How do I optimize searching 3,000 records for an email that matches one on a lead?

Question

Scenario

A New Lead is inserted, if it matches criteria, the lead ownerid is Updated based on an email field on the lead.

Problem

Write code that takes the email address and queries all Users for one which has an email matching the lead field.

Question

How do I optimize this Operation? I currently am doing it with 3 nested for loop. I would like to do this using a map< email,User> so I can take advantage of the loopups instead of raw iteration. This method is inside a trigger helper class. Newlead is a a map of newleads.

    Public static void updateOwnerIdForPartner() {
    List<lead> leadsToUpdate = new list<lead>();
    List<String> emails = new list<String>();


    for(Lead lead: newLead) {

        if(lead.Sales_Rep_Email__c != null && lead.recordtypeid == '012C0000000M000000' && lead.LeadSource == 'Partner') {
            leadsToUpdate.add(lead);
            emails.add(lead.Sales_Rep_Email__c);
        }
    }
    if(leadsToUpdate.size() > 0) {

        for(List<user> users: [SELECT Id, email FROM user WHERE email IN :emails]) {
            for(User user : Users) {
                for(Lead lead : leadsToUpdate) {
                    if(lead.Sales_Rep_Email__c == user.email) {
                        lead.OwnerId = user.id;
                    }
                }
            }
        }
    }

}

Answer 1

Creating the map is quite simple. It's like any other map, nothing special here.

Map<String, List<Lead>> emailToLeads = new Map<String, List<Lead>>();
for (Lead record : someCollection)
{
    if (!emailToLeads.containsKey(record.Email))
        emailToLeads.put(record.Email, new List<Lead>());
    emailToLeads.get(record.Email).add(record);
}

Note that since multiple records can have the same Email, you use List<Lead> as the map value, rather than a single record. Note also that this field is not unique on User either, so if multiple have the same Email, you will have arbitrarily assign one of them.