Hello,

I am currently trying to build a quite big soql query.

This query should result in a list of custom objects which are filtered by values entered by a user via a form i built.

There are two lookup fields in this form where the user can select the correlating account and one other custom object.

I am getting the IDs from the fields as ID type so that there is no problem with 15 vs 18-character IDs.

The problem is now that the form should be exclusively searching for values in those fields that were entered by the user.

Right now, if i don't select a value in both fields, the query results in an error.

Here is my method executing the query:

public PT_System__c ptsystem;
public Rental__c rental;
public String accString;
public Id searchAccount;
public String sysString;
public Id searchSystem;

public List<Rental__c> getFilteredAnlagen(){
           if(rental.PT_System__c != null){
               sysString = rental.PT_System__c;
               searchSystem = (Id)sysString;
               }else{searchSystem = '%';}
           if(rental.account__c != null){
               accString = rental.account__c;
               searchAccount = (Id)accString;
           }else{searchAccount = '%';}
           if(String.valueOf(rental.Start__c) != '' || rental.Start__c != null){
               searchStart = String.valueOf(rental.Start__c);
           }else{searchStart = '%'+String.valueOf(rental.Start__c);}
                  return [select Id, Name 
                          FROM Rental__c 
                          WHERE PT_System__r.RecordType.Name = 'Rental System' 
                          AND PT_System__r.Id = :searchSystem 
                          AND Account__c = :searchAccount
                          order by name];
       }

 As you can see, i used the '%' as a wildcard like i would use it for a string, which obviously is not working.

How can i check, if the related fields are selected and only search for those entries in the query when they are.

Or is there any other wildcard character that can be used for an ID?

The problem is, that there are a couple more fields in the form that should be able to be searched in without having to select an account or System.

I would appreciate any help with this, as i am totally stuck with it right now.