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POMoving data from one django model to another (django+south) on a living app
 

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  1. POMoving data from one django model to another (django+south) on a living app
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    <p>I'm trying to move some fields from one django model to a new one. Let's assume I've got a book model:</p> <pre><code>class Book(models.Model): title = models.CharField(max_length=128) author = models.CharField(max_length=128) </code></pre> <p>I decided I need a separate model for author (to add extra data etc.). So, bearing in mind that I have a running application filled with data, the desired layout that keeps compatibility would be:</p> <pre><code>class Author(models.Model): name = models.CharField(max_length=128, null=True) # null at first; filled with datamigration nationality = models.CharField(max_length=64, null=True) # we don't have nationality for existing authors, but we'll ask the new ones class Book(models.Model): title = models.CharField(max_length=128) author_model = models.ForeignKey(Author, null=True) @property def author(self): return self.author_model.name @author.setter def author(self, newval): self.author_model.name = newval </code></pre> <p>This way I would have to create schemamigration that adds authors, then a datamigration to transfer the data and fill the author_model_id for books, and finally a datamigration to remove the "author" column from "books" table. The question is, will my migration be valid after changing Book.author from field to property? I mean, if in one of previous migrations South tries to access Book.author (expecting a CharField) it will actually get a property that tries to get nonexistent model. How to do it right?</p>
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