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POUsing south to refactor a Django model with inheritance
 

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  1. POUsing south to refactor a Django model with inheritance
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    <p>I was wondering if the following migration is possible with Django <a href="http://south.aeracode.org/" rel="nofollow noreferrer">south</a> and still retain data.</p> <h2>Before:</h2> <p>I currently have two apps, one called tv, one called movies, each with a VideoFile model (simplified here):</p> <p><strong>tv/models.py:</strong></p> <pre><code>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) </code></pre> <p><strong>movies/models.py:</strong></p> <pre><code>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) </code></pre> <h2>After:</h2> <p>Because the two videofile objects are so similar I want to get rid of duplication and create a new model in a separate app called media that contains a generic VideoFile class and use inheritance to extend it:</p> <p><strong>media/models.py:</strong></p> <pre><code>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) </code></pre> <p><strong>tv/models.py:</strong></p> <pre><code>class VideoFile(media.models.VideoFile): show = models.ForeignKey(Show, blank=True, null=True) </code></pre> <p><strong>movies/models.py:</strong></p> <pre><code>class VideoFile(media.models.VideoFile): movie = models.ForeignKey(Movie, blank=True, null=True) </code></pre> <p>So my question is, how can I accomplish this with django-south and still maintain existing data?</p> <p>All three these apps are already managed by south migrations and according to the south documentation it is bad practice to combine a schema and data migration and they recommend it should be done in a few steps.</p> <p>I think it could be done using separate migrations like this (assuming media.VideoFile is already created)</p> <ol> <li>Schema migration to rename all fields in tv.VideoFile and movies.VideoFile that will move to the new media.VideoFile model, maybe to something like old_name, old_size, etc</li> <li>Schema migration to tv.VideoFile and movies.VideoFile to inherit from media.VideoFile</li> <li>Data migration to copy old_name to name, old_size to size, etc</li> <li>Scheme migration to remove old_ fields</li> </ol> <p>Before I go through all that work, do you think that will work? Is there a better way?</p> <p>If you're interested, the project is hosted here: <a href="http://code.google.com/p/medianav/" rel="nofollow noreferrer">http://code.google.com/p/medianav/</a></p>
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