Custom History Tracking on Opportunity with trigger

Question

Trigger:

 

Custom Opportunity History Tracking

• Create Custom Object : OpportunityHistory

• Fields : Field Name(Text), Old Value(Text) and New Value(Text)

Trigger Logic: 

 

• When new opportunity is inserted in the system, It creates history record with Field Name = ‘Record Created’.

• When Record is updated, it first identifies which all fields got updated  and then it creates 'OpportunityHistory’ record one for each updated field with Field Name, Old Value and New Value information

I have currently written code just to check the 'NextStep' field. I am not able to proceed further, Unable to fetch and check all fields in Opportunity. Edited the code, just updated trigger is writter in the code. Code:

trigger OpportunityHistory on Opportunity (after update) {
    for(Opportunity opp : Trigger.new) {
        System.debug('NEW MAP' +opp );
        Opportunity oppOld = Trigger.oldMap.get(opp.Id);
        System.debug('OLD MAP' +oppOld );
        OpportunityHistory__c oppHist = new OpportunityHistory__c();
        if(oppOld.NextStep != opp.NextStep) {
            oppHist.Opportunity__c = opp.Id;
            oppHist.Field_Name__c  = 'Record Created 2.0';
                oppHist.Old_Value__c = oppOld.NextStep;
                System.debug('Old Next Step Value: ' +oppHist.Old_Value__c );
                oppHist.New_Value__c  = opp.NextStep;
                System.debug('New Next Step Value: ' +oppHist.New_Value__c );
            insert oppHist;
        }
    }
}

Answer 1

If you want to iterate all fields, you can get them from the describe map:

DescribeSObjectResult describe = SObjectType.Opportunity;
List<SObjectField> opportunityFields = describe.fields.getMap().values();

However, it may be better to just iterate populated fields:

for (Opportunity record : trigger.new)
{
    Map<String, Object> populatedFields = record.getPopulatedFieldsAsMap();
    // further processing
}

You should move your logic into separate classes, as it will simplify building out further logic. Your basic class structure would look something like:

public with sharing class OpportunityHistoryService
{
    public static void trackHistory
        (List<Opportunity> newRecords, Map<Id, Opportunity> oldMap)
    {
        List<OpportunityHistory__c> histories = new List<OpportunityHistory__c>();
        for (Opportunity record : newRecords)
        {
            histories.addAll(getHistories(record, oldMap.get(record.Id));
        }
        try
        {
            // don't neglect error handling
            // naked DML in a trigger should be avoided at all cost
            insert histories;
        }
        catch (DmlException dmx)
        {
            // what should you do if the records fail?
            // DO NOT leave this code block empty (comments/debug don't count)
            // empty catch block is even worse than naked DML
        }
    }
    public static List<OpportunityHistory__c> getHistories
        (Opportunity newRecord, Opportunity oldRecord)
    {
        // implementation
    }
}