methode JEE implementation - jpa

Question

I implemented a method that allows me to generate a test ( entire of question ) automatically but the problem is :
the method will obviously take the number of random questions but also the category of questions generated (I have a entié category and therefore a table too) I don't know where i will put the category in query.
and secondly RANDOM() is not taked by JPQL what can i do ?
schema of the DataBase
public List<Question> prepareRandomTest(int number_of_questions, Categorie categorie){
String jpql = "SELECT q FROM Question q ORDER BY RANDOM() LIMIT "+number_of_questions ;
Query query = entityManager.createQuery(jpql);
return query.getResultList();
}

Answer 1

You are trying to use Java Persistence Query Language here, Hence your solution is not taking RANDOM into account. Use Native query and build Query from native sql string, Native query is just a plain sql statement without Entity object reference (like Question). This way a normal sql keywords like RANDOM etc are easily read.
Native Query Tutorial
Instead of Using
String jpql = "SELECT q FROM Question q ORDER BY RANDOM() LIMIT "+number_of_questions ;
use:
"SELECT * FROM question where category="+category+" ORDER BY RANDOM() LIMIT "+number_of_questions;
Additional Advice:
Get the category string from an "Enum" in your code to match the string value in the database category column.