Ecto.Adapter.Queryable.prepare

You're seeing just the callback prepare, go back to Ecto.Adapter.Queryable module for more information.

Specs

prepare(atom :: :all | :update_all | :delete_all, query :: Ecto.Query.t()) ::
  {:cache, prepared()} | {:nocache, prepared()}

Commands invoked to prepare a query.

It is used on Ecto.Repo.all/2, Ecto.Repo.update_all/3, and Ecto.Repo.delete_all/2. If returns a tuple, saying if this query can be cached or not, and the prepared query. The prepared query is any term that will be passed to the adapter's execute/5.