South is absolutely brilliant. I never expected it to properly convert over my data as easily as it did. Basically, I originally had a monolithic table, which I wanted to convert into 3 separate tables linked together using a ForeignKey. The reason was, that 2 fields contains mostly the same information, and re-typing it, and organizing the data was becoming a tad tedious. Here is the first Python script I ran after creating the new tables. This script automatically separates the data into the required tables for me:
from tickets.models import Taxonomy, Category, Reason
print "Starting Taxonomy migration process..."
for tax in Taxonomy.objects.all():
print "Processing %s..." % tax
try:
ci = Category.objects.get(title=tax.ci)
except Category.DoesNotExist:
ci = Category.objects.create(title=tax.ci)
print "Created Category %s." % ci
try:
r = Reason.objects.get(title=tax.reason)
except Reason.DoesNotExist:
r = Reason.objects.create(title=tax.reason)
print "Created Reason %s." % r
tax.ci = ci.pk
tax.reason = r.pk
tax.save()
print "Linked PKs, finished."
As you can see, it replaces the actual category name and reason with just the PK, at first I wasn't sure what South would do with the data if I just convert a CharField over to a ForeignKey. Here are the changes to the main model:
ci = models.CharField(max_length=90, blank=True, verbose_name='CI Unique ID')
reason = models.CharField(max_length=90)
# To:
ci = models.ForeignKey(Category, blank=True, verbose_name='CI Unique ID')
reason = models.ForeignKey(Reason)
Here is the migration data generated by South:
class Migration(SchemaMigration):
def forwards(self, orm):
# Renaming column for 'Taxonomy.ci' to match new field type.
db.rename_column('tickets_taxonomy', 'ci', 'ci_id')
# Changing field 'Taxonomy.ci'
db.alter_column('tickets_taxonomy', 'ci_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['tickets.Category']))
# Adding index on 'Taxonomy', fields ['ci']
db.create_index('tickets_taxonomy', ['ci_id'])
# Renaming column for 'Taxonomy.reason' to match new field type.
db.rename_column('tickets_taxonomy', 'reason', 'reason_id')
# Changing field 'Taxonomy.reason'
db.alter_column('tickets_taxonomy', 'reason_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['tickets.Reason'], max_length=90))
# Adding index on 'Taxonomy', fields ['reason']
db.create_index('tickets_taxonomy', ['reason_id'])
All in all, there was almost no work required, besides writing up a quick Python script to move the actual data to a new table, and place the PK into it. According to the database, the fields are now INTs, as they should be for ForeignKeys.
Foreign Keys are not pointers and need not be integers. In many correctly designed schemas, they probably will not be integers.
South's all well and good until you need to use custom SQL.