我在想,如果以下迁移是可能的Django的南部和仍然保留的数据。
之前: 我目前有两个应用程序,一个叫做电视,一个叫做电影,每个都有一个VideoFile模型(在这里简化):
tv/models.py:
class VideoFile(models.Model): show = models.ForeignKey(Show, blank=True, null=True) name = models.CharField(max_length=1024, blank=True) size = models.IntegerField(blank=True, null=True) ctime = models.DateTimeField(blank=True, null=True)
movies/models.py:
class VideoFile(models.Model): movie = models.ForeignKey(Movie, blank=True, null=True) name = models.CharField(max_length=1024, blank=True) size = models.IntegerField(blank=True, null=True) ctime = models.DateTimeField(blank=True, null=True)
后: 因为这两个videofile对象是如此相似,所以我想摆脱重复并在一个名为media的单独应用中创建一个新模型,其中包含通用的VideoFile类并使用继承对其进行扩展:
media / models.py:
class VideoFile(models.Model): name = models.CharField(max_length=1024, blank=True) size = models.IntegerField(blank=True, null=True) ctime = models.DateTimeField(blank=True, null=True)
class VideoFile(media.models.VideoFile): show = models.ForeignKey(Show, blank=True, null=True)
class VideoFile(media.models.VideoFile): movie = models.ForeignKey(Movie, blank=True, null=True)
所以我的问题是,如何使用django-south做到这一点并仍然维护现有数据?
所有这三个应用程序都已经由南迁移管理,根据南文档,将模式迁移和数据迁移结合起来是不明智的做法,他们建议应分几步完成。
我认为可以使用这样的单独迁移来完成(假设已经创建了media.VideoFile)
我确实尝试遍历了T Stone概述的解决方案,尽管我认为这是一个了不起的入门,并解释了应该如何做,但我遇到了一些问题。
我认为大多数情况下,你不再需要为父类创建表条目,即你不需要
new_movie.videofile_ptr = orm['media.VideoFile'].objects.create()
不再。Django现在会自动为你执行此操作(如果你有非null字段,则以上内容对我不起作用,并给我一个数据库错误)。
我认为这可能是由于django和south的变化所致,这是一个适用于Django 1.2.3和south 0.7.1的ubuntu 10.10的版本。这些模型有些不同,但是你将获得要点:
初始设置 post1 / models.py:
class Author(models.Model): first = models.CharField(max_length=30) last = models.CharField(max_length=30) class Tag(models.Model): name = models.CharField(max_length=30, primary_key=True) class Post(models.Model): created_on = models.DateTimeField() author = models.ForeignKey(Author) tags = models.ManyToManyField(Tag) title = models.CharField(max_length=128, blank=True) content = models.TextField(blank=True)
post2 / models.py:
class Author(models.Model): first = models.CharField(max_length=30) middle = models.CharField(max_length=30) last = models.CharField(max_length=30) class Tag(models.Model): name = models.CharField(max_length=30) class Category(models.Model): name = models.CharField(max_length=30) class Post(models.Model): created_on = models.DateTimeField() author = models.ForeignKey(Author) tags = models.ManyToManyField(Tag) title = models.CharField(max_length=128, blank=True) content = models.TextField(blank=True) extra_content = models.TextField(blank=True) category = models.ForeignKey(Category)
显然有很多重叠之处,因此我想将通用性分解为通用的后期模型,而只保留其他模型类中的差异。
新设置:
genpost / models.py:
class Author(models.Model): first = models.CharField(max_length=30) middle = models.CharField(max_length=30, blank=True) last = models.CharField(max_length=30) class Tag(models.Model): name = models.CharField(max_length=30, primary_key=True) class Post(models.Model): created_on = models.DateTimeField() author = models.ForeignKey(Author) tags = models.ManyToManyField(Tag) title = models.CharField(max_length=128, blank=True) content = models.TextField(blank=True)
post1 / models.py:
import genpost.models as gp class SimplePost(gp.Post): class Meta: proxy = True post2 / models.py: import genpost.models as gp class Category(models.Model): name = models.CharField(max_length=30) class ExtPost(gp.Post): extra_content = models.TextField(blank=True) category = models.ForeignKey(Category)
如果你想继续前进,首先需要将这些模型推向南方:
$./manage.py schemamigration post1 --initial $./manage.py schemamigration post2 --initial $./manage.py migrate
迁移数据 怎么做呢?首先编写新的应用程序genpost,然后向南进行初始迁移:
$./manage.py schemamigration genpost --initial
(我$用来表示shell提示符,所以请不要键入。)
接下来,分别在post1 / models.py和post2 / models.py中创建新类SimplePost和ExtPost(请不要删除其余的类)。然后也为这两个创建schemamigrations:
$./manage.py schemamigration post1 --auto $./manage.py schemamigration post2 --auto
现在我们可以应用所有这些迁移:
$./manage.py migrate
让我们开始讨论,将数据从post1和post2迁移到genpost:
$./manage.py datamigration genpost post1_and_post2_to_genpost --freeze post1 --freeze post2
然后编辑genpost / migrations / 0002_post1_and_post2_to_genpost.py:
class Migration(DataMigration): def forwards(self, orm): # # Migrate common data into the new genpost models # for auth1 in orm['post1.author'].objects.all(): new_auth = orm.Author() new_auth.first = auth1.first new_auth.last = auth1.last new_auth.save() for auth2 in orm['post2.author'].objects.all(): new_auth = orm.Author() new_auth.first = auth2.first new_auth.middle = auth2.middle new_auth.last = auth2.last new_auth.save() for tag in orm['post1.tag'].objects.all(): new_tag = orm.Tag() new_tag.name = tag.name new_tag.save() for tag in orm['post2.tag'].objects.all(): new_tag = orm.Tag() new_tag.name = tag.name new_tag.save() for post1 in orm['post1.post'].objects.all(): new_genpost = orm.Post() # Content new_genpost.created_on = post1.created_on new_genpost.title = post1.title new_genpost.content = post1.content # Foreign keys new_genpost.author = orm['genpost.author'].objects.filter(\ first=post1.author.first,last=post1.author.last)[0] new_genpost.save() # Needed for M2M updates for tag in post1.tags.all(): new_genpost.tags.add(\ orm['genpost.tag'].objects.get(name=tag.name)) new_genpost.save() post1.delete() for post2 in orm['post2.post'].objects.all(): new_extpost = p2.ExtPost() new_extpost.created_on = post2.created_on new_extpost.title = post2.title new_extpost.content = post2.content # Foreign keys new_extpost.author_id = orm['genpost.author'].objects.filter(\ first=post2.author.first,\ middle=post2.author.middle,\ last=post2.author.last)[0].id new_extpost.extra_content = post2.extra_content new_extpost.category_id = post2.category_id # M2M fields new_extpost.save() for tag in post2.tags.all(): new_extpost.tags.add(tag.name) # name is primary key new_extpost.save() post2.delete() # Get rid of author and tags in post1 and post2 orm['post1.author'].objects.all().delete() orm['post1.tag'].objects.all().delete() orm['post2.author'].objects.all().delete() orm['post2.tag'].objects.all().delete() def backwards(self, orm): raise RuntimeError("No backwards.")
现在应用这些迁移:
接下来,你可以从post1 / models.py和post2 / models.py中删除现在多余的部分,然后创建schemamigrations以将表更新为新状态:
$./manage.py schemamigration post1 --auto $./manage.py schemamigration post2 --auto $./manage.py migrate
就是这样!希望所有这些都能奏效,并且你已经重构了模型。