@key annotation
The @key annotation is used
to specify key attributes for entities and relations.
Syntax
<type label> owns <attribute type label> @key;The @key annotation does not accept any arguments.
Usage
The @key annotation is used to mark an owned attribute as a key, which in fact declares two constraints:
-
The unique constraint as an equivalent of
@unique. -
The cardinality constraint as an equivalent of
@card(1).
For example, the following statement declares that any content should have exactly one key id with a unique (across all content s) value:
define
entity content owns id @key;
attribute id value string;Subtyping
Refer to unique constraint subtyping and card constraint subtyping for the respective constraints' subtyping behavior.
Limitations
Cannot be used with the @unique annotation the @card annotation as it produces same constraints.
See unique annotation supported value types for the list of supported value types.