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Django ORM misreading PostgreSQL sequences?

Answer 1

+1 A:

Django doesn't hold or directly read the sequence values in any way. I've explained it f.ex. in this question: 2088210/django-object-creation-and-postgres-sequences.

Postgresql does increment the sequence when you try to add a row, even if the result of the operation is not successful (raises a duplicate key error) the sequence incrementation doesn't rollback. So, that's the reason why it works the second time you try adding a row.

I don't know why your sequences are not set properly, could you check what is the sequence value before dump and after restore, and do the same with the max() pk of the table? Maybe it's an 8.1 bug with the restore? I don't know. What I'm sure of: it's not Django's fault.

zalew 2010-07-05 02:27:10

I wish I understood why, but this appears to be the answer. I had only one auth group, and the dump sets the current value of that ID's sequence to 1: `SELECT pg_catalog.setval('auth_group_id_seq', 1, false);`. If I try selecting the nextval from that sequence it's also 1. The subsequent query for nextval bumps the sequence to 2.

bennylope 2010-07-08 01:09:34

@zalew: That is incorrect; Django does in fact fetch values from PostgreSQL sequences. If you enable logging of all statements in your DB, you'll see that Django issues quite a few `SELECT CURRVAL('"app_table_id_seq"');` commands. In fact, if you look at the code for `django.db.models.sql.compiler.SQLInsertCompiler.execute_sql()` and `django.db.backends.postgresql.operations.DatabaseOperations.last_insert_id()`, youll see that it fetches the sequence value after every single INSERT command unless `autocommit=True`.

Aram Dulyan 2010-07-18 06:44:29

Answer 2

+1 A:

I am guessing that your sequence is out of date.

You can fix that like this:

select setval('app_model_id_seq', max(id)) from app_model;

WoLpH 2010-07-05 02:37:40

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