anchor.diff:                                  :set ',*jdoc* '$2 'valid-from (:transaction-timestamp)
                                   :where (:= ',*id* '$1)
                                   :returning ',*id*))
  -            :single!)))
  +            :single)))
   
   (defun make-get$ (model table)
     (setf (lookup-query model 'get$)
  
positive.code:                                                       'valid-from
                                                        ',*jdoc*
                                                        :from ,table
                                                        :where (:= ',*id* '$1))
                                               :returning ',*id*)))))
  
  (defun make-update$ (model table)
    (setf (lookup-query model 'update$)
  
negative.code: (in-package :postgres-json)
  
  ;;;; Query management
  
  (defparameter *query-functions* (make-hash-table :test #'equal))
  
  