Reasons for choice of relationship field type (master-detail or lookup)?

[sfdevnick]

Here's what I've gathered so far:

1. Use master-detail when you want the detail object to delete along with the master object.
2. Offline edition only supports master-detail, not lookup. (I think the Mobile Edition upports both though).
3. Email templates only support master-detail, but not lookup (can anyone confirm this is still true in Summer 08?).
4. Objects can only have one Master-Detail relationship field. (can anyone confirm this is still true in Summer 08?)
5. Roll up summary field on parent only works on child objects where relationship is master-detail

Anyone know any more? I'm especially interested in understanding how decision impacts custom reports, custom report types and views - and any other gotchas/limitations on either side.

[Mehmet_Ergun]

The biggest difference is that cascading deletes are not supported when using lookups.. And you can't have multiple master detail relationships... I've found that the biggest use of master detail relationships for me is the cascading deletes... You can get around the lack of multiple master-details but you have to write code to delete children when the kids are based on lookup relationships.  Since this is something that's often used, I have written a generic class and use a configuration table that mimmics the master detail cascade deletes.  It works, but, you have to watch out for SOQL limits if you have a very complicated or large object structure where you want to mimmic the master detail cascading deletes.

 First create a admin configurable table called sa_CascadeDeletes__c with text fields parent_object__c, child_object__c, Lookup_Field_Name__c - populate these records manually with your object relationships

 Call the class from any trigger that you want to cascade (from kids, grankids, etc.) with a simple oneliner - pass in the name of the triggering object and the keyset of records being deleted.

trigger DeleteKids on Account_Kids__c (before delete) {

If (Trigger.IsDelete) {


    sa_CascadeDeleter.DeleteChildren('Account_Kids__c', trigger.oldmap.keyset());

}


}

public class sa_CascadeDeleter {

  public static void DeleteChildren(String strPO, Set<Id> setDeletes) {

//PREREQ:  sa_CascadeDeletes object with fields parent_object__c, child_object__c, Lookup_Field_Name__c
//USAGE:
// 1) Called from Delete Trigger, Takes the parent object name as string and a set of record ids being deleted as input parameters
// 2) Looks up the child-object(s)-to-delete in the sa_cascadedeletes table
// 3) Deletes all indicated children records, if any, returns nothing

   
    // Create a list of child objects that are configured in sa_CascadeDeletes to cascade delete from parent object
    String strQCD = 'select id, parent_object__c, child_object__c, Lookup_Field_Name__c from sa_CascadeDeletes__c where parent_object__c = \'' + strPO + '\'';
    List<sa_CascadeDeletes__c> cds = Database.Query(strQCD);

            system.debug(setDeletes.size());
            integer i = setDeletes.size();

            String strIDs = '\'';
            For ( id myID  :setDeletes ) {
            system.debug (myID);
            strIDs = strIDs + myID;
            If (i != 1) {
            strIDs = strIDs + '\',\''; }
            i--;
            }
            strIDs = strIDs + '\'';

   
        // For each child object set to cascade delete, repeat this loop  
        For (sa_CascadeDeletes__c cd : cds) {
    
            system.debug(cd.child_object__c);
            system.debug(cd.Lookup_Field_Name__c);         

             String strQCO = 'select id from ' + cd.child_object__c + ' where ' + cd.Lookup_Field_Name__c + ' in (' + strIDs + ')';

     
            system.debug(strQCO);
            List<sObject> lDeleteKids = Database.query(strQCO);
            Delete lDeleteKids;
        
        }    



}


}