sequences

[eriktelepovsky]

trafficstars

Hi. Does it also rename sequences?

[alexei]

I'm not sure I understand. Could you please provide more info?

[eriktelepovsky]

Let's say I have a model old_app.ModelA. Its primary key id points to sequence old_app_modela_id_seq.

localhost=# \d old_app_modela;
                                      Table "public.old_app_modela"
     Column      |           Type           |                             Modifiers                             
-----------------+--------------------------+-------------------------------------------------------------------
 id              | integer                  | not null default nextval('old_app_modela_id_seq'::regclass)

I decide to move it to new_app. So the next value of primary key should still refer to same sequence, but it should be renamed to new_app_modela_id_seq, like this:

localhost=# \d new_app_modela;
                                      Table "public.new_app_modela"
     Column      |           Type           |                             Modifiers                             
-----------------+--------------------------+-------------------------------------------------------------------
 id              | integer                  | not null default nextval('new_app_modela_id_seq'::regclass)

Basically, it should be done with statement:

ALTER SEQUENCE old_app_modela_id_seq RENAME TO new_app_modela_id_seq;

[alexei]

I see. No, it doesn't. Should it?

[eriktelepovsky]

I think yes, it is convenient and more human readable.

Check this out, it may help you: http://marcela-campo.blogspot.sk/2015/01/django-migrations-moving-django-model.html

[alexei]

Thanks for the link. I read that article before implementing this. It doesn't account for other DB engines. For example, SQLite stores sequence information inside a sqlite_sequence table and ALTER SEQUENCE will raise a syntax error. There's also MySQL, Oracle, SQL Server, DB2, Firebird etc.

TBH, the scope of this project is to automate the method described at https://stackoverflow.com/a/30613732/1639699 and, while I understand and agree to the reasoning, renaming sequences seems beyond that.

[alexei]

Ideally renaming a sequence would be implemented as a db operation. Those, however, are not documented and currently I'm not sure how to do that.

[alexei]

One way to implement an operation would be to simply inherit either RunPython or RunSQL and run the appropriate query (or do nothing?) depending on the engine.