[API Request] conditionnal add: on MooseAbstractGroup (and FMSlotMultivalueLink)

[alkalinan]

In his current API implementation, the Moose API for MooseModel and MooseGroup does not let us add an entity and check if another instance is already inside its entity storage.

Current behavior

myMooseModel := MooseModel new. 
"assuming that MyMooseObj has an id attribute"

myMooseModel 
       add: (MyMooseObj new id: 555; name: 'Foo'; yourself).
myMooseModel entities." an OrderedCollection(a GLHProject #Foo)"

myMooseModel 
       addAll: {(MyMooseObj new id: 555; name: 'Foo'; yourself). (MyMooseObj new id: 444; name: 'Bar'; yourself) }.
myMooseModel entities." an OrderedCollection(a MyMooseObj #Foo a MyMooseObj #Foo a MyMooseObj #Bar)" 

Proposed API

myMooseModel := MooseModel new. 

myMooseModel 
       add: (MyMooseObj new id: 555; name: 'Foo'; yourself).
myMooseModel entities." an OrderedCollection(a GLHProject #Foo)"

"add:unless:"
myMooseModel 
   addAll: {(MyMooseObj new id: 555; name: 'Foo'; yourself). (MyMooseObj new id: 444; name: 'Bar'; yourself) } 
   unless: [:existing : new | existing id = new id].
myMooseModel entities." an OrderedCollection(a MyMooseObj #Foo a MyMooseObj #Bar)"

The implementation of add:unless: and addAll:unless: are available in this repository.

This API could also be implemented for FMSlotMultivalueLink like in the following extension