Method: (MAYBE-UPDATE-SCHEMAS SCHEMA-TABLE T)

Source

(defmethod maybe-update-schemas ((table schema-table) class)
  ;; Rucksack analyzes the new class definition; if it's different from the
  ;; previous version, a new schema is added to the schema table.  From that
  ;; moment, when an instance of the redefined class is created it will be
  ;; saved with the new schema id.
  ;; This is called by the FINALIZE-INHERITANCE method for PERSISTENT-CLASS.
  (let ((slots (mapcar #'slot-definition-name (class-persistent-slots class)))
        (old-schema (find-schema-for-class table class)))
    (if (null old-schema)
        ;; There is no schema yet: create the first one.
        (create-schema table class 0 slots)
      ;; There is a schema already: create a new one if necessary.
      (when (set-difference slots (persistent-slot-names old-schema))
        ;; Add a new schema for this class.
        (create-schema table class (1+ (schema-version old-schema)) slots)
        ;; Mark all older versions as obsolete and compute their
        ;; slot diffs w.r.t. to the new schema
        (dolist (schema (old-schemas-for-class table class))
          (let ((old-slots (persistent-slot-names schema)))
            (setf (schema-obsolete-p schema) t
                  (added-slot-names schema) (set-difference slots old-slots)
                  (discarded-slot-names schema) (set-difference old-slots slots))))))))