NSDerivedAttributeDescription

A description of an attribute that derives its value by performing a calculation on a related attribute.

Declaration

class NSDerivedAttributeDescription

Use derived attributes to optimize fetch performance; for example:

Create a derived searchName attribute to reflect a name attribute with case and diacritics removed for more efficient comparison.
Create a derived relationshipCount attribute to reflect the number of objects in a relationship and avoid having to do a join.

Derived attributes support the following expressions:

Expression	Description	Example
to-one keypath	A single value to replicate.	`name` or `author.name`
to-one keypath with a function	The result of calling a function on a single value. [Image] Supported functions include `canonical:`, `uppercase:`, and `lowercase:`. [Image] The `canonical:` function returns a case- and diacritic-insensitive String value.	`canonical:(name)`
to-many keypath with a function	The result of calling an aggregate function on a set of values. [Image] Supported functions include `@count` and `@sum`.	`friends.@count`
time	The current time.	`now()`