Looking around the net it appears that the best place to hook into the Lead Conversion process is in a Trigger's After Update event.

I have a situation where I have a related object on a lead and upon conversion, for those that create a new Contact I want to do one thing, but if it's a merge with an existing contact I want to do another.

My problem is, I can't figure out how to know whether the merge was to an existing contact or new contact.

I would think that ConvertedContactId would give me a value for both new and merge?

    if (lead.IsConverted && !trigger.oldmap.get(lead.id).IsConverted) {
        // Handling conversion

        // Step 1 - get all existing Status Trackers for lead, that are not Existing Contacts
        //   and migrate to new Contact id

        // Step 2 - get all existing Status Trackers for lead -- that are for 
        //   existing Contacts and delete them
    }

Attribution to: codethrift

Possible Suggestion/Solution #1

This post provided the order of execution of triggers for Lead Conversion.

A couple of ways :

• The Contact CreatedDate would be in the past, you could compare with a safety margin in mind, so you know that the Contact was created in advance of the Lead being converted.

• The Contact triggers fire before the Lead triggers, therefore in a ContactBefore trigger you could add the ContactIds of records where the trigger.IsInsert to a static Map/ Set. Being static this would also be available in the lead after, where you can check if the ConvertedContactId was in this Set / Map of newly Created Contacts and then vary your behaviour based on that.

I can't for the life of me think of a simpler solution. (part of me wonders if the ConvertedContactId is available sooner, say in a LeadBefore trigger when it is converted into an existing contact)

Attribution to: techtrekker

Possible Suggestion/Solution #2

If you can, you could add a new checkbox to the Lead, Was Converted, and mark it true. This could serve as a flag to check in your trigger.

Attribution to: Mike Chale

Possible Suggestion/Solution #3

Thanks for both of your ideas. I realized before your answers that whenever we do a Lead conversion due to having a duplicate Contact for a Lead, we choose the Lead Status = "-Merge Contact".

Like Mike suggested, I used that value to trap for those types. Here's the code if someone needs it in the future:

    if (lead.IsConverted && !trigger.oldmap.get(lead.id).IsConverted) {

        // process all merges that had to do with Contacts
        if (trigger.newmap.get(lead.id).ConvertedContactId <> null) {

            if(trigger.newmap.get(lead.id).Status == '-Merge Contact') {
                // Existing Contact
                // Delete all existing Status Trackers for lead                 
                leadIdsToDeleteStatusTracker.add(lead.id);  
            }
            else {
                // New Contact
                // Get all existing Status Trackers for lead and migrate to new Contact id  
                leadIdContactIdToUpdateStatusTracker.put(
                        lead.id,
                        trigger.newmap.get(lead.id).ConvertedContactId
                    );                                                      
            }               
        }

    }

Attribution to: codethrift
This content is remixed from stackoverflow or stackexchange. Please visit https://salesforce.stackexchange.com/questions/4664