Map records without Id to their related records

I recently encountered a task involving a multi-layered data structure. To outline the requirements concisely:

• Trigger: The process is initiated by an Insert trigger, which supplies a list of newly added Leads.
• Account Lookup: Each Lead within this list contains a reference to a corresponding Account.
• Contact Mapping: The objective is to retrieve the primary Contact associated with each Account and establish a direct link between that Contact and its respective Lead.

Assumption

• Leads are new and therefore no Id exist.
• To simplify, we ignore every null value in lookups.
• Also we will ignore all the conditions.

Solution

We know that we need to avoid Query in a loop, therefore, the crucial step involves constructing a Map that correlates Leads with their corresponding orders.

Integer counter = 0;
Map<Integer, Lead> newLeadMap = new Map<Integer, Lead>();
for (Lead l : newLeads) {
     newLeadMap.put(counter++, l);
}

Secondly, we will get all the Account Ids associated with Leads.

Set<Id> accountIdSet = new Set<Id>();
for (Integer key : leadMap.keySet()) {
     accountIdSet.add(leadMap.get(key).account__c);
}

And we query all Contacts that has a lookup to those Accounts.

List<Contact> contacts = [SELECT Id, AccountId
     FROM Contact
     WHERE AccountId IN :AccountIds];

Next, let’s get a map of Accounts with their corresponding Contacts.

Map<Id, List<Contact>> accountIdToContactListMap = new Map<Id, List<Contact>>();
for (Contact con : contacts) {
     List<Contact> contactList = accountIdToContactListMap.get(con.AccountId);
     if (contactList != null) {
          contactList.add(con);
          accountIdToContactListMap.put(con.AccountId, contactList);
     } else {
          accountIdToContactListMap.put(con.AccountId, new List<Contact>{ con });
     }
}

Now it’s easy to find the primary Contact.

Map<Id, Contact> accountIdToContactMap = new Map<Id, Contact>();
for (Id acctId : accountIdToContactListMap.keySet()) {
     Boolean primaryContactFound = false;
     for (Contact con : accountIdToContactListMap.get(acctId)) {
          if (con.Is_Primary__c == true) {
               accountIdToContactMap.put(con.AccountId, con);
               break;
          }
     }
}

Cool! Last thing to do is to Map primary Contacts with the Leads.

Map<Integer, Contact> result = new Map<Integer,Contact>();
for (Integer key : leadMap.keySet()) {
     Contact con = accountIdToContactMap.get(leadMap.get(key).account__c);

     result.put(key, con);
}

Remember that every Key value was a replacement for the Lead Id.