let me know if you have this problem.
you want user to enter all the entities and then allow the save button to go to server and do the needful activity, I mean posting the values.
If this is the case, you have two steps :
2. All the three entries are posted to server and checked with the backend if the entry is valid.
Then you know what to do,
if condition true
Let me know if I explained you that you wanted.