Django更新models数据库结构步骤

砸漏

发布于 2020-11-04 15:11:29

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发布于 2020-11-04 15:11:29

文章被收录于专栏：恩蓝脚本

有时候在我们使用Django设计了models中的数据库结构，并且已经同步了数据库之后，我们突然想在数据表中更新或者增加新的字段，也就是需要修改数据库的结构，会出现以下的问题：

C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations You are trying to add a non-nullable field ‘grade’ to student without a default; we can’t do that (the dat abase needs something to populate existing rows). Please select a fix: 1) Provide a one-off default now (will be set on all existing rows with a null value for this column) 2) Quit, and let me add a default in models.py Select an option:

就是在我们在models中修改了表的字段后，进行python manage.py makemigrations同步数据库时会出现上面报错，会导致数据库结构更新失败

解决方法如下：

第一种方式：先删除再重构

1、删除数据库对应的数据表

注意：在这里可以不用暴力删除数据表，可以利用django的migrations进行，操作如下：

1.1、首先将自己需要重构的数据表类的models注释掉，然后输入命令python manage.py makemigrations，这个时候migration会自动记录删除数据表的操作

1.2、然后在输入命令python manage.py migrate，Django会自动将本地对应的数据库进行删除

2、删除应用当中的migrations文件

3、删除应用当中的pychace文件

4、删除db_sqllite文件（若配置数据库为mysql时，可以删除db_sqllite）

5、建立一个空数据库，命令为python manage.py makemigrations –empty 应用名称

C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations –empty bbs Migrations for ‘bbs’: bbs\migrations\0001_initial.py

6、同步数据库：

python manage.py makemigrations
python manage.py migrate

 
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations --empty bbs
Migrations for 'bbs':
 bbs\migrationspython manage.py makemigrations
python manage.py migrate
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations --empty bbs
Migrations for 'bbs':
bbs\migrations\0001_initial.py
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations
Migrations for 'bbs':
bbs\migrations\0002_student_testmyfield.py
- Create model Student
- Create model Testmyfield
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py migrate
Operations to perform:
Apply all migrations: admin, auth, bbs, contenttypes, sessions
Running migrations:
Applying contenttypes.0001_initial... OK
Applying auth.0001_initial... OK
Applying admin.0001_initial... OK
Applying admin.0002_logentry_remove_auto_add... OK
Applying contenttypes.0002_remove_content_type_name... OK
Applying auth.0002_alter_permission_name_max_length... OK
Applying auth.0003_alter_user_email_max_length... OK
Applying auth.0004_alter_user_username_opts... OK
Applying auth.0005_alter_user_last_login_null... OK
Applying auth.0006_require_contenttypes_0002... OK
Applying auth.0007_alter_validators_add_error_messages... OK
Applying auth.0008_alter_user_username_max_length... OK
Applying bbs.0001_initial... OK
Applying bbs.0002_student_testmyfield... OK
Applying sessions.0001_initial... OK
01_initial.py
 
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations
Migrations for 'bbs':
 bbs\migrationspython manage.py makemigrations
python manage.py migrate
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations --empty bbs
Migrations for 'bbs':
bbs\migrations\0001_initial.py
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py makemigrations
Migrations for 'bbs':
bbs\migrations\0002_student_testmyfield.py
- Create model Student
- Create model Testmyfield
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py migrate
Operations to perform:
Apply all migrations: admin, auth, bbs, contenttypes, sessions
Running migrations:
Applying contenttypes.0001_initial... OK
Applying auth.0001_initial... OK
Applying admin.0001_initial... OK
Applying admin.0002_logentry_remove_auto_add... OK
Applying contenttypes.0002_remove_content_type_name... OK
Applying auth.0002_alter_permission_name_max_length... OK
Applying auth.0003_alter_user_email_max_length... OK
Applying auth.0004_alter_user_username_opts... OK
Applying auth.0005_alter_user_last_login_null... OK
Applying auth.0006_require_contenttypes_0002... OK
Applying auth.0007_alter_validators_add_error_messages... OK
Applying auth.0008_alter_user_username_max_length... OK
Applying bbs.0001_initial... OK
Applying bbs.0002_student_testmyfield... OK
Applying sessions.0001_initial... OK
02_student_testmyfield.py
 - Create model Student
 - Create model Testmyfield
 
C:\Users\Administrator\Desktop\Web开发\Django_Demo\jkxy python manage.py migrate
Operations to perform:
 Apply all migrations: admin, auth, bbs, contenttypes, sessions
Running migrations:
 Applying contenttypes.0001_initial... OK
 Applying auth.0001_initial... OK
 Applying admin.0001_initial... OK
 Applying admin.0002_logentry_remove_auto_add... OK
 Applying contenttypes.0002_remove_content_type_name... OK
 Applying auth.0002_alter_permission_name_max_length... OK
 Applying auth.0003_alter_user_email_max_length... OK
 Applying auth.0004_alter_user_username_opts... OK
 Applying auth.0005_alter_user_last_login_null... OK
 Applying auth.0006_require_contenttypes_0002... OK
 Applying auth.0007_alter_validators_add_error_messages... OK
 Applying auth.0008_alter_user_username_max_length... OK
 Applying bbs.0001_initial... OK
 Applying bbs.0002_student_testmyfield... OK
 Applying sessions.0001_initial... OK

第二种方式：直接在原结构上更新结构

#出版社
class Publisher(models.Model):
 '''出版社数据表'''
 id=models.AutoField(primary_key=True) #自增ID主键
 name=models.CharField(max_length=50,verbose_name='出版社名称',null=False,unique=True)
 
 def __str__(self):
  return '{},{}'.format(self.id,self.name)

接下来我们需要新增一个字段addr地址

#出版社
class Publisher(models.Model):
 '''出版社数据表'''
 id=models.AutoField(primary_key=True) #自增ID主键
 name=models.CharField(max_length=50,verbose_name='出版社名称',null=False,unique=True)
 addr=models.CharField(max_length=128,verbose_name='出版社地址')
 
 def __str__(self):
  return '{},{}'.format(self.id,self.name,self.addr)

由于我们的数据库的Publisher表本身已经有数据了，所以我们在进行python manage.py makemigrations会出现以下错误：

上图的意思是说addr没有默认值，无法更新到数据库中，然后给出了两个选项：

第一是让你马上给定一个默认值，然后一次性的把所有addr都写成这个值

第二是先退出，你自己在models里面去配置默认值

我选择先退出，在models中加上默认值，在进行makemigrations，这次就会更新成功了！

#出版社
class Publisher(models.Model):
 '''出版社数据表'''
 id=models.AutoField(primary_key=True) #自增ID主键
 name=models.CharField(max_length=50,verbose_name='出版社名称',null=False,unique=True)
 addr=models.CharField(max_length=128,verbose_name='出版社地址',default='成都市动物园')
 
 def __str__(self):
  return '{},{}'.format(self.id,self.name,self.addr)