I have a many_to_many table with a migration that looks like this:

    def change do
      create table(:drivers_drivers) do
        add(:child_id, references(:drivers, on_delete: :delete_all), null: false)
        add(:parent_id, references(:drivers, on_delete: :delete_all), null: false)
        add(:position, :integer, null: false)
      end

      create(unique_index(:drivers_drivers, [:parent_id, :child_id], name: "unique_parent_child"))
      create(unique_index(:drivers_drivers, [:parent_id, :position], name: "unique_parent_position"))
    end

This creates indexes in PostgreSQL that look like this:

Indexes:
    "drivers_drivers_pkey" PRIMARY KEY, btree (id)
    "unique_parent_child" UNIQUE, btree (parent_id, child_id)
    "unique_parent_position" UNIQUE, btree (parent_id, "position")

I found that I was unable to reference the unique indexes as a :conflict_target in a call to insert_all/3. I was expecting that I could provide the options on_conflict: :replace_all, conflict_target: {:constraint, :unique_parent_child}, but this results in the error ERROR 42704 (undefined_object): constraint "unique_parent_child" for table "drivers_drivers" does not exist.

I was able to fix this issue by adding the following to the migration:

    execute("""
    ALTER TABLE drivers_drivers 
    ADD CONSTRAINT "unique_parent_child" 
    UNIQUE USING INDEX "unique_parent_child";
    """)
    
    execute("""
    ALTER TABLE drivers_drivers 
    ADD CONSTRAINT "unique_parent_position" 
    UNIQUE USING INDEX "unique_parent_position";
    """)

It feels like I am doing something wrong. Is there a way of referencing indexes in the :conflict_target option without defining them in PostgreSQL as constraints? Or, is there a way of specifying in the migration that an index should also be a constraint, without having to execute SQL?

A supplementary question is how can I specify more than one constraint as the :conflict_target to insert_all? It seems to only accept a tuple, with a single constraint specified as the second element in the tuple.