學(xué)習(xí)筆記，僅供參考

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數(shù)據(jù)庫的遷移

我在學(xué)習(xí)一對多映射時，由于操作不慎，導(dǎo)致報錯頻頻，現(xiàn)在，我就來解決這個問題，順便學(xué)習(xí)一下遷移操作。

現(xiàn)在，我在第7次遷移時出錯了，它的錯誤是這樣的：

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

報錯信息顯示，pub字段不在china_publisher表中。

我修改之后，還有一個報錯，它是這樣的：

django.db.utils.InternalError: (1366, "Incorrect integer value: '清華大學(xué)出版社' for column 'pub_id' at row 1")

錯誤太多，我也不知道該怎么辦，所以我選擇回到前幾次遷移文件，重新開始。

看一下項目目錄，方便后續(xù)理解：

目前，我在第7次遷移的位置，我想回到第1次遷移，那該咋整呢？

我們可以在cmd中敲入如下代碼：

python manage.py migrate bookstore 0001

輸出：

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

這里，我從0007退到0005，發(fā)現(xiàn)Django還是可能會報錯，就再退到0002，發(fā)現(xiàn)Django依然可能會報錯，最后退到0001，也就是說我敲入了3次退回代碼。上面顯示的輸出，是我從0002退回到0001的輸出。

我們查看一下數(shù)據(jù)庫：

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)

此時的數(shù)據(jù)庫應(yīng)該沒有china_publisher數(shù)據(jù)表，不知道哪里出錯了，這種情況和Django在0001遷移文件里記錄的情況完全不同，所以我果斷將其刪除！

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

一般情況下，還是不要隨便刪表，要不然很容易出現(xiàn)混亂。

現(xiàn)在，我們把0001以上的記錄文件全部刪除：

并再次進行遷移操作

F:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py ma kemigrations Migrations 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 mi grate Operations to perform:Apply all migrations: admin, auth, bookstore, contenttypes, sessions Running migrations:Applying bookstore.0002_auto_20200622_0213... OK

遷移成功！

查看一下數(shù)據(jù)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開發(fā)實戰(zhàn) | 0.00 | 0.00 | | 2 | python | 0.00 | 0.00 | | 3 | R | 0.00 | 0.00 | | 5 | 算法 | 0.00 | 0.00 | | 6 | 集體智慧編程 | 0.00 | 0.00 | +----+-------------------+------------+-------+ 5 rows in set (0.00 sec)

這時，我們在Book模型類中再加入一個字段pub，并與Publisher模型類進行一對多關(guān)聯(lián)：

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("初版書籍總量", default = 0)tele = models.CharField("聯(lián)系電話", 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("書名", max_length = 30)exfacPrice = models.DecimalField("出廠價", max_digits = 6, decimal_places = 2,default = 0)price = models.DecimalField("售價", max_digits = 6, decimal_places = 2,default = 0)pub = models.ForeignKey(Publisher, on_delete = models.CASCADE , null=True)def __str__(self):string = "書名:%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("年齡", null = False,default = 1)email = models.EmailField("郵箱", null = True)def __str__(self):string = "姓名:{}, 年齡:{}".format(self.name, self.age) return stringclass Partner(models.Model):'''作家伴侶模型類'''name = models.CharField("姓名", max_length=50)age = models.IntegerField("年齡", null = False,default = 1)author = models.OneToOneField(Author, on_delete = models.CASCADE)

再次執(zhí)行遷移操作：

F:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py makemigrations Migrations for 'bookstore':bookstore\migrations\0003_book_pub.py- Add field pub to bookF:\MyStudio\PythonStudio\goatbishop.project01\Django\mywebsite_db>python manage.py migrate Operations to perform:Apply all migrations: admin, auth, bookstore, contenttypes, sessions Running migrations:Applying bookstore.0003_book_pub... OK

遷移成功！

再次查看bookstore_book數(shù)據(jù)表：

mysql> select * from bookstore_book; +----+-------------------+------------+-------+--------+ | id | title | exfacPrice | price | pub_id | +----+-------------------+------------+-------+--------+ | 1 | Djangoweb開發(fā)實戰(zhàn) | 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 | 集體智慧編程 | 0.00 | 0.00 | NULL | +----+-------------------+------------+-------+--------+ 5 rows in set (0.00 sec)

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