Hello everyone, when I run my unit test, I sometimes (not all the time) run into this error:
(Postgrex.Error) ERROR 40P01 (deadlock_detected) deadlock detected
hint: See server log for query details. Process 11437 waits for ShareLock on transaction 56033; blocked by process 11436. Process 11436 waits for ShareLock on transaction 56040; blocked by process 11437.
The test attempts to insert 3 records:
work_orders =
for _ <- 1..3 do
{:ok, work_order} = Documents.create_work_order(attrs)
work_order
end
expected_counters = [1, 2, 3]
assert expected_counters == work_orders |> Enum.map(& &1.counter)
create_work_order is an Ecto.Multi that:
- Inserts counter to
countersDB (business requirement dictates that counter restarts from 1 every year) - Grabs the returned counter to insert together to
work_ordersDB - Repo.transaction()
Is the above loop a bad way to test? Or is my transaction function incorrect even though it works (pasted below)?
def create_work_order(attrs \\ %{}) do
counter_changeset = Counter.changeset(%Counter{}, attrs)
work_order_changeset = WorkOrder.creation_changeset(%WorkOrder{}, attrs)
Multi.new()
# Get the next counter of the year
# If year doesn’t yet exist, create one and set counter to 1 (database default)
|> Multi.insert(:next_counter, counter_changeset,
# If year exists, increment the counter by 1
conflict_target: :year,
on_conflict: [inc: [counter: 1]]
)
# Insert work order, with counter added to the changeset
|> Multi.insert(
:work_order,
fn %{next_counter: %{counter: counter}} ->
work_order_changeset
|> Ecto.Changeset.put_change(:counter, counter)
end
)
|> Repo.transaction()
|> case do
{:ok, %{work_order: work_order}} ->
{:ok, work_order}
{:error, :next_counter, _changeset, _changes} ->
# Return work_order_changeset for more thorough field checks
{:error, %{work_order_changeset | action: :insert}}
{:error, :work_order, changeset, _changes} ->
{:error, changeset}
end
end
