Django models(day 7)
查询集：
在管理器上调用过滤器方法返下回查询集
查询集经过过滤器后返回的查询集
惰性执行：创建查询集不会带来任何数据的访问，直到调用数据时，才会访问数据
直接访问数据的情况：迭代、序列化、j与if语句合用
返回查询集的方法称为过滤器
返回符合条件的数据:
all()
>>> from myapp.models import Students,Grades
>>> Grades.objects.all()
filter(key=values)
>>> Grades.objects.filter(pk=1)
过滤掉符合条件的数据：exclude
order_by
values():一条数据就是一个对象（字典）
>>> Grades.objects.values()
>>>Grades.objects.get()
count() 返回查询对象的个数
>>> Grades.objects.count()
4
first()
>>> Grades.objects.first()
last()
>>> Grades.objects.last()
exists()
>>> Grades.objects.exists()
True
判断查询集中是否有数据
>>> Grades.objects.count()
4
>>> Grades.objects.exists()
True
二、限制查询集
# 显示前五条学生 def stu2 (request): stulist=Students.stu_objects.all()[0:5] return render(request,'myapp/students.html', {"students":stulist})
url(r'^stu2/$',views.stu2),
# 分页显示 # 0-5 5-10 10-15 # 1 2 3 def stupage(request, page): page=int(page) stulist=Students.stu_objects.all()[(page-1)*5:page*5] return render(request,'myapp/students.html', {"students":stulist})
url('^stu/(\d+)$',views.stupage)
查询集的缓冲，在新建的查询集中，缓冲首次为空，第一次对查询集球值，会发生数据缓冲
字段查询：属性名称_比较运算符=值 转义：
外键查询：属性名_id
比较运算符：exact判断 contains是否包含
def stusearch(request): # stulist=Students.stu_objects.filter(sname__contains='bob') # stulist=Students.stu_objects.filter(sname__startswith='b') # stulist = Students.stu_objects.filter(sname__endswith='b') # stulist = Students.stu_objects.filter(pk__in=[2,4,6,8]) # stulist = Students.stu_objects.filter(sage__gt=30) # stulist = Students.stu_objects.filter(sage__lte=15) stulist = Students.stu_objects.filter(lasttime__year=2018)
def stusearch(request): stulist=Students.stu_objects.filter(sname__contains='bob') return render(request,'myapp/students.html', {"students":stulist})
聚合函数：
使用 asggregate() 函数返回聚合函数的值：Avo MIN Sum Count Max
from django.db.models import Max,Min def stusearch(request): # stulist=Students.stu_objects.filter(sname__contains='bob') # stulist=Students.stu_objects.filter(sname__startswith='b') # stulist = Students.stu_objects.filter(sname__endswith='b') # stulist = Students.stu_objects.filter(pk__in=[2,4,6,8]) # stulist = Students.stu_objects.filter(sage__gt=30) # stulist = Students.stu_objects.filter(sage__lte=15) # stulist = Students.stu_objects.filter(lasttime__year=2018) stulist=Students.stu_objects.filter(sname__contains='J') maxage=Students.stu_objects.aggregate(Max('sage')) print(maxage) return render(request,'myapp/students.html', {"students":stulist}){'sage__max': 50}
F对象：比较同一个对象下不同的属性：例如找出girlnum>boynum的班级
# F对象：比较同一个对象下不同的属性：例如找出girlnum>boynum的班级 from django.db.models import F,Q def grades_comparison(request): g=Grades.objects.filter(ggirlnum__gt=F('gboynum')) print(g) return HttpResponse("yes")
# 或的关系 # stulist = Students.stu_objects.filter(Q(pk__lt=15)|Q(sage__lt=25)) stulist = Students.stu_objects.filter(~Q(pk__lt=15))
关联查询：带有bob学生描述的学生数据是属于哪个班级的：对象名小写__属性__
# 关联查询：带有bob学生描述的数据是属于哪个班级的：对象名小写__属性 grade=Grades.objects.filter(Students__scontend__contains="bob") print(grade)
from django.shortcuts import render # Create your views here. from django.http import HttpResponse def index(request): return HttpResponse("I love China") from django.shortcuts import render from . models import Grades # Create your views here. from django.http import HttpResponse def index(request): return HttpResponse("I love China") def grades(request): # 去models里取数据 gradeslist=Grades.objects.all() # 将数据传输给模板模板在渲染页面，再将渲染好的页面返回浏览器 return render(request,'myapp/grades.html', {"grades":gradeslist}) from .models import Students def stu (request): stulist=Students.stu_objects.all() return render(request,'myapp/students.html', {"students":stulist}) # 显示前五条学生 def stu2 (request): stulist=Students.stu_objects.all()[0:5] return render(request,'myapp/students.html', {"students":stulist}) # 分页显示 # 0-5 5-10 10-15 # 1 2 3 def stupage(request, page): page=int(page) stulist=Students.stu_objects.all()[(page-1)*5:page*5] return render(request,'myapp/students.html', {"students":stulist}) from django.db.models import Max,Min def stusearch(request): # stulist=Students.stu_objects.filter(sname__contains='bob') # stulist=Students.stu_objects.filter(sname__startswith='b') # stulist = Students.stu_objects.filter(sname__endswith='b') # stulist = Students.stu_objects.filter(pk__in=[2,4,6,8]) # stulist = Students.stu_objects.filter(sage__gt=30) # stulist = Students.stu_objects.filter(sage__lte=15) # stulist = Students.stu_objects.filter(lasttime__year=2018) # stulist=Students.stu_objects.filter(sname__contains='J') # 或的关系 # stulist = Students.stu_objects.filter(Q(pk__lt=15)|Q(sage__lt=25)) stulist = Students.stu_objects.filter(~Q(pk__lt=15)) maxage=Students.stu_objects.aggregate(Max('sage')) print(maxage) # 关联查询：带有bob学生描述的数据是属于哪个班级的：对象名小写__属性 grade=Grades.objects.filter(Students__scontend__contains="bob") print(grade) return render(request,'myapp/students.html', {"students":stulist}) # F对象：比较同一个对象下不同的属性：例如找出girlnum>boynum的班级,支持算数运算 from django.db.models import F,Q def grades_comparison(request): g=Grades.objects.filter(ggirlnum__gt=F('gboynum')+20) print(g) return HttpResponse("yes") def addstudent(request): grade=Grades.objects.get(pk=2) stu=Students.createStudent("li",25,True,"I am li",grade,"2018-5-1", "2017-5-2") stu.save() return HttpResponse("Hello") def addstudent2(request): grade=Grades.objects.get(pk=1) stu=Students.stu_objects.createStudent2("bob",25,True,"I am bob",grade,"2018-5-1", "2017-5-2") stu.save() # stu=Students.stu_objects.createStudent2() return HttpResponse("hello")
from django.db import models # Create your models here. # -*- coding: utf-8 -*- class Grades(models.Model): gname=models.CharField(max_length=20) gdate=models.DateTimeField() ggirlnum=models.IntegerField() gboynum=models.IntegerField() isDelete=models.BooleanField(default=False) def __str__(self): return self.gname class Meta: db_table="grades" ordering=['id'] class StudentsManager(models.Manager): def get_queryset(self): return super(StudentsManager,self).get_queryset().filter(isDelete=False) def createStudent2(self, name, age, gender, contend, grade, lastT, createT, isD=False): # def createStudent2(self): stu=self.model() print(type(stu)) stu.sname=name stu.sage=age stu.sgender = gender stu.scontend=contend stu.sgrade=grade stu.lasttime=lastT stu.createtime=createT return stu class Students(models.Model): #自定义管理器 stu_objects=StudentsManager() stu_object=models.Manager() sname=models.CharField(max_length=20) sgender=models.BooleanField(default=True) sage=models.IntegerField(db_column="age") scontend=models.CharField(max_length=20) isDelete=models.BooleanField(default=False) # 关联外键 # -对多（外键在多的地方关联） sgrade=models.ForeignKey("Grades") # 说明：1.不需要定义主键,自动生成,且自动增加gra def __str__(self): return self.sname lasttime=models.DateTimeField(auto_now=True) createtime=models.DateTimeField(auto_now_add=True) class Meta: db_table="students" ordering=['id'] @classmethod def createStudent(cls,name,age,gender,contend,grade,lastT,createT,isD=False): stu=cls(sname=name,sage=age,sgender=gender,scontend=contend,\ lasttime=lastT,sgrade=grade,createtime=createT,isDelete=isD) return stu
from django.conf.urls import url,include from.import views urlpatterns=[ url(r'^$',views.index), url(r'^students/$',views.stu), url(r'^addstudent/$',views.addstudent), url(r'^addstudent2/$',views.addstudent2), url(r'^stu2/$',views.stu2), url('^stu/(\d+)$',views.stupage), url('^stusearch$',views.stusearch), url('^gra$',views.grades_comparison) ]
html> <html lang="en"> <head> <meta charset="UTF-8"> <title>学生信息title> head> <body> <h1>学生信息列表h1> <ul> {% for student in students %} <li> {{ student.sname }}--{{ student.scontend }} li> {% endfor %} ul> body> html>