also linked to entries that were published in 2008. The entries selected by the second filter may or may not be the same as the entries in the first filter. We are filtering the Blog items with each filter statement, not the Entry items.
理解：
数据库进行数据的添加
mysql> mysql> select * from queryset_demo_entry; +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ | 1 | python | This is a demo | 2018-07-11 | 2018-07-14 | 10 | 29 | 23 | 4 | | 2 | python | django | 2018-07-12 | 2018-07-28 | 2 | 2 | 2 | 2 | | 3 | python-2017 | djagoddd | 2017-06-01 | 2017-08-14 | 55 | 676 | 88 | 3 | | 4 | python-2017 | django-ll | 2017-03-14 | 2017-07-14 | 22 | 33 | 44 | 1 | | 5 | python-2015 | ddd | 2015-07-14 | 2015-07-14 | 33 | 33 | 33 | 1 | | 6 | python-2014 | ddd | 2014-07-14 | 2014-07-14 | 22 | 33 | 33 | 3 | | 7 | python-4 | ddd | 2014-07-14 | 2018-07-04 | 66 | 66 | 66 | 4 | | 8 | demo | demo | 2017-06-16 | 2017-05-16 | 33 | 33 | 5 | 2 | | 9 | demo2 | zzddxx | 2017-02-16 | 2017-02-04 | 44 | 33 | 22 | 3 | +----+-------------+----------------+------------+------------+------------+-------------+--------+---------+ 9 rows in set (0.00 sec) mysql> select * from queryset_demo_blog; +----+-----------------+------------------------------+ | id | name | tagline | +----+-----------------+------------------------------+ | 1 | change_new_name | All the latest Beatles news. | | 2 | create_test | This is the wayof create | | 3 | Cheddar Talk | One to Many test | | 4 | blog_3 | this is a test | +----+-----------------+------------------------------+ 4 rows in set (0.01 sec)
shell进行测试
>>> blog = Blog.objects.filter(entry__body_text__contains='dj',entry__pub_date__year=2017) >>> blog <QuerySet [<Blog: Cheddar Talk>, <Blog: change_new_name>]> >>> >>> >>> blog_2 = Blog.objects.filter(entry__body_text__contains='dj').filter(entry__pub_date__year=2017) >>> blog_2 <QuerySet [<Blog: create_test>, <Blog: Cheddar Talk>, <Blog: Cheddar Talk>, <Blog: change_new_name>]> >>> [d.id for d in blog] [3, 1] >>> [d.id for d in blog_2] [2, 3, 3, 1]