How to update custom date field on opportunity when stage field changes from one value to other?

Question

I'm trying to update a custom field on opportunity 'stagechanged__c' field (Date-datatype) when the standard stage changed from Prospecting to Qualification.

how to update date on custom field "stagechanged__c" field when standard stage field changes.

this is my batchjob :

        Global class OpportunityStageChanges implements 
       Database.Batchable<sObject> {


       Global Database.QueryLocator start(Database.BatchableContext BC) {

    String query = 'Select Id,Name,Amount,(Select ID, OldValue, NewValue 
    from OpportunityFieldHistory)from Opportunity';
    System.debug(query);

      return Database.getQueryLocator(query);

     } Global void execute(Database.BatchableContext BC,  

         List<Opportunity> 

       scope) {

         for(Opportunity opp : scope) {


        for(OpportunityFieldHistory opfh : opp.OpportunityFieldHistory) {
          system.debug(opfh.oldValue+'----'+opfh.NewValue );
        if(opfh.oldvalue == 'prospecting' && opfh.newvalue == 'Qualification'){

            //how to update the stagechanged__c custom field
        }

    }
}

}

      Global void finish(Database.BatchableContext BC) {}

     }   

how to update the stagechanged field ?

Thanks In Advance, Sekhar

Answer 1

For this scenario, a Batch class is over-engineering your problem. A trigger would be ideal.

trigger OnOpportunityAfter on Opportunity (before update) {

    for(Id oppId : Trigger.newMap.keySet()) {
        if(Trigger.oldMap.get(oppId).StageName == 'Prospecting' && Trigger.newMap.get(oppId).StageName == 'Qualification' ) {
            Trigger.newMap.get(oppId).stagechanged__c = Date.today();
        }
    }
}

I'm not sure what date you want to use in your custom field.