模型二 – 常用查詢和表關係的實現
一:字段類型+參數
字段類型：https://docs.djangoproject.com/en/2.1/ref/models/fields/#field-types
字段參數：https://docs.djangoproject.com/en/2.1/ref/models/fields/#field-options常用查詢
二：常用查詢
# get all filter
# all
In [8]: Student.objects.all()
Out[8]: <QuerySet [<Student: Lucy>, <Student: lucy>, <Student: 趙小瑋>, <Student: 李國林>, <Student: lily>]>
# filter
In [10]: res = Student.objects.filter(name="lily")
In [11]: print(res.query)
SELECT `teacher_student`.`num`, `teacher_student`.`name`, `teacher_student`.`age`, `teacher_student`.`height`, `teacher_student`.`sex`, `teacher_student`.`qq`, `teacher_student`.`phone`, `teacher_student`.`c_time`, `teacher_student`.`x_time` FROM `teacher_student` WHERE `teacher_student`.`name` = lily
# get
In [12]: Student.objects.get(name="lily")
Out[12]: <Student: lily>
共同點:
都是通過objects去實現的----》objects：每個django模型類，都有一個默認的管理器，objects
查詢方法：
In [13]: Student.objects.first() # 查詢第一條數據
Out[13]: <Student: Lucy> # 返回一個對象
In [14]: Student.objects.last() # 查詢最後一條數據
Out[14]: <Student: lily> # 返回一個對象
In [15]: Student.objects.filter(name="lily")
Out[15]: <QuerySet [<Student: lily>]>
In [16]: Student.objects.exclude(name="lily") # 與filter用法相同，作用相反，排除的意思
Out[16]: <QuerySet [<Student: Lucy>, <Student: lucy>, <Student: 趙小瑋>, <Student: 李國林>]>
In [19]: Student.objects.values('name') # 指定字段查詢：只能拿到指定查詢的字段值，其他的無法獲取
Out[19]: <QuerySet [{'name': 'Lucy'}, {'name': 'lucy'}, {'name': '趙小瑋'}, {'name': '李國林'}, {'name': 'lily'}]>
In [20]: res = Student.objects.values('name')
In [21]: res[2]['name']
Out[21]: '趙小瑋'
# only ：指定字段查詢，但是可以獲取其他所有字段值
In [26]: res = Student.objects.only('name')
In [27]: res
Out[27]: <QuerySet [<Student: Lucy>, <Student: lucy>, <Student: 趙小瑋>, <Student: 李國林>, <Student: lily>]>
In [28]: res[2].name
Out[28]: '趙小瑋'
In [29]: res[2].sex
Out[29]: 1
# defer：和only相反
# order_by:根據指定字段排序
In [34]: res = Student.objects.order_by('age')
In [35]: print(res.query)
SELECT `teacher_student`.`num`, `teacher_student`.`name`, `teacher_student`.`age`, `teacher_student`.`height`, `teacher_student`.`sex`, `teacher_student`.`qq`, `teacher_student`.`phone`, `teacher_student`.`c_time`, `teacher_student`.`x_time` FROM `teacher_student` ORDER BY `teacher_student`.`age` ASC
In [36]: res
Out[36]: <QuerySet [<Student: Lucy>, <Student: lucy>, <Student: lily>, <Student: 李國林>, <Student: 趙小瑋>]>
In [37]: res = Student.objects.order_by('-age')
In [38]: print(res.query)
SELECT `teacher_student`.`num`, `teacher_student`.`name`, `teacher_student`.`age`, `teacher_student`.`height`, `teacher_student`.`sex`, `teacher_student`.`qq`, `teacher_student`.`phone`, `teacher_student`.`c_time`, `teacher_student`.`x_time` FROM `teacher_student` ORDER BY `teacher_student`.`age` DESC
In [39]: res
Out[39]: <QuerySet [<Student: 趙小瑋>, <Student: 李國林>, <Student: lily>, <Student: lucy>, <Student: Lucy>]>
# 多條件查詢
In [42]: Student.objects.filter(age=18,sex=0)
Out[42]: <QuerySet [<Student: lily>]>
In [43]: from django.db.models import Q
In [44]: Student.objects.filter(Q(sex=0),Q(age=18)|Q(age=12))
Out[44]: <QuerySet [<Student: Lucy>, <Student: lily>]>
查詢條件
# exact：準確匹配
.....WHERE `teacher_student`.`name` = lucy
# iexact:不區分大小寫匹配
.....WHERE `teacher_student`.`name` LIKE lucy
# contains:包含匹配
..... WHERE `teacher_student`.`name` LIKE BINARY %l%
# icontains:不區分大小寫包含匹配
......WHERE `teacher_student`.`name` LIKE %L%
# in:指定值
Student.objects.filter(sex__in='01')
Student.objects.filter(pk__in=[1,3,5])
# 子查詢
res = Student.objects.filter(name__icontains='l').only("name")
res1 = Student.objects.filter(pk__in=res).only("name")
SELECT `teacher_student`.`num`, `teacher_student`.`name` FROM `teacher_student` WHERE `teacher_student`.`num` IN (SELECT U0.`num` FROM `teacher_student` U0 WHERE U0.`name` LIKE %l%)
# gt 大於 gte大於等於 lt小於 lte小於等於
Student.objects.filter(pk__gt=2)
# 範圍查詢
res = Student.objects.filter(age__range=(18, 30))
# annotate： 分組
In [66]: res = Student.objects.values('sex').annotate(ren=Count('sex')) # 聚合分組
In [67]: print(res.query)
SELECT `teacher_student`.`sex`, COUNT(`teacher_student`.`sex`) AS `ren` FROM `teacher_student` GROUP BY `teacher_student`.`sex` ORDER BY NULL
表關係的實現
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1.表關係
from django.db import models
# Create your models here.
class Student(models.Model):
name = models.CharField('姓名', max_length=20)
age = models.SmallIntegerField('年齡', null=True)
sex = models.SmallIntegerField('性別', default=1)
qq = models.CharField('QQ', max_length=20, unique=True)
phone = models.CharField('電話', max_length=20, unique=True)
c_time = models.DateTimeField('創建時間', auto_now_add=True)
# detail = models.OneToOneField('StudentDetail', on_delete=models.SET_NULL, null=True)
grade = models.ForeignKey('Grade', on_delete=models.SET_NULL, null=True)
def __str__(self):
return "{}-{}".format(self.name, self.age)
class StudentDetail(models.Model):
college = models.CharField('學院', max_length=20)
student = models.OneToOneField('Student', on_delete=models.CASCADE)
class Grade(models.Model):
name = models.CharField("班級名稱", max_length=20)
num = models.CharField("班期", max_length=20)
class Course(models.Model):
name = models.CharField("課程名稱", max_length=20)
students = models.ManyToManyField('Student', through='Enroll')
# 中間表
class Enroll(models.Model):
student = models.ForeignKey('Student', on_delete=models.CASCADE)
course = models.ForeignKey('Course', on_delete=models.CASCADE)
pay = models.FloatField('繳費金額', default=0)
c_time = models.DateTimeField('報名時間', auto_now_add=True)
2.回滾
python manage.py migrate student 0001
注意：回滾後刪除最後一次遷移文件