Question

I’m trying to inject sample data into my database, and have created a fixture file that builds my model, and then merges the instance into the database. I’m using merge, because I want to be able to re-run the fixture without recreating the database, or truncating all my tables.

However, upon inspection of my Postgres table’s sequence on primary key, my_items_id_seq shows the following after injecting 10 items:

       Sequence "public.my_items_id_seq"
    Column     |  Type   |        Value        
---------------+---------+---------------------
 sequence_name | name    | my_items_id_seq
 last_value    | bigint  | 1
 start_value   | bigint  | 1
 increment_by  | bigint  | 1
 max_value     | bigint  | 9223372036854775807
 min_value     | bigint  | 1
 cache_value   | bigint  | 1
 log_cnt       | bigint  | 0
 is_cycled     | boolean | f
 is_called     | boolean | t

How can I increase the last_value as I merge in fixture data?

[edit]

The outstanding issue here is that after injecting the data, I can’t add items to the database without getting an IntegrityError from SqlAlchemy. This is due to PostgreSQL trying to insert my new instance with id 1.

Answer 1

The first part of the answer came through reading a link about Django and PostgreSQL, where the author similarly attempted to feed migration data with indexes.

His solution was to grab the highest index, and then execute the following query:

alter sequence profile_billingaddress_id_seq restart with {id};

Through this, I discovered the proper keyword to the PostgreSQL documentation on Sequence Manipulation Functions. The preferred way to do this is to issue this query:

select setval('my_items_id_seq', {id})

… where {id} is obviously a placeholder for a real integer. It also came to my attention that last_value is just the last response from next_value. This is important because using setval instead of the alter sequence business above ensures that nextval provides an unused index. I.e. when using setval where id=10, nextval will return 11. When using the alter sequence command, if id=10, then nextval will also return 10.