Associate Contact with no Account Id to Bucket Account

Test Script

@isTest
private class ContactAssociateAccount_TEST {

@isTest
private static void testblankaccountid() { 
//First test when no Account exists

Contact testc = new Contact (LastName = 'Test Contact 1');
insert testc;

List<Contact> checkresult = [SELECT Id, LastName, AccountId, Account.Name FROM Contact WHERE Id = :testc.Id];
system.assertequals(1, checkresult.size());
system.assertequals('Citizen', checkresult[0].Account.Name);

//Now check a second contact gets added to same account
 
Contact testc2 = new Contact (LastName = 'Test Contact 2');
insert testc2;

checkresult = [SELECT Id, LastName, AccountId, Account.Name FROM Contact WHERE Id = :testc2.Id];
system.assertequals(1, checkresult.size());
system.assertequals('Citizen', checkresult[0].Account.Name);

List<Account> checkaccountresults = [SELECT Id, Name, (SELECT Id FROM Contacts) FROM Account WHERE Name = 'Citizen'];
system.assertequals(1, checkaccountresults.size());
system.assertequals(2, checkaccountresults[0].contacts.size());

//Now create new account and check new contact at existing account works
Account testa = new Account (Name = 'Test A');
insert testa;

Contact testc3 = new Contact (LastName = 'Test Contact 2', AccountId = testa.Id);
insert testc3;

checkresult = [SELECT Id, LastName, AccountId, Account.Name FROM Contact WHERE Id = :testc3.Id];
system.assertequals(1, checkresult.size());
system.assertequals('Test A', checkresult[0].Account.Name);
 
}


@isTest
private static void testblankaccountidbulk() { 
//Test in bulk with 50% at no account, 50% at existing

//Create new account and check new contact at existing account works
Account testa = new Account (Name = 'Test A');
insert testa;

List<Contact> testcons = new List<Contact> ();
for (Integer i=0;i <100;i++) {
testcons.add(new Contact(LastName = 'TestC' + String.valueof(i)) );
}

for (Integer i=100;i <200;i++) {
testcons.add(new Contact(LastName = 'TestC' + String.valueof(i), AccountId = testa.Id));
}

insert testcons;

List<Account> checkaccountresults = [SELECT Id, Name, (SELECT Id FROM Contacts) FROM Account WHERE Name = 'Citizen'];
system.assertequals(1, checkaccountresults.size());
system.assertequals(100, checkaccountresults[0].contacts.size());

checkaccountresults = [SELECT Id, Name, (SELECT Id FROM Contacts) FROM Account WHERE Id  = :testa.Id];
system.assertequals(1, checkaccountresults.size());
system.assertequals(100, checkaccountresults[0].contacts.size());
 
}



}

Trigger

rigger ContactAssociateAccount on Contact (before insert) {
Boolean noAccount = FALSE;

for (Contact c : Trigger.new) {
    if (c.AccountId == null) {
        noAccount = true;
        break;
    }
}

if (noAccount) {
    Account[] citizen = [select Id from Account where name = 'Citizen' limit 2];

        if (citizen.size() == 0 ) {
        //create citizen account
            citizen = new Account[1];
            citizen [0] = new Account(name='Citizen');
        insert citizen ;
        }
    
    for(Contact c : Trigger.new) {
    //set contact as a citizen
        if (c.AccountId == null) {
            c.AccountId = citizen[0].id;
        }
    }
    
}

}

This is a pretty crude trigger but will get the job done. You could move the name of the bucket account into a custom setting to make it more flexible. You would also normally move the trigger code into a separate handler, but assuming this is temporary to get you over the initial hill, you can leave as is...

You should also think about Data Skew sooner rather than later - anything other 10k contacts at a single account can cause issues...