django之多表查询操作

Posted 2020-11-15 -777

基于双下划线的跨表查询（连表查询 join）

    select emp.name from emp inner join dep on emp.dep_id = dep.id where dep.name='技术';
    select emp.name from dep inner join emp on emp.dep_id = dep.id where dep.name='技术';

示例:

# 一对一
# 查询一下王洋的电话号码

# ret = models.Author.objects.filter(name='王洋').values('au__telephone')

# ret = models.AuthorDetail.objects.filter(author__name='王洋').values('telephone')
# print(ret) #<QuerySet [{'au__telephone': '110'}]> #<QuerySet [{'telephone': '110'}]>
#

# 一对多
# 海狗的怂逼人生这本书是哪个出版社出版的
# ret = models.Book.objects.filter(title='海狗的怂逼人生').values('publishs__name')
# print(ret) #<QuerySet [{'publishs__name': '24期出版社'}]>
# ret = models.Publish.objects.filter(book__title='海狗的怂逼人生').values('name')
# print(ret) #<QuerySet [{'name': '24期出版社'}]>


#查询一下24期出版社出版了哪些书
# ret = models.Publish.objects.filter(name='24期出版社').values('book__title')
# print(ret) #<QuerySet [{'book__title': '华丽的产后护理'}, {'book__title': '海狗的怂逼人生'}]>

# ret = models.Book.objects.filter(publishs__name='24期出版社').values('title')
# print(ret) #<QuerySet [{'title': '华丽的产后护理'}, {'title': '海狗的怂逼人生'}]>

# 多对多
#海狗的怂逼人生 是哪些作者写的
# ret = models.Book.objects.filter(title='海狗的怂逼人生').values('authors__name')
# print(ret)

# ret = models.Author.objects.filter(book__title='海狗的怂逼人生').values('name')
# print(ret) #<QuerySet [{'name': '王洋'}, {'name': '海狗'}]>
# return render(request,'index.txt',{'x':123,'y':456})


# related_name
# 查询一下24期出版社出版了哪些书
ret = models.Publish.objects.filter(name='24期出版社').values('xxx__title') #xxx代替反向查询的小写表名
print(ret)

聚合查询

ret = models.Book.objects.all().aggregate(a=Avg('price'),m=Max('price'))
print(ret) 
#{'price__avg': 45.1, 'price__max': Decimal('200.00')} python字典格式,也就是说,聚合查询是orm语句的结束

分组查询

    # 每个出版社出版的书的平均价格
    # 用的是publish表的id字段进行分组
    # ret = models.Book.objects.values('publishs__id').annotate(a=Avg('price'))
    # 用的book表的publishs_id字段进行分组
    # ret = models.Book.objects.values('publishs_id').annotate(a=Avg('price'))
    # print(ret)
    # ret = models.Publish.objects.annotate(a=Avg('book__price')).values('a')
    # print(ret) #<QuerySet [{'a': None}, {'a': 71.166667}, {'a': 6.0}]>

F查询

from django.db.models import Avg, Sum, Max, Min, Count,F
查询一下评论数大于点赞数的书
# ret = models.Book.objects.filter(comment__gt=F('good'))
# print(ret)


将所有书的价格上调100块
# models.Book.objects.all().update(
#     price=F('price')+100
# )

Q查询

    from django.db.models import Avg, Sum, Max, Min, Count, F,Q
    ret = models.Book.objects.filter(Q(id=2)&Q(Q(price__gt=112)|~Q(comment__lte=200)))
    print(ret)