How select column at rune time using JPA (JPQL or Criteria API)?

Question

I've searched here on SO and the web but couldn't find an answer to this problem. How do I write the following MySQL query using JPQL or JPA's Criteria API?

public String getLanguage(String language) { 
    String query = "SELECT i18n." + language + " AS translated FROM i18n";
}

I realise this specific query is meaningless, but the problem for me is to choose column dynamically. Ie select i18n.language where 'language' is chosen at run time.

I could imagine it to look something like:

public List getLanguage(String language) {
    return entityManager.createQuery(
        "SELECT l.:language FROM I18n i"
    ).getResultList();
}

but this doesn't compile. Thanks

Answer 1

You can't do it with parameter, since the parameter can't be used to replace column name, but you can do it in a way similar to what you do in plain SQL

public List getLanguage(String language) {
    return entityManager.createQuery("SELECT i." + language + " as translated FROM I18n i").getResultList();
}

EDIT

One way to do it with parameter, but it's not really dynamical solution, you would have to hard code all the options

SELECT CASE WHEN :language = 'EN' THEN i.en WHEN :language = 'MK' THEN i.mk END as translated FROM I18n i"