pgClassExpression

A pgClassExpression represents the value of an SQL expression extracted from a pgSelectSingle, pgUnionAllSingle or similar step.

You won't construct a pgClassExpression directly, normally you'll get it from $pgSelectSingle.select(...), resource.execute(...) or similar methods.

pgClassExpression.get(attr)

The most commonly used method on a pgClassExpression, this gets a step representing the value of the given attribute from the expression; only applicable when the expression represents a composite type.

Not opaque

Unlike a pgSelectSingle, a pgClassExpression is not opaque, so it's fine to use it directly as a dependency of any other step.