Question

我是hibernate的新手，并且正在努力为标准查询添加单个投影。我收到以下代码的错误：＆＃34; java.lang.Integer无法转换为[Ljava.lang.Object，在第29行。我知道这很简单，但我无法弄清楚我是什么在这里做错了！

代码如下：

package com.simpleprogrammer;

import org.hibernate.Criteria;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.criterion.Projection;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Restrictions;

import java.util.Date;
import java.util.List;
import java.util.Objects;

public class Program {
public static void main(String[] args) {
    System.out.println(org.hibernate.Version.getVersionString());
    System.out.println("Creating session!");

    PopulateSampleData();
    Session session = HibernateUtilities.getSessionFactory().openSession();
    session.beginTransaction();
    Criteria criteria = session.createCriteria(User.class);
    criteria.add(Restrictions.eq("name", "Joe")).setProjection(Projections.property("id"));
    List<Object[]> results = criteria.list();

    for(Object[] result : results) {
        for (Object o : result)
            System.out.println("Name is " + o.toString());
    }
    session.close();
    HibernateUtilities.getSessionFactory().close();
}

private static void PopulateSampleData() {
    Session session = HibernateUtilities.getSessionFactory().openSession();
    session.beginTransaction();

    User joe = CreateUser("Joe", 500, 50, "Good job", "You made it!");
    session.save(joe);

    User bob = CreateUser("Bob", 300, 20, "Taco time!");
    session.save(bob);

    User amy = CreateUser("Amy", 250, 200, "Yes!!!");
    session.save(amy);

    session.getTransaction().commit();
    session.close();
}

private static User CreateUser(String name, int goal, int total, String... alerts) {
    User user = new User();
    user.setName(name);
    user.getProtienData().setGoal(goal);
    user.addHistory(new UserHistory(new Date(), "Set goal to " + goal));
    user.getProtienData().setTotal(total);
    user.addHistory(new UserHistory(new Date(), "Set total to " + total));
    for (String alert : alerts) {
        user.getGoalAlerts().add(new GoalAlert(alert));
    }
    return user;
}
}

Answer 1

我怀疑criteria.list()正在返回List<Integer>而不是List<Object[]>，因为提取了一列。尝试更改

List<Object[]> results = criteria.list();

到

List<Integer> results = criteria.list();

将单个投影添加到条件查询

1 个答案: