I´ve was working around with this but I´m not getting the same result as using the properties. So here are some questions. Supouse Ive got BOParent and BOChild.

    Private Sub BOChild_ParentFormLoading() Handles BoEmpresa1.ParentFormLoading
        ...

        BOParent.RegisterForeignKey(BOchild, "ChildFKFieldname")

....
    End Sub

I was working around with this and there ares somethings I ´m not sure. Actually it does´t work as I espect.

Sopouse I´ve got a BOparent and a BOChild

    Private Sub BoParent_ParentFormLoading() Handles BoParent1.ParentFormLoading
        ...
        BoParent1.RegisterForeignKey(BOchild, "ChildFKFieldname")

       ...

    End Sub

Is this correct. Or I have to put this in the BO instead of the instance of it?

I have to use the method of the parent or the child's one.

That's all

Regards

and, the method is correct? or there is something better.

It looks as though you are going about this correctly, but the code snippet you gave doesn't show the whole picture.  But in short, if your foreign keys are getting updated, then you are in good shape.