Is it possible to cause an exception on a SOQL select statement?

Question

I'm working on writing tests for someone else's code and they have an try/catch around a SELECT statement. Is it possible to ever get an exception in something like the below code block as long as it is being returned to a list? I'm trying to find out if I need to cover the exception block or if I can just remove it.

I know it can happen if you are returning the results to a single object and it doesn't have any results to return, but I don't think it is possible if you return to a list. I'm trying to find if there is an official answer that I can point to if I'm questioned on why I'm removing the try/catch.

public static void processOpportunity(Id opportunityId) {
        List<Opportunity> opportunities;
        try {
            opportunities = [SELECT Id, Name FROM Opportunity WHERE Id = :opportunityId];
        }
        catch (Exception ex) {
            System.debug('Exception: ' + ex.getMessage());
            // log exception
        }

        // do stuff with opportunity
    }

Answer 1

No, that construct cannot throw any catchable exception. It can throw LimitException, but that's irrelevant because you cannot catch it.

More generally, handlers that catch the generic Exception and "handle" it via System.debug() are a terrible pattern that produces unexpected, integrity-breaking behavior in code and makes debugging a nightmare. There are few to no situations where this construct should be used.

The answer to the more general question in your title, though (as it sounds like you're already aware) is yes. There are multiple reasons a SOQL statement other than this one can cause an exception to be thrown, including assigning a query result returning something other than a single result to an sObject variable, using the FOR UPDATE clause and failing to get a lock, and using the WITH SECURITY_ENFORCED clause.

Answer 2

You could get a QueryException either by row locks (i.e. another process has queried the record and is still running), or by passing in an invalid Id. For example:

YourClass.processOpportunity('006000000000000AAA');

This will fail to query the record, since that's not actually a record you can query.

In practice, though, it doesn't usually make sense to use try-catch blocks unless you're also using a FOR UPDATE clause to lock the record (which I would advise anyways, if you intend to update a record).

Answer 3

Technically a query can throw a catchable exception. If it attempts and fails to row lock, you will get a QueryException.

try
{
    opportunities = [SELECT ... FROM Opportunity WHERE ... FOR UPDATE];
}
catch (QueryException e)
{
    // failed to lock row
}