The primary key type of the five schemas in StatifierRouter.Schema: the id of a row, whatever type the host's migration gave it.

StatifierRouter.Migrations.up/1 builds id as the host repo's implicit primary key - a bigserial unless the repo's :migration_primary_key says otherwise - or, under its :primary_key option, as the type and default the host names, a text id for instance. The database fills the column in either way, and a schema reads it back as the database holds it: an integer from an integer column, a string from a text column. The package never makes up an id itself and never compares one to anything but another id of the same table.

Casting is exactly Ecto's own :id type: an integer casts to itself, a string that spells one casts to that integer ("42" to 42), and any other string is refused, so a cast that worked or failed under the default key works or fails the same way. A text id is therefore never cast: a host on a text key looks a row up with a where clause that binds the id uncast, where: fragment("? = ?", a.id, ^id), rather than with Repo.get/2 or a changeset cast. The package's own reads bind ids that way too: they never cast an id.

A refused cast names this type rather than :id, as it has since 0.8.0 put the four schemas on it. A changeset error's metadata reads type: StatifierRouter.Schema.Id where it read type: :id, and an Ecto.Query.CastError says the value "cannot be cast to type StatifierRouter.Schema.Id" where it said "cannot be cast to type :id". The values refused are the same; only a host that matches on the metadata's :type or on the message text sees the difference.