Cannot create typedquery for query with more than one return using requested result type

When you receive the error message “cannot create typedquery for query with more than one return using requested result type”, it means that you are trying to use the TypedQuery interface in JPA (Java Persistence API) with a query that returns multiple entities or values but you have specified a single result type.

TypedQuery is used to create a query that has a specific result type specified by the generic type parameter. When you try to create a TypedQuery with a query that returns more than one result, you need to specify a result type that can accommodate those multiple values.

Let’s look at an example to understand this better:

    EntityManager em = getEntityManager();
    TypedQuery<User> query = em.createQuery("SELECT u FROM User u", User.class);
    User user = query.getSingleResult();
  

In this example, we are trying to retrieve a single User entity from the database using a TypedQuery. However, if there are multiple User entities in the result set, we will receive the “cannot create typedquery for query with more than one return using requested result type” error. This is because we are specifying a single User class as the result type, which cannot accommodate multiple entities.

To fix this error, you have a few options:

• If you expect multiple entities in the result set, you can change the query to return a List of entities instead of a single result:

          List<User> users = query.getResultList();
        

  This way, you retrieve all the User entities and store them in a List.

• If you only expect a single result but want to handle the possibility of multiple results, you can use the setMaxResults() method to limit the results to one:

          TypedQuery<User> query = em.createQuery("SELECT u FROM User u", User.class);
          query.setMaxResults(1);
          User user = query.getSingleResult();
        

  This way, even if there are multiple User entities in the result set, you will only retrieve the first one.

• If you want to retrieve multiple values that are not entities, you can change the result type to Object[] (array of Objects) and modify your query accordingly:

          TypedQuery<Object[]> query = em.createQuery("SELECT u.id, u.name FROM User u", Object[].class);
          List<Object[]> results = query.getResultList();
          for (Object[] result : results) {
            Long id = (Long) result[0];
            String name = (String) result[1];
            // Process the values accordingly
          }
        

  In this example, we are selecting only the id and name fields from the User entity and retrieving them as an array of Objects. We then iterate over the result set and cast the array elements to their respective types.