Hi! Just stumbled upon this error today and I’m not sure I understand why this is happening - besides, of course, the obvious problem Postgrex is reporting:

Postgrex expected a binary of 16 bytes, got “4c67a49e-fd03-4c1a-9679-713e952ecf73”. Please make sure the value you are passing matches the definition in your table or in your query or convert the value accordingly.

I’m trying to insert a row in a table that has the correct type and is properly migrated:

INSERT INTO "organization_members" ("organization_id","role","user_id") VALUES ($1,$2,$3) [1, "admin", "4c67a49e-fd03-4c1a-9679-713e952ecf73"]

And the migration is:

create table(:organizations_members, primary_key: false) do
  add :organization_id, references(:organizations), primary_key: true
  add :user_id, references(:users, type: :uuid), primary_key: true
  add :role, OrganizationMemberRole.type(), default: "reader"
end

create index(:organizations_members, [:organization_id, :user_id])

And I’m inserting it like this:

insert_membership = fn repo, %{organization: organization} ->
  membership = %{user_id: user.id, organization_id: organization.id, role: "admin"}
  repo.insert_all("organizations_members", [membership])
end

Ecto.Multi.new()
|> Ecto.Multi.insert(:organization, Organization.changeset(%Organization{}, attrs))
|> Ecto.Multi.run(:members, insert_membership)
|> Repo.transaction()
|> case do
  {:ok, %{organization: organization}} -> {:ok, organization}
  {:error, :organization_id, changeset, _} -> {:error, changeset}
  {:error, :members, _, _} -> :error
end

Interestingly enough, if I insert it by hand I don’t have a problem at all, so I guess something is happening when Postgrex is trying to return the query results. Also, the console outputs:

[debug] Query OK db=0.7ms`
rollback []

I think I’ve read somewhere that it would be possible to specify the data types for schemaless operations (or changesets) I don’t remember exactly. So, if someone has a fresh memory on the subject I’d really appreciate the help.