Join fetch fails on fetching 3rd level relationship

João Menighin :

I have three entities: Person, Country and CountryTranslation. Person is related to one Country and Country have many CountryTranslations.

I want my query to fetch both Country and CountryTranslations when it fetches a Person in order to avoid multiple queries.

To bring the Country along with Person I do:

List<Person> persons = (List<Person>) entityManager
                .createQuery("SELECT person from Person person " +
                             "left join fetch person.country")
                .getResultList()

This works fine, I see on hibernate it is fetching nicely and no extra queries are executed to bring Country, but to bring CountryTranslations it still execute extra queries. Then I tried:

List<Person> persons = (List<Person>) entityManager
                .createQuery("SELECT person from Person person " +
                             "left join fetch person.country " +
                             "left join fetch person.country.translations")
                .getResultList()

And I get the error:

org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list 

What is the right way to do this fetching?

Thanks in advance

Henrique Mentz :

You correct this giving an alias for each relationship.

SELECT person 
FROM  person person 
LEFT JOIN FETCH person.country country 
LEFT JOIN FETCH country.translations

It's a framework's "limitation": When you use linked fetchs you should to give an alias for each relationship!

This behavior can also be explained because will be difficult to understand what these linked fetches really mean: Does the framework will fetch each relationship or only the last one? It's more simple to just tell to the framework what fetch relationship you want.