In addition to retrieving a field from a Record, as outlined above in the
Filter section, we sometimes need to refine which fields we want to select.
Or we may want to return a modified version of a field. To do this, we rely on functions.
The syntax for a function is <function name> <open parenthesis> <args>
<close parenthesis>, where <args> represents one or more arguments separated by
commas. An argument may be a string literal (such as
'hello') or a number
literal (such as
48), or could be a relative or absolute RecordPath (such
/id). Additionally, we can use functions
within a filter. For example, we could use a RecordPath such as
isEmpty('name') ]/id to retrieve the
id field of any person
whose name is empty. A listing of functions that are available and their corresponding
documentation can be found below in the Functions section.