How to extend Project Task in the Purchase Order header?

Hi everybody,

I am facing a problem I am sure is not so hard, but I cannot find my way through it.

So, my objective is to extend the Purchase Order Header with the Project Task ID.

I created the extension field first, as below:

But I just cannot find how to populate it automatically from the data in the Project Task field.

I tried a Relation in a BO extension going through the AccountingBlockAssignement, but it seems to not be functional.

I also tried to make a Reference to the extension field and created an Event After Modify like:

this.projecttaskpo = this.ExtensionForPO.content

The Project Task PO is my reference to the extension field created in the Cloud Solution.

And the ExtensionForPO is my relation to the TaskID:

import AP.Common.GDT;

import AP.Purchasing.Global as Purchasing;

import AP.ProjectManagement.Global as ProjectManagement;

import AP.IS.CodingBlock.Global as Coding;

[Extension] businessobject AP.Purchasing.Global:PurchaseOrder {

  [Relation(Coding:AccountingCodingBlockDistribution.AccountingCodingBlockAssignment.ProjectTaskKey.TaskID)]

  [Label("Project ID")] element ExtensionForPO : TaskID;

    node Item {

       }

}

I am pretty sure this is not so hard, but I can't figure how to do it.

The Task ID is in the Line Item so I do not understand why it could be so hard to add it in the Purchase Order Header.

Moreover, when I try to make the path directly from the PurchaseOrder, like:

PurchaseOrder.Item.ItemAccountingCodingBlockDistribution.AccountingCodingBlockAssignment.ProjectTaskKey.TaskID

It returns to me that the association between Item and ItemAccountingCodingBlockDistribution is not a node. I know that, but it would be perfect if I could directly go from the Purchase Order BO to the Project Reference and the Project Tasks. But I cannot do that.

Any help on this would be greatly appreciated as it is quite a recurring request from customers.

I could have a misunderstanding in the process of doing it, or even in the code as I am a pure development newbie, so I m open to all propositions.

Thank you all.

Have a nice day.

Jacques-Antoine