QuerySet数据类型:
1、可切片,可迭代 [obj,....]
2、惰性查询:
articles_list=models.Article.objects.all()
使用articles_list,比如if articles_list,这时转换sql语句
3、缓存机制
articles_list=models.Article.objects.all()
for i in articles_list:
print(i.title) # hit the database
for i in articles_list:
print(i.title) # not hit the database
==============================================
for i in models.Article.objects.all():
print(i.title) # hit the database
for i in models.Article.objects.all():
print(i.title) # hit the database
4、优化查询
articles_list=models.Article.objects.all().iterator()
for i in articles_list:
print(i.title) # hit the database
for i in articles_list:
print(i.title) # 无结果
连表操作:
表关系:
class UserInfo(AbstractUser): # settings: AUTH_USER_MODEL = "blog.UserInfo"
"""
用户信息
"""
nid = models.BigAutoField(primary_key=True)
nickname = models.CharField(verbose_name='昵称', max_length=32,null=True)
telephone = models.CharField(max_length=11, blank=True, null=True, unique=True, verbose_name='手机号码')
avatar = models.FileField(verbose_name='头像', upload_to='avatar', default="avatar/default.png")
create_time = models.DateTimeField(verbose_name='创建时间', auto_now_add=True)
class Blog(models.Model):
"""
站点信息
"""
nid = models.BigAutoField(primary_key=True)
title = models.CharField(verbose_name='个人博客标题', max_length=64)
site = models.CharField(verbose_name='个人博客后缀', max_length=32, unique=True)
theme = models.CharField(verbose_name='博客主题', max_length=32)
user = models.OneToOneField(to='UserInfo', to_field='nid')
class Category(models.Model):
nid = models.AutoField(primary_key=True)
title = models.CharField(verbose_name='分类标题', max_length=32)
blog = models.ForeignKey(verbose_name='所属博客', to='Blog', to_field='nid')
class Article(models.Model):
nid = models.BigAutoField(primary_key=True)
title = models.CharField(max_length=50, verbose_name='文章标题')
desc = models.CharField(max_length=255, verbose_name='文章描述')
# category字段: 与Article对象关联的category对象
category = models.ForeignKey(verbose_name='文章类型', to='Category', to_field='nid', null=True)
# user字段:与Article对象关联的user字段
user = models.ForeignKey(verbose_name='所属用户', to='UserInfo', to_field='nid')
tags = models.ManyToManyField(
to="Tag",
through='Article2Tag',
through_fields=('article', 'tag'),
)
class ArticleDetail(models.Model):
nid = models.AutoField(primary_key=True)
content = models.TextField(verbose_name='文章内容', )
article = models.OneToOneField(verbose_name='所属文章', to='Article', to_field='nid')
class Article2Tag(models.Model):
nid = models.AutoField(primary_key=True)
article = models.ForeignKey(verbose_name='文章', to="Article", to_field='nid')
tag = models.ForeignKey(verbose_name='标签', to="Tag", to_field='nid')
class Tag(models.Model):
nid = models.AutoField(primary_key=True)
title = models.CharField(verbose_name='标签名称', max_length=32)
blog = models.ForeignKey(verbose_name='所属博客', to='Blog', to_field='nid')
关联表的添加记录操作:
1、创建一篇文章对象:
user_obj=models.UserInfo.objects.get(nid=1)
category_obj=models.Category.objects.get(nid=2)
#################一对多关系绑定#########################
# 方式1:
article_obj=models.Article.objects.create(nid=5,title="招呼亚星"....,user=user_obj,category=category_obj)
# 方式2:
article_obj=models.Article.objects.create(nid=5,title="招呼亚星"....,user_id=1,category_id=2)
'''
Article:
nid title user_id category_id
5 招呼亚星 1 2
'''
#################多对多关系绑定#########################
if 没有中介模型:
tags = models.ManyToManyField("Tag")
'''
ORM创建的第三张表:
Article2tags:
nid article_id tag_id
1 5 1
2 5 2
'''
实例:给article_obj绑定kw1,kw2的标签
tag1=Tag.objects.filter(title=kw1).first()
tag2=Tag.objects.filter(title=kw2).first()
article_obj.tags.add(tag1,tag2) #
article_obj.tags.add(*[tag1,tag2])
article_obj.tags.add(1,2)
article_obj.tags.add(*[1,2])
解除关系:
article_obj.tags.remove(tag1,tag2)
article_obj.tags.clear()
重置关系:
article_obj.tags.clear()
article_obj.tags.add(tag1,tag2)
=====
article_obj.tags.set(tag1,tag2)
if 有中介模型:
tags = models.ManyToManyField(
to="Tag",
through='Article2Tag',
through_fields=('article', 'tag'),
)
class Article2Tag(models.Model): # 中介模型
nid = models.AutoField(primary_key=True)
article = models.ForeignKey(verbose_name='文章', to="Article", to_field='nid')
tag = models.ForeignKey(verbose_name='标签', to="Tag", to_field='nid')
绑定多对多的关系,有中介模型,不能再使用article_obj.tags.add(),remove()等方法;
只能用Article2Tag表进行实例对象。
实例:给article_obj绑定kw1,kw2的标签:
models.Article2Tag.objects.create(tag_id=1,article_id=5)
models.Article2Tag.objects.create(tag_id=2,article_id=5)
关联表的查询:
基于对象查询(子查询):
一对多的查询:
实例1:查询主键为4的文章的分类名称(正向查询,按字段)
article_obj=models.Article.objects.get(nid=4)
print(article_obj.category.title)
SELECT * FROM "blog_article" WHERE "blog_article"."nid" = 4; // category_id=2
SELECT * FROM "blog_category" WHERE "blog_category"."nid" = 2;
实例2:查询用户yuan发表过的所有的文章(反向查询,表名_set)
yuan=models.UserInfo.objects.get(username="yuan")
book_list=yuan.article_set.all() # QuerySet
多对多的查询:
实例3:查询主键为4的文章的标签名称(正向查询,按字段)
article_obj=models.Article.objects.get(nid=4)
tag_list=article_obj.tags.all() # 是通过Article2Tag找到tag表中关联的tag记录
for i in tag_list:
print(i.title)
实例4:查询web开发的这个标签对应的所有的文章(反向查询,按表名_set)
tag_obj=models.Tag.objects.get(title="web开发")
article_list=tag_obj.article_set.all()
for i in article_list:
print(i.title)
实例5:查询web开发的这个标签对应的所有的文章对应的作者名字
tag_obj=models.Tag.objects.get(title="web开发")
article_list=tag_obj.article_set.all()
for article in article_list:
print(article.user.username)
基于QuerySet跨表查询 正向查询,按字段 ;反向查询,按表名(join查询)
一对多的查询:
实例1:查询主键为4的文章的分类名称
models.Article.objects.filter(nid=4).values("category__title")
models.Category.objects.filter(article__nid=4).values("title")
实例2:查询用户yuan发表过的所有的文章
models.UserInfo.objects.filter(username="yuan").values(article__title)
models.Article.objects.filter(user__username="yuan").values("title")
多对多的查询:
实例3:查询主键为4的文章的标签名称(正向查询,按字段)
models.Article.objects.filter(nid=4).values("tags__title")
models.Tag.objects.filter(article__nid=4).values("title")
实例4:查询web开发的这个标签对应的所有的文章(反向查询,按表名_set)
models.Article.objects.filter(tags__title="web开发").values("title")
models.Tag.objects.filter(title="web开发").values("article__title")
实例5:查询web开发的这个标签对应的所有的文章对应的作者名字
models.Tag.objects.filter(title="web开发").values("article__user__username")
models.UserInfo.objects.filter(article__tags__title="web开发").values("username")
聚合查询与分组查询:
聚合查询:
# 查询所有书籍的平均价格
Book.objects.all().aggregate(Avg('price'))
分组查询:
#查询每一个出版社出版过的名字以及出版书籍个数
sql: select publish.name,Count(book.name) from Book inner join publish on book.pub_id=publish.id
group by publish.name
ORM: models.Publish.objects.all().annotate(c=Count("book_id")).values("name","c")