wpf mvvm save in different table based on choose combobox

hello to all, 

I could not find a suitable solution to my final goal. 

are in a scenery MVVM. 

I have a window (the one for inserting bills) in this window is a combobox where I can choose the types of invoice (invoice immediate, deferred invoice, transport document, quotation, delivery order etc ...) 

and I'll have the respective tables in the db (head and body). 

Now I do based on your choice I can save the data in the related tables. I was not able to implement it in my WPF MVVM solution entity framework code first.

= (And for a few months but to no avail. I do for now to work around this problem, I used automapper ie before the rescue and did the mapping table. 

I put a link to a video of what I would like to replicate on wpf. 

video 

I'm hoping for some help.