model: Model class
    fields: List of 2-tuples of the form (field, value) in order of descending priority

def resolve_model(model, fields):
    """
    model: Model class
    fields: List of 2-tuples of the form (field, value) in order of descending priority
    """
    for (f, v) in fields:
        if v is not None:
            try:
                kwargs = {f: v}
                obj = model.objects.get(**kwargs)
                return obj
            except model.DoesNotExist:
                pass
            except model.MultipleObjectsReturned:
                pass
    raise model.DoesNotExist()