Sometimes it is not enough to fetch the data as-is, but it is necessary to add something extra to it. This can be done by adding a computable field to the shape. Let's fetch all text posts and how long they are:
We can even incorporate a comparison to the average post
length in our computable. There are several ways to do
this, so in this example we'll use a DETACHED
construct to denote that the Text we're referring to
in the subquery is supposed to be treated as the
original unmodified set in the database rather than the
object we're adding the data to:
