Creating the Trigger

Listing 4.42 defines the trigger to validate timecards. It illustrates a best practice for trigger development: Keep the trigger’s code block as small as possible. Place code in a separate class for easier maintenance and to encourage code reuse. Use naming conventions to indicate that the code is invoked from a trigger, such as the Manager suffix on the class name and the handle prefix on the method name.

Listing 4.42 Trigger validateTimecard

Click here to view code image

trigger validateTimecard on Timecard__c(before insert, before update) {
  TimecardManager.handleTimecardChange(Trigger.old, Trigger.new);
}

To create this trigger, select File, New, Apex Trigger. Enter the trigger name, select the object (Timecard__c), enable the two trigger operations (before insert, before update), and click the Finish button. This creates the trigger declaration and adds it to your project. It is now ready to be filled with the Apex code in Listing 4.42. If you save the trigger now, it will fail with a compilation error. This is because the dependent class, TimecardManager, has not yet been defined.

Continue on to creating the class. Select File, New, Apex Class to reveal the New Apex Class Wizard. Enter the class name (TimecardManager), leave the other fields (Version and Template) set to their defaults, and click the Finish button.

Listing 4.43 is the TimecardManager class. It performs the work of validating the timecard on behalf of the trigger. First, it builds a Set of resource Ids referenced in the incoming set of timecards. It uses this Set to query the Assignment object. For each timecard, the assignment List is looped over to look for a match on the time period specified in the timecard. If none is found, an error is added to the offending timecard. This error is ultimately reported to the user or program initiating the timecard transaction.

Listing 4.43 TimecardManager Class

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public with sharing class TimecardManager {
  public class TimecardException extends Exception {}
  public static void handleTimecardChange(List<Timecard__c> oldTimecards,
    List<Timecard__c> newTimecards) {
    Set<ID> contactIds = new Set<ID>();
    for (Timecard__c timecard : newTimecards) {
      contactIds.add(timecard.Contact__c);
    }
    List<Assignment__c> assignments = [ select Id, Start_Date__c,
      End_Date__c, Contact__c from Assignment__c
      where Contact__c in :contactIds ];
    if (assignments.size() == 0) {
      throw new TimecardException('No assignments'),
    }
    Boolean hasAssignment;
    for (Timecard__c timecard : newTimecards) {
      hasAssignment = false;
      for (Assignment__c assignment : assignments) {
        if (assignment.Contact__c == timecard.Contact__c &&
          timecard.Week_Ending__c - 6 >= assignment.Start_Date__c &&
          timecard.Week_Ending__c <= assignment.End_Date__c) {
            hasAssignment = true;
            break;
        }
      }
      if (!hasAssignment) {
        timecard.addError('No assignment for contact ' +
          timecard.Contact__c + ', week ending ' +
          timecard.Week_Ending__c);
      }
    }
  }
}