Is there a way to generate a unique hashcode for an in memory SObject that does not yet have an Id?

Question

When SObjects are used as Map keys they are compared by field values, so for example:

Account a = new Account();
Account b = new Account();
System.debug(a == b); // Prints true

Map<SObject, Boolean> m = new Map<SObject, Boolean>();
m.put(a, true);
m.put(b, false);

System.debug(m.get(a)); // Prints false

What I want instead is for them to be stored as separate keys. I've managed to achieve this by creating a wrapper class and overriding equals() using the exact equality operator (===).

private class SObjectReferenceWrapper
{
    public SObject Record;
        
    public SObjectReferenceWrapper(SObject record)
    {
        this.Record = record;
    }
        
    public Boolean equals(Object obj) 
    {
        if (obj instanceof SObjectReferenceWrapper) 
        {
            SObjectReferenceWrapper o = (SObjectReferenceWrapper)obj;
            return (Record === o.Record);
        }
            
        return false;
    }
}

Usage:

SObjectReferenceWrapper o = new SObjectReferenceWrapper(new Account());
SObjectReferenceWrapper o2 = new SObjectReferenceWrapper(new Account());
System.debug(o == o2); // Prints false

Map<SObjectReferenceWrapper, Boolean> m = new Map<SObjectReferenceWrapper, Boolean>();
m.put(o, true);
m.put(o2, false);

System.debug(m.get(o)); // Prints true

Account a = new Account();
SObjectReferenceWrapper o = new SObjectReferenceWrapper(a);
SObjectReferenceWrapper o2 = new SObjectReferenceWrapper(a);
System.debug(o == o2); // Prints true

Map<SObjectReferenceWrapper, Boolean> m = new Map<SObjectReferenceWrapper, Boolean>();
m.put(o, true);
m.put(o2, false);

System.debug(m.get(o)); // Prints false

Unfortunately, relying on equals() alone causes put() calls to take an incredibly long time once the map has 10-15 keys in it, so I need to implement hashCode() to resolve this. This is where I've come unstuck.

When all of the field values are the same the build in hashCode() method returns the same value, so that's no use.

I did also consider using the memory addresses of the objects which are show in in debug logs under VARIABLE_ASSIGNMENT, however it doesn't look like these are exposed via. Apex.

Have I come to a dead end where the limitations of the platform make this impossible (I hate that word), or am I missing something really obvious?

tl;dr

I need to create a Map using in memory SObjects as keys. Each in memory SObject should be treated as a unique value if it occupies a different location in memory, even if they have the same field values. Is this possible?

Answer 1

public class Wrapper {
    Sobject record;

    public Integer hashCode() {
        return System.hashCode(record);
    }

    public Boolean equals(Object o) {
        return record === ((Wrapper)o).record;
    }

    Wrapper(SObject record) {
        this.record = record;
    }
}

This works by using ===, which is a memory compare function. Test code ensues:

@isTest
public class sfse46415 {
    public class Wrapper {
        Sobject record;

        public Integer hashCode() {
            return System.hashCode(record);
        }

        public Boolean equals(Object o) {
            return record === ((Wrapper)o).record;
        }

        Wrapper(SObject record) {
            this.record = record;
        }
    }


    public static testmethod void test() {
        Contact a1 = new Contact(LastName='Test'),
                b1 = new Contact(LastName='Test'),
                c1 = new Contact(LastName='Test 2');
        Wrapper a2 = new Wrapper(a1),
                b2 = new Wrapper(b1),
                c2 = new Wrapper(c1),
                a3 = new Wrapper(a1),
                b3 = new Wrapper(b1),
                c3 = new Wrapper(c1);
        Set<Wrapper> items = new Set<Wrapper>();
        items.add(a2);
        System.assertEquals(true , items.contains(a2));
        System.assertEquals(false, items.contains(b2));
        System.assertEquals(false, items.contains(c2));
        System.assertEquals(true , items.contains(a3));
        System.assertEquals(false, items.contains(b3));
        System.assertEquals(false, items.contains(c3));
        items.add(b2);
        System.assertEquals(2, items.size());
        System.assertEquals(true , items.contains(a2));
        System.assertEquals(true , items.contains(b2));
        System.assertEquals(false, items.contains(c2));
        System.assertEquals(true , items.contains(a3));
        System.assertEquals(true , items.contains(b3));
        System.assertEquals(false, items.contains(c3));
    }
}

Answer 2

If I understand correctly...

You can set a static variable at 0 somewhere.

public class MyHashes
{
  private static Integer myHash = 0;

  //This lets nowhere outside control it and so you will get a new one each time
  public static Integer getNextHash()
  {
    ++myHash;
    return myHash;
  }
}

Modify your wrapper class.

private class SObjectReferenceWrapper
{
  public SObject Record;
  public Integer hash;

  public SObjectReferenceWrapper(SObject record)
  {
    this.Record = record;
    hash = MyHashes.getNextHash();
  }

  public Boolean equals(Object obj) 
  {
    if (obj instanceof SObjectReferenceWrapper) 
    {
        SObjectReferenceWrapper o = (SObjectReferenceWrapper)obj;
        return (hash == o.hash);
    }

    return false;
  }
}

Answer 3

Summer 14 introduced a new System.hashCode(Object) static method that may do what you're looking for. I believe if your object implements hashCode() it invokes and returns the value provided, but if not it uses some internal definition that appears to be very quick.

Answer 4

I think the problem that you are having is that the ID is uninitialized (could be wrong, maybe its 0?) and Map uses the SObject's ID as the key.

It is not until they are inserted into the database that they are assigned UNIQUE Id's, even if they have the same information.

I think you need to insert your new accounts (or records in general) into the database with insert <record var>, the SObject reference will update automatically with the assigned unique ID, and map with thus be able to distinguish them.