How to check if SObject has certain field?

Question

I hope you'll help me to solve my problem :)

I've written a class that check if a Sobject has a field of a certain name

public static boolean hasSObjectField(String fieldName, SObject so){
    return so.getSobjectType().getDescribe().fields.getMap().keySet().contains(fieldName);
}

It works very fine, but there is one fault: it does not check system fields such as, for example, OwnerId.

Can you tell me what I've done wrong?

Regards!

Answer 1

All the keys in the map are in lower case for some reason. I get a positive result for ownerid but not for OwnerId. I checked for our account object and all the keys in the map are lowercase.

This i think should fix it:

public static boolean hasSObjectField(String fieldName, SObject so){
            return so.getSobjectType().getDescribe().fields.getMap().keySet().contains(fieldName.toLowerCase());
}

Answer 2

If you use dynamic SOQL and just wanna check results without try/catch or going thru metadata describe, you can use SObject.isSet() method.

Answer 3

Usually I'll just go ahead and write the code, assuming the field does exist, and catch the exception if it doesn't. e.g.

if(Trigger.isBefore && (Trigger.isInsert || Trigger.isUpdate))) {
    try {
        for(SObject o : Trigger.new) {
            Id ownerId = null;
            String s = String.valueOf(o.get('OwnerId'));
            if(s != null && s.startsWith('005')) {
                ownerId = (Id)s;
            }
            if(ownerId != (Id)o.get('Owner__c') ) {
                o.put('Owner__c',ownerId);
            }
        }
    }
    // if the field does not exist, an exception will be thrown
    catch(SObjectException ex) {
        System.debug(ex);
    } 
}

In most cases this is much faster, since presumably you are using fields that should exist and this is just to handle the niche scenarios.

If you really do need to check the field say because you are building up a field map for a custom query, then the previous answer works fine.