Question

I created the models in a Django app using manage.py inspectdb on an
existing postgres database. This seemed to work except that all the
primary keys were described in the models as IntegerFields, which made
them editable in the admin panel, and had to be hand-entered based on
knowledge of the id of the previous record. I just learned about this
after some usage by the client, so I went back to change things like

blog_id = models.IntegerField(primary_key=True)

…to…

blog_id = models.AutoField(primary_key=True)

Now the id fields don’t appear in the admin panel (good), but adding new rows
has become impossible (not good).

IntegrityError at /admin/franklins_app/blog/add/

duplicate key value violates unique constraint "blog_pkey"

What’s the fix? (Bonus question: is it possible to capture the value that Django is trying to assign as the primary key for the new row?)

Answer 1

The sequence behind the serial field which is your primary key doesn’t know about the manually entered records.

Find the maximum value of the primary key:

SELECT MAX(<primary_key>) FROM <your_table>;

Then set the next value of the underlying sequence to a number greater than that:

SELECT SETVAL('<primary_key_seq>', <max_value_in_primary_key_plus_something_for_safety>);

You’ll find the name of the sequence (mentioned above as <primary_key_seq>) using:

SELECT pg_get_serial_sequence('<your_table_name>', '<primary_key_column_name');