Assign without creating other elements

[sdiemert]

Right now it appears that the (assign ...) operator requires that it be incorporated into a pattern that also creates other nodes/edges.

For example,

(rule 'create-person! ['p]
  :create 
   (pattern 
    (node :label "Person" :asserts {:name "'&p'"})))

(rule 'change-name! ['x 'y]
      :read (pattern (node 'n :label "Person" :asserts {:name "'&x'"}))
      :create (pattern 
               (assign "n.name='&y'")))

(clear!)

(create-person! "Simon")
(-> any? matches view)

(change-name! "Simon" "Bob")
(-> any? matches view)

Does not have the desired effect. It fails to do the assignment of Simon -> Bob.

However, if I add a DONT_CARE node to the create pattern then it works as desired.

(rule 'create-person! ['p]
  :create 
   (pattern 
    (node :label "Person" :asserts {:name "'&p'"})))

(rule 'change-name! ['x 'y]
      :read (pattern (node 'n :label "Person" :asserts {:name "'&x'"}))
      :create (pattern 
               (node :label "DONT_CARE")
               (assign "n.name='&y'")))

[sdiemert]

This can be mitigated for now using the :merge true option on the DONT_CARE nodes (so you only ever have one of these... but it still isn't ideal in my view.

[jenshweber]

I am going to revisit this part in context of the next major release of Grape.

[jenshweber]

Since the new version of Grape (GrapeVine) no longer has assignments (since it is functional), I am closing this issue.