Defining a Hidden Form Field

First, define a hidden form field that uses a default expression to call the Java class by not including any Display class in the field definition:

<Field name=’jobGrade’>
   <Default>
      <invoke name=’getJobGrade’ class=’com.waveset.custom.DatabaseAccessor’>
         <ref>waveset.accountId</ref>
      </invoke>
   </Default>
</Field>
     </Derivation>

Default expressions are evaluated only if the view does not contain a value for the attribute jobGrade. Once the default expression has been run, the result is stored in jobGrade, and the expression is not run again.