+
+;;;; ** has-a
+
+(defattribute has-a ()
+ ()
+ (:default-properties
+ :has-a nil))
+
+(define-layered-method attribute-value (object (attribute has-a))
+ (meta-model:explode-foreign-key object (slot-name attribute) :nilp t))
+
+(defdisplay ((attribute has-a) object)
+ (let ((args (plist-union (description.properties attribute) (has-a attribute)))
+ (val (attribute-value object attribute)))
+ (when val
+ (setf (getf args :type)
+ 'lol::one-line))
+ (apply #'display* val
+ args)))
+
+