How to do get_or_insert_by in Ecto without race condition?

[silverdr]

@josevalim

If you do insert(data, on_conflict: :nothing, returning: true), it will do nothing if the data exists and return all fields from the database.

As clarified in a separate thread this is not actually true. If the function only translates syntax between Elixir and SQL then only the equivalent SQL behaviour remains valid. PostgreSQL documentation says:

The optional RETURNING clause causes INSERT to compute and return value(s) based on each row actually inserted (or updated, if an ON CONFLICT DO UPDATE clause was used)

This is consistent with results of my quick tests above: on_conflict: :nothing prevents returning fields from the database as no rows are “actually inserted (or updated)”. Shall see if I can improve this section of the docs