Sometimes dropping the primary key isn't desired

[geofflane]

Found this problem using params_for, etc.

defp drop_ecto_fields(record = %{__struct__: struct, __meta__: %{__struct__: Ecto.Schema.Metadata}}) do
    ...
    |> Map.drop(struct.__schema__(:primary_key))

In the simple case the primary key is a synthetic id that is auto-generated by the database. In the not so simple case, you have overridden the primary key so that it's not auto-generated by the database. It could be a business key that is meaningful. It could be a one-to-one mapping where the primary key is a foreign key reference to another table.

e.g.

# This has a normal auto-incrementing ID
schema "plays" do
  has_one :scoring
end

# This is a one-to-one modeled in the database by having the PK be a FK to the plays.id column.
@primary_key {:play_id, :integer, []}
schema "scoring" do
  field :type, :string
  field :points, :integer

  belongs_to :play, MyApp.Play, define_field: false, references: :id
  belongs_to :team, MyApp.Team, references: :id
end

In the latter case, the primary key is also a foreign key reference to another table and is a required field, so using params_for and friends creates invalid params since it drops the PK.

[geofflane]

Maybe only remove autogenerated ids? It looks like that can be done using __schema__(: autogenerate_id)