title: save correct value type
body: <p>i have a textfield where the user should enter a price like 20,00
  this value i would like to save into core data. i chose the attribute type double - i hope this is correct.</p>
  
  <p>if i request the data and show it as print result, i get this output:
  20.0</p>
  
  <p>but i need 20.00
  and later i can change the "." to ",".
  how can I get the second missing null?</p>