Django F查询Q查询Only与Defel

from django.db import models

# Create your models here.
class MyCharField(models.Field):
    def __init__(self,max_length,*args,**kwargs):
        self.max_length = max_length
        super().__init__(max_length=max_length,*args,**kwargs)

    def db_type(self, connection):
        return ‘char(%s)‘%self.max_length

class Product(models.Model):
    name = models.CharField(max_length=32)  # 都是类实例化出来的对象
    price = models.DecimalField(max_digits=8,decimal_places=2)
    maichu = models.IntegerField()
    kucun = models.IntegerField()
    info = MyCharField(max_length=32,null=True)  # 改字段可以为空

    choices = ((1,‘男‘),(2,‘女‘),(3,‘其他‘))
    gender = models.IntegerField(choices=choices,default=2)

    res = models.Product.objects.filter(maichu__gt=F(‘kucun‘))
    print(res)
    将所有的商品的价格提高100块
    models.Product.objects.update(price=F(‘price‘)+100)
    将所有商品的名字后面都加一个爆款
    from django.db.models.functions import Concat
    from django.db.models import Value
    models.Product.objects.update(name=Concat(F(‘name‘),Value(‘爆款‘)))

    res = models.Product.objects.filter(price=188.88,name=‘连衣裙爆款‘)
    print(res)
    from django.db.models import F, Q
    res = models.Product.objects.filter(Q(price=188.88),Q(name=‘连衣裙爆款‘))  # and
    res = models.Product.objects.filter(Q(price=188.88)|Q(name=‘连衣裙爆款‘))  # or
    res = models.Product.objects.filter(Q(price=188.88)|~Q(name=‘连衣裙爆款‘))  # not
    混合使用  需要注意的是Q对象必须放在普通的过滤条件前面
    res = models.Product.objects.filter(~Q(name=‘连衣裙爆款‘),price=188.88)  # not
    print(res)

    Q对象补充(******)
    from django.db.models import F, Q
    q = Q()
    q.connector = ‘or‘  # 通过这个参数可以将Q对象默认的and关系变成or
    q.children.append((‘price‘,188.88))
    q.children.append((‘name‘,‘高跟鞋爆款‘))
    res = models.Product.objects.filter(q)  # Q对象查询默认也是and
    print(res)

    from django.db import transaction
    from django.db.models import F
    with transaction.atomic():
        # 在with代码块儿写你的事务操作
        models.Product.objects.filter(id=1).update(kucun=F(‘kucun‘)-1)
        models.Product.objects.filter(id=1).update(maichu=F(‘maichu‘)+1)

    # 写其他代码逻辑
    print(‘hahah‘)

  only与defer 结果拿到的是一个对象  两者是相反的

    res = models.Product.objects.values(‘name‘)
    res = models.Product.objects.only(‘name‘)
    res = models.Product.objects.defer(‘name‘)
    for i in res:
        print(i.name)

    res = models.Product.objects.filter(id=1).first()
    print(res.gender)
    print(res.get_gender_display())  # 获取编号对应的中文注释
    models.Product.objects.create(...gender=1)