Ecto Sandbox: foreign_key_constraint error only in unit test

Question

I'm new to Elixir, so I'm having trouble nailing this down. If you want to see additional files let me know - I don't know yet what's important or not to include.

I have an "Account" object that has many "User" objects. I'm trying to update a user with the associated account using Ecto.Changset.cast_assoc. It works fine from iEx, but in the unit test, I get:

(Ecto.ConstraintError) constraint error when attempting to update struct:
* users_account_id_fkey (foreign_key_constraint)

Now, I know this has something to do with the Ecto Sandbox, but I can't figure out how to write the test so that it works. I could just move on and not write this test, but I want to understand how to make it work for the future.

In my project, I have a Test Helper that looks like so (just setting up third party apps):

ExUnit.start()

{:ok, _} = Application.ensure_all_started(:wallaby)
{:ok, _} = Application.ensure_all_started(:ex_machina)
Faker.start()

Application.put_env(:wallaby, :base_url, BondiWeb.Endpoint.url())

I also have standard channel_case, conn_case, data_case and I haven't changed those. Finally, my test.exs is pointing to the sandbox adapter:

pool: Ecto.Adapters.SQL.Sandbox

I've tried several variations of the different sandbox modes (:auto, :manual, :shared) but can't seem to figure out how to setup this test so that both records can be inserted and the test passes.

I suspect it has something to do with my uses ExMachina to manage my fixtures, and that I'm "doing it wrong". But I also tried to create the user directly, without using ExMachina and that didn't seem to work either.

How do I write a test that can make multiple associated saves to the sandbox, and have them remain until the end of the test?

Just to be sure, can you try to run mix ecto.reset, both with and without MIX_ENV=test? When you run iex, you are by default in the dev mix env, while tests run in the test env, both using a different database. This might explain a difference in behaviour as well. — sabiwara
the error most likely tells that you are trying to update to a foreign key that doesn't exist — Daniel
Like @sabiwara said: make sure you run MIX_ENV=test mix ecto.migrate (or do the full drop, create, migrate reset) to ensure that your test database is in the shape that your tests expect it to be in. — Everett

Dave Sanders Dave Sanders · Accepted Answer · 2020-09-22T14:56:51

Thanks to everyone who commented. It does appear that it was related to the test DB not being dropped / recreated. I swear I did that, but I guess not!

For the record I did:

MIX_ENV=test mix ecto.reset

reran the test, and it worked.

Ecto Sandbox: foreign_key_constraint error only in unit test

1 Answers