mks - Item field constraint based on children field values -

i create constraint on item based on linked child items.

i have item called "project" have child items of "task". both of these items types have state field , same values like, "in progress", "ready review", "complete", etc. want keep user changing "project"/parent item state next state if "task"/child items not in right or same state. once tasks set right state allow project item state advanced. so, possible, , if point me right docs?

visual example:

(t1)

 project state:in progress       children:            task 1 state:in progress            task 2 state:in progress 

(t2) - note @ time user not able change project state next state because tasks not completed.

project state:in progress      children:            task 1 state:ready review            task 2 state:in progress 

(t3)

 project state:in progress       children:            task 1 state:completed            task 2 state:ready review 

(t4) - user can move project item state completed because children in correct state.

 project state:in progress       children:            task 1 state:completed            task 2 state:completed 

(t5)

 project state:completed       children:            task 1 state:completed            task 2 state:completed 

as far know not possible through constraint,you may need custom rule based trigger functionality.

the event trigger (type = project , state !=state[old value] , state[old value]=in progress , state[new value]=completed )

what trigger do? checks state of child tasks , if of child task not completed pop message saying "all child task should completed before moving project completed state"