如何使用south将数据从字段迁移到表中的另一个字段

Question

我正在使用南方进行模式迁移的Django项目。 我有以下情况：

模式

class Book(model.Models):
    name = models.CharField(max_length=255, blank=True)
    bid = models.IntegerField(blank=True, null=True)

class Author(model.Models):
   name = models.CharField(max_length=255, blank=True)
   book_id = models.ForeignKey(Book, null=True, to_field="bid", db_column="bookID")

我想将作者模型更改为以下内容：

class Author(model.Models):
   name = models.CharField(max_length=255, blank=True)
   book = models.ForeignKey(Book, null=True, db_column="book_id")

但没有松散的数据。我想按出价搜索每本书，并在作者模型中将找到的那个分配给新字段。

由于

Answer 1

您必须进行3次迁移。一个schemamgiration，它添加新书FK，然后是数据迁移，然后是一个schemamigration来删除和重命名字段。

因此，您想要将models.py文件更改为：

class Book(model.Models):
    name = models.CharField(max_length=255, blank=True)
    bid = models.IntegerField(blank=True, null=True)

class Author(model.Models):
   name = models.CharField(max_length=255, blank=True)
   book_id = models.ForeignKey(Book, null=True, to_field="bid", db_column="bookID")
   # You don't need the db_column="book_id" since that's what it does at the DB level by default.
   # I'm not sure if things will break if you name it book with another field as book_id.
   book_new = models.ForeignKey(Book, null=True) 

然后运行python manage.py schemamigration APP_NAME auto 然后运行```python manage.py datamigration APP_NAME populate_book_id

然后编辑新创建的数据迁移并循环通过Author实例设置带有book_id字段的新书字段。不要忘记在向后方法中删除书籍字段值。

然后将models.py文件更改为以下内容：

class Book(model.Models):
    name = models.CharField(max_length=255, blank=True)
    bid = models.IntegerField(blank=True, null=True)

class Author(model.Models):
   name = models.CharField(max_length=255, blank=True)
   # You don't need the db_column="book_id" since that's what it does at the DB level by default.
   book = models.ForeignKey(Book, null=True) 

然后运行python manage.py schemamigration APP_NAME auto 您需要检查最后一次架构迁移，以确保它将book_new重命名为book，而不是删除和创建列。 Here's an answer that explains how to change it.