Question

I want to update a record if the record exists or insert a new one if it doesn’t.

What would be the best approach?

Do a Select Count() and if comes back zero then insert, if one then query the record, modify and update,
or should I just try to query the record and catch any system.queryexception?

This is all done in Apex, not from REST or the JS API.

Answer 1

Adding to what’s already been said here, you want to use FOR UPDATE in these cases to avoid what superfell is referring to. So,

Account theAccount;
Account[] accounts = [SELECT Id FROM Account WHERE Name = 'TEST' LIMIT 1 FOR UPDATE];
if(accounts.size() == 1)
   theAccount = accounts[0];
else
   theAccount = new Account();

// Make modifications to theAccount, which is either:
// 1. A record-locked account that was selected OR
// 2. A new account that was just created with new Account()

upsert theAccount;