SOQL to dynamically identify all its child object

Question

Payment1 and Payment2 has a lookup relationship with Case. Now I need to write a SOQL to get call its child object dynamically. Case could have record for Payment1 or Payment-2 or both Payment-1 and Payment-2.

List<Case> caseList = [Select Id,OwnerId, (select Id, OwnerId, CreatedById from Payment__r), 
                                        (select Id,OwnerId,CreatedById from Payment_2__r) 
                                         FROM Case 
                                         WHERE Id IN :newCasesMap.keySet()];

How to identify the Payment-1 only present or Payment-2 only present or both Payment1 and Payment-2 present ?

Answer 1

Keeping the query you already have, the code could look like this:

for (Case c : caseList) {
    Boolean p1 = c.Payment__r.size() > 0;
    Boolean p2 = c.Payment_2__r.size() > 0;
    if (p1 && p2) {
        // Add code for both present
    } else if (p1) {
        // Add code for p1 only present
    } else if (p2) {
        // Add code for p2 only present
    } else {
        // Add code for neither present
    }
}

Note that the relationship name from parent to child normally defaults to a plural; if that is the case here the names would be Payments__r and Payment_2s__r.

If you don't need the payment records and just want to count them, you could use an aggregate query instead.