user model - id vs pid

[kevinclancy]

Loco's built-in user table has two fields called id and pid.

The id field is the primary key, whereas the pid field is a Uuid. The default user model contains a find_by_pid method.

I understand both of these fields to be unique identifiers for users. Why do we have two different identifier fields? Is the find_by_pid method inefficient considering that no index for the pid field is added in the default users migration?

[kaplanelad]

The app uses two identifiers for different purposes. The id field is an internal primary key, an auto-incrementing integer. The pid field is a UUID meant to be public-facing, for example, in APIs or URLs, because it’s hard to guess and avoids leaking internal information like sequential user counts.

[kevinclancy]

Okay, I think I get it. The uuid makes it difficult to harvest user information, because it cannot be guessed and inserted into urls. It also hides the order in which two distinct users registered, though I don't think anyone would care about keeping that information private.

The integer id seems redundant, then. Couldn't we just use the uuid or the user's email address as the primary key?

I also wonder about find_by_pid function. Without creating an index for the pid column, it's inefficient, isn't it?