Python Django 数据库的相关操作详解

from djanGo.db import models
class Student(models.Model):
    """
    学生表
    """
    name = models.CharField('学生姓名', max_length=200, unique=True, help_text='学生姓名')
    gender = models.SmallIntegerField('性别', default='1', help_text='性别')
    hobby = models.CharField('爱好', max_length=200, null=True, blank=True, help_text='兴趣爱好')
    create_time = models.DateTimeField('创建时间', auto_now_add=True, help_text='创建时间')
    class Meta:
        """
        元数据，
        """
        db_table = 'student'  # 指定当前模型创建的表明,不写默认当前的模型名Student
        verbose_name = '学生信息表'  # 注释
        verbose_name_plural = verbose_name  # 指定为复数
        ordering = ['-create_time']  # 使用创建时间倒序排序，不加-为正序
    def __str__(self):
        return self.name  # 方便于调式，下面操作数据库时会体现出来

# 日志配置
LOGGING = {
    'version': 1,
    'handlers': {
        'console': {
            'class': 'logging.StreamHandler'
        }
    },
    'loggers': {
        'django': {
            'handlers': ['console'],
            'level': 'DEBUG',
            'propagate': False
        }
    }
}

# 导入模型类
In [1]: from project2s.models import Student
# 实例化对象，传入必传字段
In [2]: s = Student(name='test',hobby='打篮球')
# 调用save方法保存到数据库，
In [3]: s.save()
# 输出内容如下：其底层还是使用的INSERT语句
(0.031) INSERT INTO `student` (`name`, `gender`, `hobby`, `create_time`) VALUES ('test', 1, '打篮球', '2021-11-10 12:49:13.814987') RETURNING `student`.`id`; args=('test', 1, '打篮球',
 '2021-11-10 12:49:13.814987')

In [2]: s1 = Student()
In [3]: s1.name = 'test1'
In [4]: s1.hobby = '唱歌'
In [5]: s1.save()
(0.031) INSERT INTO `student` (`name`, `gender`, `hobby`, `create_time`) VALUES ('test1', 1, '唱歌', '2021-11-10 13:13:41.183826') RETURNING `student`.`id`; args=('test1', 1, '唱歌', '
2021-11-10 13:13:41.183826')

In [6]: s1.name = '测试'
In [7]: s1.save()
(0.031) UPDATE `student` SET `name` = '测试', `gender` = 1, `hobby` = '唱歌', `create_time` = '2021-11-10 13:13:41.183826' WHERE `student`.`id` = 2; args=('测试', 1, '唱歌', '2021-11-1
0 13:13:41.183826', 2)

# 前面已经实例化过s2=Student(name='张三',hobby='唱歌')
In [11]: s2.name = '李四'
In [12]: s2.save(update_fields=['name'])
(0.047) UPDATE `student` SET `name` = '李四' WHERE `student`.`id` = 4; args=('李四', 4)

In [2]: Student.objects.all().update(hobby='玩游戏')
(0.031) UPDATE `student` SET `hobby` = '玩游戏'; args=('玩游戏',)
Out[2]: 3

In [4]: Student.objects.all()
Out[4]: (0.094) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` DESC LIMIT 21; a
rgs=()
<QuerySet [<Student: 李四>, <Student: 测试>, <Student: test>]>
# 转换成列表
In [5]: list(Student.objects.all())
(0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` DESC; args=()
Out[5]: [<Student: 李四>, <Student: 测试>, <Student: test>]

# 通过索引
In [6]: Student.objects.all()[0]
(0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` DESC LIMIT 1; args=()
Out[6]: <Student: 李四>

# 通过切片
In [5]: Student.objects.all()[:2] # 等价于 LIMIT 2
Out[5]: (0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` DESC LIMIT 2; ar
gs=()
<QuerySet [<Student: 李四>, <Student: 测试>]>

In [4]: Student.objects.all()[1:2] # 等价于 LIMIT 1 OFF SET 1
Out[4]: (0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` DESC LIMIT 1 OFF
SET 1; args=()
<QuerySet [<Student: 测试>]>

In [4]: Student.objects.all().filter(name='李四')
Out[4]: (0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` WHERE `student`.`name` = '李四' ORDER BY `student
`.`create_time` DESC LIMIT 21; args=('李四',)
<QuerySet [<Student: 李四>]>

In [4]: Student.objects.all().exclude(name='李四')
Out[4]: (0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` WHERE NOT (`student`.`name` = '李四') ORDER BY `s
tudent`.`create_time` DESC LIMIT 21; args=('李四',)
<QuerySet [<Student: 测试>, <Student: test>]>

In [4]: Student.objects.all().get(pk=1)
(0.047) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` WHERE `student`.`id` = 1 LIMIT 21; args=(1,)
Out[4]: <Student: test>

In [5]: Student.objects.all().first()
(0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` DESC LIMIT 1; args=()
Out[5]: <Student: 李四>

In [6]: Student.objects.all().last()
(0.031) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`create_time` ASC LIMIT 1; args=()
Out[6]: <Student: test>

In [3]: Student.objects.all().order_by('name')
Out[3]: (0.047) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`name` ASC LIMIT 21; args=()
<QuerySet [<Student: test>, <Student: 李四>, <Student: 测试>]>

In [4]: Student.objects.all().order_by('-name')
Out[4]: (0.047) SELECT `student`.`id`, `student`.`name`, `student`.`gender`, `student`.`hobby`, `student`.`create_time` FROM `student` ORDER BY `student`.`name` DESC LIMIT 21; args=()
<QuerySet [<Student: 测试>, <Student: 李四>, <Student: test>]>