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schema-evolution: added documentation
git-svn-id: http://code.djangoproject.com/svn/django/branches/schema-evolution@5737 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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Derek Anderson
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docs/schema-evolution.txt
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262
docs/schema-evolution.txt
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=====================================
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Django Schema Evolution Documentation
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=====================================
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Schema evolution is the function of updating an existing Django generated
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database schema to a newer/modified version based upon a newer/modified set of
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Django models.
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This documentation will take you through several common model changes and show
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you how Django's schema evolution handles them. Each example provides the pre
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and post model source code, as well as the SQL output.
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Adding / Removing Fields
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------------------------
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Model: version 1
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(maxlength=200)
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pub_date = models.DateTimeField('date published')
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author = models.CharField(maxlength=200)
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def __str__(self):
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return self.question
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class Choice(models.Model):
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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votes = models.IntegerField()
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def __str__(self):
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return self.choice
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Model: version 2
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(maxlength=200)
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pub_date = models.DateTimeField('date published')
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author = models.CharField(maxlength=200)
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def __str__(self):
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return self.question
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# new fields
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pub_date2 = models.DateTimeField('date published')
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class Choice(models.Model):
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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votes = models.IntegerField()
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def __str__(self):
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return self.choice
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# new fields
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votes2 = models.IntegerField()
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hasSomething = models.BooleanField()
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creatorIp = models.IPAddressField()
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Output: v1⇒v2
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BEGIN;
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ALTER TABLE `case01_add_field_poll` ADD COLUMN `pub_date2` datetime NOT NULL;
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ALTER TABLE `case01_add_field_choice` ADD COLUMN `votes2` integer NOT NULL;
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ALTER TABLE `case01_add_field_choice` ADD COLUMN `hasSomething` bool NOT NULL;
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ALTER TABLE `case01_add_field_choice` ADD COLUMN `creatorIp` char(15) NOT NULL;
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COMMIT;
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Output: v2⇒v1
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-- warning: as the following may cause data loss, it/they must be run manually
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-- ALTER TABLE `case01_add_field_poll` DROP COLUMN `pub_date2`;
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-- end warning
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-- warning: as the following may cause data loss, it/they must be run manually
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-- ALTER TABLE `case01_add_field_choice` DROP COLUMN `votes2`;
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-- end warning
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-- ALTER TABLE `case01_add_field_choice` DROP COLUMN `creatorIp`;
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-- end warning
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-- ALTER TABLE `case01_add_field_choice` DROP COLUMN `hasSomething`;
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-- end warning
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Renaming Fields
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---------------
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Model: version 1
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from django.db import models
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class Poll(models.Model):
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"""this model originally had fields named pub_date and the_author. you can use
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either a str or a tuple for the aka value. (tuples are used if you have changed
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its name more than once)"""
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question = models.CharField(maxlength=200)
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pub_date = models.DateTimeField('date published', aka='publish_date')
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the_author = models.CharField(maxlength=200, aka='the_author')
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def __str__(self):
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return self.question
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class Choice(models.Model):
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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votes = models.IntegerField(aka='votes')
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def __str__(self):
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return self.choice
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Model: version 2
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from django.db import models
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class Poll(models.Model):
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"""this model originally had fields named pub_date and the_author. you can use
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either a str or a tuple for the aka value. (tuples are used if you have changed
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its name more than once)"""
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question = models.CharField(maxlength=200)
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published_date = models.DateTimeField('date published', aka=('pub_date', 'publish_date'))
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author = models.CharField(maxlength=200, aka='the_author')
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def __str__(self):
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return self.question
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class Choice(models.Model):
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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number_of_votes = models.IntegerField(aka='votes')
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def __str__(self):
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return self.choice
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Output: v1⇒v2
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BEGIN;
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ALTER TABLE `case02_rename_field_poll` CHANGE COLUMN `pub_date` `published_date` datetime NOT NULL;
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ALTER TABLE `case02_rename_field_poll` CHANGE COLUMN `the_author` `author` varchar(200) NOT NULL;
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ALTER TABLE `case02_rename_field_choice` CHANGE COLUMN `votes` `number_of_votes` integer NOT NULL;
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COMMIT;
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Renaming Models
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---------------
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Model: version 1
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(maxlength=200)
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pub_date = models.DateTimeField('date published')
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author = models.CharField(maxlength=200)
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def __str__(self):
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return self.question
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class Choice(models.Model):
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"the original name for this model was 'Choice'"
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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number_of_votes = models.IntegerField()
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def __str__(self):
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return self.choice
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class Meta:
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aka = ('Choice', 'OtherBadName')
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Model: version 2
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(maxlength=200)
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pub_date = models.DateTimeField('date published')
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author = models.CharField(maxlength=200)
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def __str__(self):
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return self.question
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class Option(models.Model):
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"the original name for this model was 'Choice'"
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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# show that field name changes work too
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votes = models.IntegerField(aka='number_of_votes')
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def __str__(self):
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return self.choice
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class Meta:
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aka = ('Choice', 'BadName')
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Output: v1⇒v2
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BEGIN;
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ALTER TABLE `case03_rename_model_choice` RENAME TO `case03_rename_model_option`;
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ALTER TABLE `case03_rename_model_option` CHANGE COLUMN `number_of_votes` `votes` integer NOT NULL;
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COMMIT;
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Changing Flags
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--------------
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Model: version 1
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(maxlength=200)
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pub_date = models.DateTimeField('date published')
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author = models.CharField(maxlength=200)
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def __str__(self):
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return self.question
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class Choice(models.Model):
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"the original name for this model was 'Choice'"
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poll = models.ForeignKey(Poll)
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choice = models.CharField(maxlength=200)
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votes = models.IntegerField()
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def __str__(self):
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return self.choice
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class Foo(models.Model):
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GENDER_CHOICES = (
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('M', 'Male'),
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('F', 'Female'),
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)
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gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)
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Model: version 2
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from django.db import models
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class Poll(models.Model):
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question = models.CharField(maxlength=100)
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pub_date = models.DateTimeField('date published')
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author = models.CharField(maxlength=200)
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def __str__(self):
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return self.question
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class Choice(models.Model):
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"the original name for this model was 'Choice'"
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poll = models.ForeignKey(Poll)
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# make sure aka still works with a flag change
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option = models.CharField(maxlength=400, aka='choice')
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votes = models.IntegerField()
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votes2 = models.IntegerField() # make sure column adds still work
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def __str__(self):
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return self.choice
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class Foo(models.Model):
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GENDER_CHOICES = (
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('M', 'Male'),
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('F', 'Female'),
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)
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gender = models.CharField(maxlength=1, choices=GENDER_CHOICES, db_index=True)
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gender2 = models.CharField(maxlength=1, null=True, unique=True)
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Output: v1⇒v2
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BEGIN;
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ALTER TABLE `case04_change_flag_poll` MODIFY COLUMN `question` varchar(100) NOT NULL;
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ALTER TABLE `case04_change_flag_foo` ADD COLUMN `gender2` varchar(1) NULL UNIQUE;
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ALTER TABLE `case04_change_flag_choice` MODIFY COLUMN `choice` varchar(400) NOT NULL;
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ALTER TABLE `case04_change_flag_choice` CHANGE COLUMN `choice` `option` varchar(400) NOT NULL;
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ALTER TABLE `case04_change_flag_choice` ADD COLUMN `votes2` integer NOT NULL;
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COMMIT;
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Conclusion
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----------
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That's pretty much it. If you can suggest additional examples or test cases you
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think would be of value, please email me at public@kered.org.
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