Upsert_all with uniqueness index constraint

I'm facing a dilemma.

I've created a model with an wave_order column with uniqueness db index with wavable. wavable is a polymorphic (but we don't care actually).

# migration
create_table :invitation_waves do |t|
  t.string :name, null: false
  t.references :wavable, polymorphic: true, index: true
  t.integer :wave_order, null: false
  t.timestamps
end
add_index :invitation_waves, [:wavable_id, :wavable_type, :wave_order], unique: true

# This first time, it's working
InvitationWave.upsert_all([{id: 1, name: "Wave1", wave_order: 0, wavable_id: my_object.id, wavable_class: my_object.class.name}, {id: 2, name: "Wave2", wave_order: 1, wavable_id: my_object.id, wavable_class: my_object.class.name}], unique_by: :id, update_only: :wave_order, record_timestamps: true)

# The second time, it's not because of the db constraint. 
InvitationWave.upsert_all([{id: 1, name: "Wave1", wave_order: 1, wavable_id: my_object.id, wavable_class: my_object.class.name}, {id: 2, name: "Wave2", wave_order: 2, wavable_id: my_object.id, wavable_class: my_object.class.name}], unique_by: :id, update_only: :wave_order, record_timestamps: true)

# => ActiveRecord::RecordNotUnique:
       PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "idx_on_wavable_id_wavable_type_wave_order_39aa14a122"
       DETAIL:  Key (wavable_id, wavable_type, wave_order)=(1, MyObject, 1) already exists.

Is there any other solution than those 3:

1. Remove the db index uniqueness
2. Update manually each row
3. Use twice the upsert_all (first time with wrong but available wave_orders, second time with correct wave_orders

What's about adding DEFERRABLE INITIALLY IMMEDIATE for your uniqueness constraint?

In this case PostgreSQL checks uniqueness before commitment

def up
  create_table :invitation_waves do |t|
    t.string :name, null: false
    t.references :wavable, polymorphic: true, index: true
    t.integer :wave_order, null: false
    t.timestamps
  end

  execute <<~SQL.squish
    ALTER TABLE invitation_waves
    ADD CONSTRAINT idx_on_wavable_id_wavable_type_wave_order
    UNIQUE (wavable_id, wavable_type, wave_order)
    DEFERRABLE INITIALLY IMMEDIATE
  SQL
end

def down
  drop_table :invitation_waves
end

In new versions of Rails you can apply migration method unique_constraint

create_table :invitation_waves do |t|
  t.string :name, null: false
  t.references :wavable, polymorphic: true, index: true   t.integer :wave_order, null: false
  t.timestamps
  t.unique_constraint %i[wavable_id wavable_type wave_order], deferrable: :immediate
end

or add_unique_constraint

add_unique_constraint :invitation_waves, %i[wavable_id wavable_type wave_order], deferrable: :immediate

No matter how you add this constraint it will work such way

# First query (populate records)
InvitationWave.upsert_all(
  [
    {id: 1, name: "Wave1", wave_order: 0, wavable_id: 1, wavable_type: "MyObject"},
    {id: 2, name: "Wave2", wave_order: 1, wavable_id: 1, wavable_type: "MyObject"}
  ],
  unique_by: :id, update_only: :wave_order, record_timestamps: true
)

# Second query (update records) that failed without DEFERRABLE, but now is ok
InvitationWave.upsert_all(
  [
    {id: 1, name: "Wave1", wave_order: 1, wavable_id: 1, wavable_type: "MyObject"},
    {id: 2, name: "Wave2", wave_order: 2, wavable_id: 1, wavable_type: "MyObject"}
  ],
  unique_by: :id, update_only: :wave_order, record_timestamps: true
)

Both queries will be successful because constraint will be checked at the end of the statement (immediately before commit)

But when you try to execute third query,

# Will fail, because there is other record with same wave_order
InvitationWave.find(2).update!(wave_order: 1)

it will fail because of UNIQUE constraint