Hello again!
I just developed an Apex class for performing replace/merge operations on any kind of object, and yes any kind of relations as well! , so it doesn’t matter if you have master-detail relationships that can’t be modified, objects tied in a master-detail relationship will be cloned, deleted and inserted with the new values to simulate a merge operation!
To use the Merge class just create an ObjectMerge instance, passing as an argument of the constructor your current record:
ObjectMerge oMerge = new ObjectMerge(SourceObject);
And to peform the merge operation just use the replaceRecord method and thats it!, you can specify if you want to delete the source record after the merge operation is done.
oMerge.replaceRecord(MergeToThisObjectID,DeleteSourceObject);
You can limit the number of records that will be processed in the merge operation for Master-Detail relations to avoid hitting governor limits. The ObjectMerge class will let you know if there are any objects left, and if this is the case just continue performing the merge operation.
Force.com provides a merge DML operation but it’s only available for some of their standard objects, this class can help you get around that. There are still some limitations with this class due to governor limits in the number of describe calls but unless you have a large amount of objects related to the replaced/merged record it should work pretty well.
For now, the Object Merge class only merges/replaces custom objects related to your record, but this can be changed in the class , however keep in mind that no more than 10 relations can be processed due to describe calls limitations so be careful when removing the custom objects limitation because there can be many Non-Custom objects related to your record.
I’ll leave a link in this post to the files but for now here’s an example of how to use the ObjectMerge class in a VisualForce controller that merges contacts, if you have custom objects tied a contact A and want to merge contact A to Contact B you will see how the ObjectMerge class changes all of the objects from contact A to contact B then deletes contact A. Remember, you can try it with any custom object 
Enjoy!
Download the files from here –> ObjectMerge
public class MergeController{
//This is just an Aux Object to get a Lookup Field in the VisualForce Page
public Contact MergeAux{get;set;}
//Declare an instance of the Object Merge Class
private ObjectMerge oMerge;
//Save the current contact in the controller (optional)
private final Contact currentContact;
public MergeController(ApexPages.StandardController controller){
//Initialize all of our objects
currentContact = (Contact)controller.getRecord();
MergeAux =new Contact();
oMerge = new ObjectMerge(currentContact);
}
//Merge Action
public PageReference doMerge(){
try{
//Run the merge operation!, you can specify a second argument to delete the record after merge or not
oMerge.replaceRecord(MergeAux.ReportsToId,false);
//Do corresponding actions if merge operation was successful
if(oMerge.bAppliedReplace){
PageReference ref = new PageReference('/'+MergeAux.ReportsToId);
ref.setRedirect(true);
return ref;
}else{
return null;
}catch(Exception e){
ApexPages.addMessages(e);
return null;
}
}
}
//And the Visual Force page will look something like this:
<apex:page standardController="Contact" extensions="MergeController">
<apex:form >
<apex:pageBlock >
<apex:pageMessages id="messages">
</apex:pageMessages>
<apex:pageBlockButtons >
<apex:commandButton value="Merge" action="{!doMerge}" rerender="messages"/>
</apex:pageBlockButtons>
<apex:pageBlockSection columns="1">
<apex:outputField value="{!Contact.Name}"/>
<apex:inputField value="{!MergeAux.ReportsToId}"/>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>
(NOTE: There’s a bug with the code viewer plug-in, please ignore the second viewer)
