Django之F与Q查询

from django.db.models import F,Q
# 1.查询库存数大于卖出数的书籍
res = models.Book.objects.filter(kucun__gt=F(‘maichu‘))
print(res)  #<QuerySet [<Book: Book object>]>

# 2.将所有书的价格提高100
models.Book.objects.update(price=F(‘price‘) + 100)
"""
帮你获取到表中某个字段对应的值
"""

# 查询书的名字是python入门或者价格是1000的书籍
# res = models.Book.objects.filter(title=‘水浒传‘,price=1100)  # and关系
# res = models.Book.objects.filter(Q(title=‘python入门‘),Q(price=1100))  # 逗号也是and关系
res = models.Book.objects.filter(Q(title=‘西游记‘)|Q(price=1100))  # |是or关系
# res = models.Book.objects.filter(~Q(title=‘水浒传‘))  # ~是not关系
print(res)
print(res.query)

q = Q()
q.connector = ‘or‘ # q对象默认是and关系 可以通过connector改变or
q.children.append((‘title‘,‘三国‘))
q.children.append((‘price‘,‘1100‘))

res = models.Book.objects.filter(q)
print(res)

from django.db.models import F,Q

F  针对自己单表中字段的比较和处理
models.Book.objects.filter(good__gt=F(‘comment‘)*2)
models.Book.objects.all().update(price=F(‘price‘)+1)

Q    &  |  非~
filter(Q(xx=11)|Q(ss=22)&Q(oo=33))
filter(Q(Q(xx=11)|Q(ss=22))&Q(oo=33))  &优先级高
filter(Q(Q(xx=11)|Q(ss=22))&Q(oo=33),name=‘dd‘)  
```

执行原生sql(了解)

```
models.Publish.objects.raw(‘原生sql‘)

from django.db import connection
cursor = connection.cursor()
cursor.excute(sql,[1,])
cursor.fetchall()
```

展示sql的

```
models.Book.objects.filter(good__gt=F(‘comment‘)*2)
from django.db import connection 
print(connection.queries)

```