Django(part33)--数据库的迁移（django重新生成迁移）

Django(part33)--数据库的迁移（django重新生成迁移）

学习笔记，仅供参考

数据库的迁移

我在学习一对多映射时，由于操作不慎，导致报错频频，现在，我就来解决这个问题，顺便学习一下迁移操作。

现在，我在第7次迁移时出错了，它的错误是这样的：

pymysql.err.InternalError: (1054, "Unknown column 'pub' in 'china_publisher'")

报错信息显示，pub字段不在china_publisher表中。

我修改之后，还有一个报错，它是这样的：

django.db.utils.InternalError: (1366, "Incorrect integer value: '清华大学出版社' for column 'pub_id' at row 1")

错误太多，我也不知道该怎么办，所以我选择回到前几次迁移文件，重新开始。

看一下项目目录，方便后续理解：

目前，我在第7次迁移的位置，我想回到第1次迁移，那该咋整呢？

我们可以在cmd中敲入如下代码：

python manage.py migrate bookstore 0001

输出：

Operations to perform: Target specific migration: 0001_initial, from bookstoreRunning migrations: Rendering model states... DONE Unapplying bookstore.0002_author... OK

这里，我从0007退到0005，发现Django还是可能会报错，就再退到0002，发现Django依然可能会报错，最后退到0001，也就是说我敲入了3次退回代码。上面显示的输出，是我从0002退回到0001的输出。

我们查看一下数据库：

mysql> show tables;+----------------------------+| Tables_in_mywebdb |+----------------------------+| auth_group || auth_group_permissions || auth_permission || auth_user || auth_user_groups || auth_user_user_permissions || bookstore_book || china_publisher || django_admin_log || django_content_type || django_migrations || django_session |+----------------------------+12 rows in set (0.00 sec)

此时的数据库应该没有china_publisher数据表，不知道哪里出错了，这种情况和Django在0001迁移文件里记录的情况完全不同，所以我果断将其删除！

mysql> drop table china_publisher;Query OK, 0 rows affected (0.03 sec)

一般情况下，还是不要随便删表，要不然很容易出现混乱。

现在，我们把0001以上的记录文件全部删除：

并再次进行迁移操作

F:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py makemigrationsMigrations for 'bookstore': bookstore\migrations\0002_auto_20200622_0213.py - Create model Author - Create model Publisher - Remove field pub from book - Add field exfacPrice to book - Add field price to book - Create model PartnerF:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py migrateOperations to perform: Apply all migrations: admin, auth, bookstore, contenttypes, sessionsRunning migrations: Applying bookstore.0002_auto_20200622_0213... OK

迁移成功！

查看一下数据表：

mysql> show tables;+----------------------------+| Tables_in_mywebdb |+----------------------------+| auth_group || auth_group_permissions || auth_permission || auth_user || auth_user_groups || auth_user_user_permissions || bookstore_author || bookstore_book || bookstore_partner || china_publisher || django_admin_log || django_content_type || django_migrations || django_session |+----------------------------+14 rows in set (0.00 sec)mysql> select * from china_publisher;Empty set (0.00 sec)mysql> select * from bookstore_book;+----+-------------------+------------+-------+| id | title | exfacPrice | price |+----+-------------------+------------+-------+| 1 | Djangoweb开发实战 | 0.00 | 0.00 || 2 | python | 0.00 | 0.00 || 3 | R | 0.00 | 0.00 || 5 | 算法 | 0.00 | 0.00 || 6 | 集体智慧编程 | 0.00 | 0.00 |+----+-------------------+------------+-------+5 rows in set (0.00 sec)

这时，我们在Book模型类中再加入一个字段pub，并与Publisher模型类进行一对多关联：

from django.db import models# Create your models here.class Publisher(models.Model): name = models.CharField("出版社名", max_length = 50,null = True) booknumber = models.PositiveIntegerField("初版书籍总量", default = 0) tele = models.CharField("联系电话", max_length = 11, null = False) class Meta: db_table = "china_publisher" verbose_name = "ChinaPublisher" verbose_name_plural = "ChinaPublishers" def __str__(self): string = "出版社:%s" % (self.name) return stringclass Book(models.Model): title = models.CharField("书名", max_length = 30) exfacPrice = models.DecimalField("出厂价", max_digits = 6, decimal_places = 2, default = 0) price = models.DecimalField("售价", max_digits = 6, decimal_places = 2, default = 0) pub = models.ForeignKey(Publisher, on_delete = models.CASCADE , null=True) def __str__(self): string = "书名:%s" % (self.title) return stringclass Author(models.Model): name = models.CharField("姓名", max_length = 30, null = False, unique = True, db_index = True) age = models.IntegerField("年龄", null = False, default = 1) email = models.EmailField("邮箱", null = True) def __str__(self): string = "姓名:{}, 年龄:{}".format(self.name, self.age) return string class Partner(models.Model): '''作家伴侣模型类''' name = models.CharField("姓名", max_length=50) age = models.IntegerField("年龄", null = False, default = 1) author = models.OneToOneField(Author, on_delete = models.CASCADE)

再次执行迁移操作：

F:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py makemigrationsMigrations for 'bookstore': bookstore\migrations\0003_book_pub.py - Add field pub to bookF:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py migrateOperations to perform: Apply all migrations: admin, auth, bookstore, contenttypes, sessionsRunning migrations: Applying bookstore.0003_book_pub... OK

迁移成功！

再次查看bookstore_book数据表：

mysql> select * from bookstore_book;+----+-------------------+------------+-------+--------+| id | title | exfacPrice | price | pub_id |+----+-------------------+------------+-------+--------+| 1 | Djangoweb开发实战 | 0.00 | 0.00 | NULL || 2 | python | 0.00 | 0.00 | NULL || 3 | R | 0.00 | 0.00 | NULL || 5 | 算法 | 0.00 | 0.00 | NULL || 6 | 集体智慧编程 | 0.00 | 0.00 | NULL |+----+-------------------+------------+-------+--------+5 rows in set (0.00 sec)

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