python之Django学习笔记（四）---数据模型（SQLITE3）以及相关操作

数据模型在djangoTestApp/models.py文件中定义表和表结构，之前已经定义了一个Student表，如下：

from django.db import models

SEX_CHOICE = (
    ('F','Female'),
    ('M','male')
)
# Create your models here.
class Student(models.Model):
    No = models.CharField('学号',max_length = 10)
    Name = models.CharField('姓名',max_length = 20)
    Sex = models.CharField('性别',max_length = 1,choices = SEX_CHOICE,default = 'M')
    Age = models.IntegerField('年龄')

字段类型主要有以下几种：

CharField：字符型

IntergerField：整型

DateField：日期型

DateTimeField：日期时间型

FloatField：浮点型

BooleanField：布尔型

BigIntergerField：大数据型

FileField：文件类型

...

当然类型也可以自定义

数据表创建好后在命令行中使用如下语句写入数据库：

python manage.py makemigrations
python manage.py migrate

命令行中输入如下命令可以进入数据库操作界面：

D:\PycharmProjects\untitled\MyTestProject\djangoTestPro>python manage.py shell
>>> from djangoTestApp import models

一、增加操作

在django中增加有如下4种方式：

1、直接使用create增加

>>>models.Student.objects.create(No='19001',Name='watertaro',Sex='M',Age=30)

2、先创建一个对象再保存

>>>p = models.Student(No='19002',Name='Mark',Sex='F',Age=27)
>>>p.save

3、先创建一个对象，给对象的参数赋值后再保存

>>> p = models.Student()
>>> p.No='19005'
>>> p.Name='WangWU'
>>> p.Sex='M'
>>> p.Age=35
>>> p.save()

4、查看和增加，不存在则增加，存在则查询

>>> models.Student.objects.get_or_create(No='19006',Name='LiLiu',Sex='F',Age=21)

(<Student: No:19006;Name:LiLiu;Sex:F;Age:21>, True)

返回一个元祖，第一个表示对象，第二个参数True表示新增，False表示查询

再次执行上述命令则返回的第二个参数为False（已经执行过一次，表示已经存在数据了）

二、查询操作

get()方法：

>>> models.Student.objects.get(No='19003')
<Student: Student object (5)>

这里只显示查到了数据，可以使用__dict__（这里是俩个下划线）来查看（返回的是一个字典）

>>> models.Student.objects.get(No='19002').__dict__
{'_state': <django.db.models.base.ModelState object at 0x00000000041AD940>, 'id: 4, 'No': '19002', 'Name': 'Mark', 'Sex': 'F', 'Age': 27}
>>> s = models.Student.objects.get(No='19002')
>>> s.__dict__
{'_state': <django.db.models.base.ModelState object at 0x00000000041AD438>, 'id: 4, 'No': '19002', 'Name': 'Mark', 'Sex': 'F', 'Age': 27}

也可以在数据模型的类（即Student类）中增加一个__str__的返回值：

    def __str__(self):
        return 'No:' + self.No + ';Name:' + self.Name + ';Sex:' + self.Sex + ';Age:' + str(self.Age)

使用exit()退出shell再重新进入，再次查询如下：

>>> models.Student.objects.get(No='19003')
<Student: No:19003;Name:ZhangSan;Sex:F;Age:30>

get()方法只能查询到有且只有一条数据的对象，如果没有查询到或者查询结果不止一条会报错，后面会讲到可以查询N条数据方法（filter）

all()方法

可以查询表中所有数据，如下：

>>> models.Student.objects.all()
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student:No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19006;Name:LiLiu;Sex:F;Age:21>]>

若只是查询前2条数据，可以使用类似列表中切片方法来查询（这里切片不支持负数）

>>> models.Student.objects.all()[:2]
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19002;Name:Mark;Sex:F;Age:27>]>

如果只需要显示Name，可以按照如下操作：

>>> t = models.Student.objects.all()
>>> item = models.Student.objects.all()
>>> for i in item:
...     print(i.Name)
...
watertaro
Mark
ZhangSan
LiSi
WangWU

filter()方法：

filter可以查询出多条或者空数据，这也是查询中使用最多的方法，下面介绍使用方法

1、精确查询（__exact）和不区分大小写的精确查询（__iexact）

>>> models.Student.objects.filter(No='190')#查询为空
<QuerySet []>
>>> models.Student.objects.filter(No='19001')#查询到一条数据
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>]>
>>> models.Student.objects.filter(Age=30)#查询到多条数据
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>]>

也可以使用No__exact（双下划线）来精确查询和直接查询的效果是一样的，如下：

>>> models.Student.objects.filter(No__exact='190')#查询为空
<QuerySet []>
>>> models.Student.objects.filter(No__exact='19001')#查询到一条数据
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>]>
>>> models.Student.objects.filter(Age__exact=30)#查询到多条数据
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>]>

之前Name中有watertaro，增加一个WaterTaro这个Name：

>>> models.Student.objects.create(No='19007',Name='WaterTaro',Sex='F',Age=29)
<Student: No:19007;Name:WaterTaro;Sex:F;Age:29>

这时使用如下查询语句可以看到后一个查询语句不区分大小写，但是精确匹配的：

>>> models.Student.objects.filter(Name='WaterTaro')
<QuerySet [<Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>
>>> models.Student.objects.filter(Name__exact='WaterTaro')
<QuerySet [<Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>
>>> models.Student.objects.filter(Name__iexact='WaterTaro')
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>

3、包含某个字段的查询（__contains和__icontains）

>>> models.Student.objects.filter(Name__contains='watertaro')
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>
>>> models.Student.objects.filter(Name__icontains='watertaro')
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>

老版本中__contains是区分大小写的，最新django不区分

4、正则表达式查询（__regex）和不分区大小写的正则表达式查询（__iregex）

我们增加一个Name为LuTao的同学：

>>> models.Student.objects.create(No='19008',Name='LuTao',Sex='F',Age=25)
<Student: No:19008;LuTao;Sex:F;Age:25>

此时查询以u结尾的名字

>>> models.Student.objects.filter(Name__regex='u$')
<QuerySet [<Student: No:19006;Name:LiLiu;Sex:F;Age:21>]>

只能查到LiLiu，其实包含u和U的名字还有LuTao和WangWU，如果使用下面的语句，则可以查到LiLiu和WangWU

>>> models.Student.objects.filter(Name__iregex='u$')
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19006;Name:LiLiu;Sex:F;Age:21>]>

5、大于（gt）、大于等于（gte）、小于（lt）、小于等于（lte）

看下面查询的例子：

>>> models.Student.objects.filter(Age__gt=30)#查询Age大于30
<QuerySet [<Student:No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> models.Student.objects.filter(Age__gte=30)#查询Age大于等于30
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> models.Student.objects.filter(Age__lt=29)#查询Age小于29
<QuerySet [<Student: No:19002;Name:Mark;Sex:F;Age:27>]>
>>> models.Student.objects.filter(Age__lte=29) #查询Age小于等于29
<QuerySet [<Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>

6、以某字段开始（startswith）、以某字段结束（endswith）

>>> models.Student.objects.filter(Name__startswith='wa')#以wa开始的Name（不区分大小写）
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>
>>> models.Student.objects.filter(Name__endswith='n')#以n结尾的Name（不区分大小写）
<QuerySet [<Student: No:19003;Name:ZhangSan;Sex:F;Age:30>]>

7、与（&）、或（|）

>>> models.Student.objects.filter(Age=30) & models.Student.objects.filter(Sex='F')#查询Age=30并且Sex为F
<QuerySet [<Student: No:19003;Name:ZhangSan;Sex:F;Age:30>]>
>>> from django.db.models import Q
>>> models.Student.objects.filter(Q(Age=30) & Q(Sex='F'))#等同于上面查询
<QuerySet [<Student: No:19003;Name:ZhangSan;Sex:F;Age:30>]>
>>> models.Student.objects.filter(Age=30) | models.Student.objects.filter(Age=35)#查询Age为30或者35
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> models.Student.objects.filter(Q(Age=30)|Q(Age=35))#等同于上面查询
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>]>

8、查询集中的第一条数据（first()）、查询集中的最后一条数据（last()）

>>> models.Student.objects.all()#查询所有
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student:No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>
>>> models.Student.objects.all().first()#获取第一条数据
<Student: No:19001;Name:watertaro;Sex:M;Age:30>
>>> models.Student.objects.all().last()#获取最后一条数据
<Student: No:19007;Name:WaterTaro;Sex:F;Age:29>

exclude()方法：

exclude是排除方法，即查询到的是排除给出的条件，比如我们要查询不带u的Name

>>> models.Student.objects.exclude(Name__contains='u')
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>

查询结果中确实少了带u的3个同学：LuTao,LiLiu,WangWU

方法之间也可以连起来用，比如查询带u或U的名字但Age不为21的同学：

>>> models.Student.objects.filter(Name__contains='u').exclude(Age=21)
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19008;Name:LuTao;Sex:F;Age:25>]>

结果中少了Age=21的LiLiu同学

count()方法：

查询结果的条数

>>> models.Student.objects.all().count()
8
>>> models.Student.objects.exclude(Name__regex='u$').count()
7
>>> models.Student.objects.exclude(Name__iregex='u$').count()
6

因为查询结果是一个QuerySet集，是可以迭代的，所以条数也可以使用下面方法，但不建议使用：

>>> len(models.Student.objects.all())
8
>>> len(models.Student.objects.exclude(Name__regex='u$'))
7
>>> len(models.Student.objects.exclude(Name__iregex='u$'))
6

reverse()方法：

前面说了数据库查询结果切片不支持负索引，那如果要查询最后一条数据就要用到reverser()方法了：

>>> models.Student.objects.all().order_by('Age')#根据Age排序
<QuerySet [<Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>, <Student: No
:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> models.Student.objects.all().order_by('Age').reverse()#reverse()类似order_by('-Age')
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Stude
nt: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>, <Student: No:19002;Name:Mark;Sex:F;Age:27>]>
>>> models.Student.objects.all().order_by('Age').reverse()[0]#查询最后一条数据
<Student: No:19005;Name:WangWU;Sex:M;Age:35>
>>> models.Student.objects.all().order_by('Age').reverse()[:1]#查询最后一条数据
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> models.Student.objects.all().order_by('Age').reverse()[:2]#查询最后俩条数据
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19001;Name:watertaro;Sex:M;Age:30>]>
>>> models.Student.objects.all().order_by('Age').reverse()[1]#查询倒数第二条数据
<Student: No:19001;Name:watertaro;Sex:M;Age:30>

query方法：

在每个执行语句中加一个.query即可查询，如下所示：

>>> print(str(models.Student.objects.all().query))#查看
SELECT "djangoTestApp_student"."id", "djangoTestApp_student"."No", "djangoTestApp_student"."Name", "djangoTestApp_student"."Sex", "djangoTestApp_student"."Age" FROM "djangoTestApp_student"
>>> print(str(models.Student.objects.filter(Q(Age=30)&Q(Sex='F')).query))#查看
SELECT "djangoTestApp_student"."id", "djangoTestApp_student"."No", "djangoTestApp_student"."Name", "djangoTestApp_student"."Sex", "djangoTestApp_student"."Age" FROM "djangoTestApp_student" WHERE ("djangoTestApp_student"."Age" = 30 AND "djangoTestApp_student"."Sex" = F)

values方法和values_list方法：

values方法返回的是dict类型数据，values_list返回的是元祖型数据，如下所示

>>> models.Student.objects.values('No')
<QuerySet [{'No': '19001'}, {'No': '19002'}, {'No': '19003'}, {'No': '19004'}, {'No': '19005'}, {'No': '19007'}]>
>>> models.Student.objects.values_list('No')
<QuerySet [('19001',), ('19002',), ('19003',), ('19004',), ('19005',), ('19007',)]>
>>> models.Student.objects.values_list('No',flat=True)#使用flat直接显示单个字段，不需要元祖
<QuerySet ['19001', '19002', '19003', '19004', '19005', '19007']>

defer()方法

defer是不去查询某字段，如查询Student表，但不查询Age这个字段的值

>>> models.Student.objects.all().defer('Age').query.__str__()
'SELECT "djangoTestApp_student"."id", "djangoTestApp_student"."No", "djangoTestApp_student"."Name", "djangoTestApp_student"."Sex" FROM "djangoTestApp_student"'

可以查询类SQL语句中并没有查询Age这个字段

only()方法：

只查询某字段，如Student表中，只查询Name这个字段

>>> models.Student.objects.all().only('Name').query.__str__()
'SELECT "djangoTestApp_student"."id", "djangoTestApp_student"."Name" FROM "djangoTestApp_student"'

三、更新操作：

更新有俩种方法如下

>>> models.Student.objects.filter(Name__contains='u')
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19006;Name:LiLiu;Sex:F;Age:21>, <Student: No:19008;Name:LuTao;Sex:F;Age:25>]>
>>> models.Student.objects.filter(Name__contains='u').update(Age=100)
3
>>> models.Student.objects.filter(Name__contains='u')
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:100>, <Student: No:19006;Name:LiLiu;Sex:F;Age:100>, <Student: No:19008;Name:LuTao;Sex:F;Age:100>]>

update之后返回的是更新的数据个数，这个适合多条数据的更新

>>> t = models.Student.objects.get(Name='WangWU')
>>> t
<Student: No:19005;Name:WangWU;Sex:M;Age:100>
>>> t.Sex='F'
>>> t.Age=35
>>> t
<Student: No:19005;Name:WangWU;Sex:F;Age:35>
>>> t.save()
>>> t
<Student: No:19005;Name:WangWU;Sex:F;Age:35>

上面这种方式是查询出一条数据，然后对其对象进行修改，最后一定记得要保存

四、删除操作：

删除关键字delete()，如下使用

>>> models.Student.objects.filter(Name__iexact='lutao')
<QuerySet [<Student: No:19008;Name:LuTao;Sex:F;Age:25>]>
>>> models.Student.objects.filter(Name__iexact='lutao').delete()
(1, {'djangoTestApp.Student': 1})
>>> models.Student.objects.filter(Name__iexact='lutao')
<QuerySet []>

或者如下先查询，再删除

>>> s = models.Student.objects.filter(Name__iexact='liliu')
>>> s
<QuerySet [<Student: No:19006;Name:LiLiu;Sex:F;Age:21>]>
>>> s.delete()
(1, {'djangoTestApp.Student': 1})
>>> s
<QuerySet []>

五、排序操作：

和oracle一样关键字为order_by()

>>> models.Student.objects.all().order_by('Name')
<QuerySet [<Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19
007;Name:WaterTaro;Sex:F;Age:29>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19001;Name:watertaro;Sex:M;Age:30>]>
>>> models.Student.objects.all().order_by('-Name')
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>, <St
udent: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>]>

字段前面加连接符（-）标识倒序查询

六、去重操作：

去重关键字distinct()

当前django版本在shell中使用|合并时已经进行了去重操作，所以这个关键字暂时用不着

>>> a = models.Student.objects.filter(Name__contains='u')
>>> b = models.Student.objects.filter(Age=29)
>>> c = models.Student.objects.filter(Sex='M')
>>> a
<QuerySet [<Student: No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> b
<QuerySet [<Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19007;Name:W
aterTaro;Sex:F;Age:29>]>
>>> c
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>]>
>>> abc = a | b |c
>>> abc
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student:No:19007;Name:WaterTaro;Sex:F;Age:29>]>

如上a、b、c中是有重复的，但合并为abc之后并没有看到重复项

七、起别名

和SQL类型，我们也可以使用as给每个字段起别名

>>> t = models.Student.objects.all().extra(select={'MyName':'Name'})#把字段Name起个名MyName
>>> t
<QuerySet [<Student: No:19001;Name:watertaro;Sex:M;Age:30>, <Student: No:19002;Name:Mark;Sex:F;Age:27>, <Student: No:19003;Name:ZhangSan;Sex:F;Age:30>, <Student
: No:19004;Name:LiSi;Sex:M;Age:29>, <Student: No:19005;Name:WangWU;Sex:M;Age:35>, <Student: No:19007;Name:WaterTaro;Sex:F;Age:29>]>
>>> t[0].Name
'watertaro'
>>> t[0].MyName#和Name一样
'watertaro'
>>> models.Student.objects.all().extra(select={'MyName':'Name'}).query.__str__()#查询类似SQL的语句
'SELECT (Name) AS "MyName", "djangoTestApp_student"."id", "djangoTestApp_student"."No", "djangoTestApp_student"."Name", "djangoTestApp_student"."Sex", "djangoTestApp_student"."Age" FROM "djangoTestApp_student"'

八、聚合计算

在models.py中增加一张分数表Score，用于聚合计算

class Score(models.Model):
    No = models.CharField('学号', max_length=10)
    Name = models.CharField('姓名', max_length=20)
    Course = models.CharField('学科',max_length = 10)
    Score = models.IntegerField('成绩',default = 0)

    def __str__(self):
        return 'No:' + self.No + ';Name:' + self.Name + ';Course:' + self.Course + ';Score:' + str(self.Score)

在命令行中执行如下语句

D:\PycharmProjects\untitled\MyTestProject\djangoTestPro>python manage.py makemigrations
D:\PycharmProjects\untitled\MyTestProject\djangoTestPro>python manage.py migrate

进入python shell增加数据如下：

D:\PycharmProjects\untitled\MyTestProject\djangoTestPro>python manage.py shell
>>> from djangoTestApp import models
>>> models.Score.objects.create(No='19001',Name='watertaro',Course='Chinese',Score=56)
<Score: No:19001;Name:watertaro;Course:Chinese;Score:56>
>>> models.Score.objects.create(No='19002',Name='Mark',Course='Chinese',Score=70)
<Score: No:19002;Name:Mark;Course:Chinese;Score:70>
>>> models.Score.objects.create(No='19003',Name='ZhangSan',Course='Chinese',Score=68)
<Score: No:19003;Name:ZhangSan;Course:Chinese;Score:68>
>>> models.Score.objects.create(No='19004',Name='LiSi',Course='Chinese',Score=91)
<Score: No:19004;Name:LiSi;Course:Chinese;Score:91>
>>> models.Score.objects.create(No='19005',Name='WangWU',Course='Chinese',Score=82)
<Score: No:19005;Name:WangWU;Course:Chinese;Score:82>
>>> models.Score.objects.create(No='19007',Name='WaterTaro',Course='Chinese',Score=66)
<Score: No:19007;Name:WaterTaro;Course:Chinese;Score:66>
>>> models.Score.objects.create(No='19001',Name='watertaro',Course='Math',Score=78)
<Score: No:19001;Name:watertaro;Course:Math;Score:78>
>>> models.Score.objects.create(No='19002',Name='Mark',Course='Math',Score=81)
<Score: No:19002;Name:Mark;Course:Math;Score:81>
>>> models.Score.objects.create(No='19003',Name='ZhangSan',Course='Math',Score=66)
<Score: No:19003;Name:ZhangSan;Course:Math;Score:66>
>>> models.Score.objects.create(No='19004',Name='LiSi',Course='Math',Score=80)
<Score: No:19004;Name:LiSi;Course:Math;Score:80>
>>> models.Score.objects.create(No='19005',Name='WangWU',Course='Math',Score=55)

<Score: No:19005;Name:WangWU;Course:Math;Score:55>
>>> models.Score.objects.create(No='19007',Name='WaterTaro',Course='Math',Score=78)
<Score: No:19007;Name:WaterTaro;Course:Math;Score:78>
>>> models.Score.objects.create(No='19001',Name='watertaro',Course='English',Score=70)
<Score: No:19001;Name:watertaro;Course:English;Score:70>
>>> models.Score.objects.create(No='19002',Name='Mark',Course='English',Score=51)
<Score: No:19002;Name:Mark;Course:English;Score:51>
>>> models.Score.objects.create(No='19003',Name='ZhangSan',Course='English',Score=59)
<Score: No:19003;Name:ZhangSan;Course:English;Score:59>
>>> models.Score.objects.create(No='19004',Name='LiSi',Course='English',Score=90
)
<Score: No:19004;Name:LiSi;Course:English;Score:90>
>>> models.Score.objects.create(No='19005',Name='WangWU',Course='English',Score=73)
<Score: No:19005;Name:WangWU;Course:English;Score:73>
>>> models.Score.objects.create(No='19007',Name='WaterTaro',Course='English',Score=60)
<Score: No:19007;Name:WaterTaro;Course:English;Score:60>
>>> models.Score.objects.all()
<QuerySet [<Score: No:19001;Name:watertaro;Course:Chinese;Score:56>, <Score: No:19002;Name:Mark;Course:Chinese;Score:70>, <Score: No:19003;Name:ZhangSan;Course:Chinese;Score:68>, <Score: No:19004;Name:LiSi;Course:Chinese;Score:91>, <Score:No:19005;Name:WangWU;Course:Chinese;Score:82>, <Score: No:19007;Name:WaterTaro;Course:Chinese;Score:66>, <Score: No:19001;Name:watertaro;Course:Math;Score:78>,<Score: No:19002;Name:Mark;Course:Math;Score:81>, <Score: No:19003;Name:ZhangSan;Course:Math;Score:66>, <Score: No:19004;Name:LiSi;Course:Math;Score:80>, <Score: No:19005;Name:WangWU;Course:Math;Score:55>, <Score: No:19007;Name:WaterTaro;Course:Math;Score:78>, <Score: No:19001;Name:watertaro;Course:English;Score:70>, <Score: No:19002;Name:Mark;Course:English;Score:51>, <Score: No:19003;Name:ZhangSan;Course:English;Score:59>, <Score: No:19004;Name:LiSi;Course:English;Score:90>, <Score: No:19005;Name:WangWU;Course:English;Score:73>, <Score: No:19007;Name:WaterTaro;Course:English;Score:60>]>

1、聚合计数：类似SQL中的group by字段，如下求各年龄的人数

>>> from django.db.models import Count
>>> models.Student.objects.values('Age').annotate(cnt=Count('Age')).values('Age','cnt')#以Age为分组，查询每个Age有几个人
<QuerySet [{'Age': 27, 'cnt': 1}, {'Age': 29, 'cnt': 2}, {'Age': 30, 'cnt': 2},{'Age': 35, 'cnt': 1}]>

使用query可以看到具体释义

>>> models.Student.objects.values('Age').annotate(cnt=Count('Age')).values('Age','cnt').query.__str__()
'SELECT "djangoTestApp_student"."Age", COUNT("djangoTestApp_student"."Age") AS "cnt" FROM "djangoTestApp_student" GROUP BY "djangoTestApp_student"."Age"'

这里的Count是对查询出的Age条数进行统计，不一定为Age。cnt即为

2、聚合求和：类似SQL中的sum字段，如下求所有同学的所有课程的总分

>>> from django.db.models import Sum #导入Sum
>>> models.Score.objects.values('No','Name').annotate(sum_score=Sum('Score')).values('No','Name','sum_score')#查询同学的总分
<QuerySet [{'No': '19001', 'Name': 'watertaro', 'sum_score': 204}, {'No': '19002', 'Name': 'Mark', 'sum_score': 202}, {'No': '19003', 'Name': 'ZhangSan', 'sum_score': 193}, {'No': '19004', 'Name': 'LiSi', 'sum_score': 261}, {'No': '19005','Name': 'WangWU', 'sum_score': 210}, {'No': '19007', 'Name': 'WaterTaro', 'sum_score': 204}]>

结合前面的排序，以总分从高到低排序如下

>>> models.Score.objects.values('No','Name').annotate(sum_score=Sum('Score')).values('No','Name','sum_score').order_by('-sum_score')
<QuerySet [{'No': '19004', 'Name': 'LiSi', 'sum_score': 261}, {'No': '19005', 'Name': 'WangWU', 'sum_score': 210}, {'No': '19001', 'Name': 'watertaro', 'sum_score': 204}, {'No': '19007', 'Name': 'WaterTaro', 'sum_score': 204}, {'No': '19002', 'Name': 'Mark', 'sum_score': 202}, {'No': '19003', 'Name': 'ZhangSan', 'sum_score': 193}]>

3、聚合求平均数：类似SQL中的avg字段，如下求每门课程的平均分

>>> from django.db.models import Avg #导入Avg
>>> models.Score.objects.values('Course').annotate(avg_course=Avg('Score')).values('Course','avg_course')
<QuerySet [{'Course': 'Chinese', 'avg_course': 72.16666666666667}, {'Course': 'English', 'avg_course': 67.16666666666667}, {'Course': 'Math', 'avg_course': 73.0}]>
>>> models.Score.objects.values('Course').annotate(avg_course=Avg('Score')).values('Course','avg_course').query.__str__()
'SELECT "djangoTestApp_score"."Course", AVG("djangoTestApp_score"."Score") AS "avg_course" FROM "djangoTestApp_score" GROUP BY "djangoTestApp_score"."Course"'

从上可以看到各门课程的平均值，查看执行的类SQL语句，意思都差不多，只是写法稍微不同

4、聚合求最小值：类似SQL中的min字段，如下求每门课程的最低分数

>>> from django.db.models import Min#导入Min
>>> models.Score.objects.values('Course').annotate(min_course=Min('Score')).values('Course','min_course')
<QuerySet [{'Course': 'Chinese', 'min_course': 56}, {'Course': 'English', 'min_course': 51}, {'Course': 'Math', 'min_course': 55}]>

5、聚合求最大值：类似SQL中的max字段，如下求每门课程的最高分数

>>> from django.db.models import Max#导入Max
>>> models.Score.objects.values('Course').annotate(min_course=Max('Score')).values('Course','min_course')
<QuerySet [{'Course': 'Chinese', 'min_course': 91}, {'Course': 'English', 'min_course': 90}, {'Course': 'Math', 'min_course': 81}]>

九、字段聚合显示

比如Student表中，如果想把姓名（Name）和学号（No）合并显示为Name(No)，比如No=19001显示为watertaro(19001)，可以如下操作

1、在Student表类中增加如下代码

class Student(models.Model):
    No = models.CharField('学号',max_length = 10)
    Name = models.CharField('姓名',max_length = 20)
    Sex = models.CharField('性别',max_length = 1,choices = SEX_CHOICE,default = 'M')
    Age = models.IntegerField('年龄')

    def name_no(self):
        return self.Name + '(' + self.No + ')'
    name_no.short_description = '姓名(学号)'
    NameNo = property(name_no)

2、在admin.py中修改显示字段

class StudentAdmin(admin.ModelAdmin):
    list_display = ('NameNo','Sex','Age',)

此时刷新界面就会显示如下样式：

完结！

python之Django学习笔记（四）---数据模型（SQLITE3）以及相关操作

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