在SQLAlchemy中选择NULL值

Question

这是我的(PostgreSQL)表 -

test=> create table people (name varchar primary key,
                            marriage_status varchar) ; 

test=> insert into people values ('Ken', 'married');
test=> insert into people values ('May', 'single');
test=> insert into people values ('Joe', NULL);

我想选择被所有的人不知道要结婚了,即包括那些NULL marriage_status.

这并不能正常工作-

test=> select * from people where marriage_status != 'married' ; 
 name | marriage_status 
------+-----------------
 May  | single
(1 row)

当然这样做 -

test=> select * from people where marriage_status != 'married'
       or marriage_status is NULL ; 
 name | marriage_status 
------+-----------------
 May  | single
 Joe  | 

问题是我从SQLAlchemy访问它 -

...filter(or_(people.marriage_status!='married',
              people.marriage_status is None))

被翻译成 -

SELECT people.name as name,
       people.marriage_status as marriage_status
FROM people 
WHERE people.marriage_status != %(status_1)s OR False
sqlalchemy.engine.base.Engine.... {'status_1': 'married'}

而且也没有工作-

test=> select * from people where marriage_status != 'married'
       or False; 
 name | marriage_status 
------+-----------------
 May  | single
(1 row)

也不 -

test=> select * from people where marriage_status != 'married'
       or NULL; 
 name | marriage_status 
------+-----------------
 May  | single
(1 row)

我应该如何通过SQLAlchemy选择NULL值？

Answer 1

(由指示@augurar):因为SQLAlchemy的使用魔术方法(运算符重载)创建SQL结构,但它只能处理操作,如!=或==,但不能一起工作is(这是一个非常有效的Python结构).

因此,要使其与sqlalchemy一起使用,您应该使用:

...filter(or_(people.marriage_status!='married', people.marriage_status == None))

,基本上取代了is None用== None.在这种情况下,您的查询将正确转换为以下SQL:

SELECT people.name AS people_name, people.marriage_status AS people_marriage_status 
FROM people 
WHERE people.marriage_status IS NULL OR people.marriage_status != ?

请参阅IS NULL中的文档.

Answer 2

从SQLAlchemy 0.7.9开始,您可以使用is_该列的方法.

过滤器表达式如:

filter(or_(people.marriage_status!='married', people.marriage_status.is_(None)))

将生成参数化的SQL:

WHERE people.marriage_status != %(status_1)s OR people.marriage_status IS NULL

Answer 3

一种优雅的编写方法是使用 is_ 和 is_not，如以下示例所示：

query.filter(people.student.is_not(None)) 
query.filter(people.student.is_(None)) 

Answer 4

这个问题很老了，但为了完整起见，这里我更喜欢可读的版本：

import sqlalchemy as sa

query.filter(people.marriage_status == sa.null()) 
query.filter(people.marriage_status != sa.null())