Check lookup field is null in apex

Question

What is the best approach to check if a lookup field is null in apex?

rec.lookupField__c == null;         // OR
rec.lookupField__c == '';           // OR 
String.isBlank(rec.lookupField__c ) // ?

I apologize if this is the same as How to check in Apex if a Text field is blank. I posted this anyway because I need confirmation on the approach specifically for a lookup field. The linked question talks only about text field. I am not sure if it is completely safe to consider a lookup field as a text field in this scenario.

Answer 1

Just compare against null directly (your first example).

Your second approach will always yield false.

Your third approach is about twice as slow as the first.

Answer 2

This is also a safer method -

    static public String validateId(String Idparam) {
            String id = String.escapeSingleQuotes(Idparam);
            if((id.length() == 15 || id.length() == 18) && Pattern.matches('^[a-zA-Z0-9]*$', id))
              {
                return id;
              }
            return null;
    }

Answer 3

As everyone suggest you should go with lookupField__c == null. This will always give you correct result.

Or if you want to check if this is correct id and your value store in string then use

If(IdParam InstanceOf Id)
    return true;

Or a better approach what @Keith c Suggest store them in id field and then SF will handle them and will throw exception if you assign wrong value.

Id idparam;