JPA: How to get entity based on field value other than ID?

In JPA (Hibernate), when we automatically generate the ID field, it is assumed that the user has no knowledge about this key. So, when obtaining the entity, user would query based on some field other than ID. How do we obtain the entity in that case (since em.find() cannot be used).

I understand we can use a query and filter the results later. But, is there a more direct way (because this is a very common problem as I understand).