What is the best approach to change primary keys in an existing Django app?

Question

I have an application which is in BETA mode. The model of this app has some classes with an explicit primary_key. As a consequence Django use the fields and doesn\'t create

Answer 1

I managed to do this with django 1.10.4 migrations and mysql 5.5, but it wasn't easy.

I had a varchar primary key with several foreign keys. I added an id field, migrated data and foreign keys. This is how:

1. Adding future primary key field. I added an id = models.IntegerField(default=0) field to my main model and generated an auto migration.

2. Simple data migration to generate new primary keys:

   def fill_ids(apps, schema_editor):
      Model = apps.get_model('', '')
      for id, code in enumerate(Model.objects.all()):
          code.id = id + 1
          code.save()
   
   class Migration(migrations.Migration):
       dependencies = […]
       operations = [migrations.RunPython(fill_ids)]
   

3. Migrating existing foreign keys. I wrote a combined migration:

   def change_model_fks(apps, schema_editor):
       Model = apps.get_model('', '')  # Our model we want to change primary key for
       FkModel = apps.get_model('', '')  # Other model that references first one via foreign key
   
       mapping = {}
       for model in Model.objects.all():
           mapping[model.old_pk_field] = model.id  # map old primary keys to new
   
       for fk_model in FkModel.objects.all():
           if fk_model.model_id:
               fk_model.model_id = mapping[fk_model.model_id]  # change the reference
               fk_model.save()
   
   class Migration(migrations.Migration):
       dependencies = […]
       operations = [
           # drop foreign key constraint
           migrations.AlterField(
               model_name='',
               name='model',
               field=models.ForeignKey('', blank=True, null=True, db_constraint=False)
           ),
   
           # change references
           migrations.RunPython(change_model_fks),
   
           # change field from varchar to integer, drop index
           migrations.AlterField(
               model_name='',
               name='model',
               field=models.IntegerField('', blank=True, null=True)
           ),
       ]
   

4. Swapping primary keys and restoring foreign keys. Again, a custom migration. I auto-generated the base for this migration when I a) removed primary_key=True from the old primary key and b) removed id field

   class Migration(migrations.Migration):
       dependencies = […]
       operations = [
           # Drop old primary key
           migrations.AlterField(
               model_name='',
               name='',
               field=models.CharField(max_length=100),
           ),
   
           # Create new primary key
           migrations.RunSQL(
               ['ALTER TABLE  CHANGE id id INT (11) NOT NULL PRIMARY KEY AUTO_INCREMENT'],
               ['ALTER TABLE  CHANGE id id INT (11) NULL',
                'ALTER TABLE  DROP PRIMARY KEY'],
               state_operations=[migrations.AlterField(
                   model_name='',
                   name='id',
                   field=models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID'),
               )]
           ),
   
           # Recreate foreign key constraints
           migrations.AlterField(
               model_name='',
               name='model',
               field=models.ForeignKey(blank=True, null=True, to='.'),
       ]
   
   
       
   
                
   
                                                           
               
               
   
                 
                   
                   0
                 
                      
                   
                  讨论(0)
                 
                                                     
                 
                 
   
                             
                
          
             
                 
                                          
   
        查看其它8个回答
   
   
               
                            
   
                       
   
   
   
                  
               
   
       发布评论:
       
   
            
                           
       
       
   提交评论 
     
     
   
                       
                       
   
                       
   
                           
   
                           
                            加载中...
                           
                       
                   
             
                                 			
           
           
           
   
             
   
               
               
   
                 
                 
   
               
       
   
   
                                    
                 
               
                             
       
   
           
            
   
                   验证码
                   
   
                     
                   
                   
   
                      看不清?
                   
                 
                                     
   
                       
      
                    
                
                 
   提交回复
               
             
           
         
          
         
       
       
   
             
    
        
    
   
           
   热议问题