Java 如何在休眠中通过 ArrayList 保存多个对象？
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How to save multiple objects via ArrayList in hibernate?
提问by Hadrian Blackwater
I have a Student entity. My idea is to collect multiple student objects in an ArrayList and save all objects from that list to the database. When do you use @ElementCollection annotation? Does it apply to situations like this?
我有一个学生实体。我的想法是在 ArrayList 中收集多个学生对象并将该列表中的所有对象保存到数据库中。什么时候使用@ElementCollection 注解？它适用于这样的情况吗？
Student:
学生：
package basic;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
@Entity
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String name;
public Student() {
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
public Student(String name) {
this.name = name;
}
}
Runner:
赛跑者：
package basic;
import java.util.ArrayList;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class Runner {
public static void main(String[] args) {
SessionFactory sessionFactory = new Configuration().configure("/basic/hibernate.cfg.xml").buildSessionFactory();
Session session = sessionFactory.openSession();
session.beginTransaction();
List<Student> students = new ArrayList<>();
students.add(new Student("Michael"));
students.add(new Student("Dave"));
students.add(new Student("Tom"));
students.add(new Student("Dinesh"));
students.add(new Student("Lakshman"));
students.add(new Student("Cruise"));
session.save(students);
session.getTransaction().commit();
session.close();
}
}
Error
错误
Exception in thread "main" org.hibernate.MappingException: Unknown entity: java.util.ArrayList
at org.hibernate.metamodel.internal.MetamodelImpl.entityPersister(MetamodelImpl.java:620)
at org.hibernate.internal.SessionImpl.getEntityPersister(SessionImpl.java:1596)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:104)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:192)
at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:38)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:177)
at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:32)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:668)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:660)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:655)
at basic.Runner.main(Runner.java:27)
采纳答案by ByeBye
You have to do something like this:
你必须做这样的事情：
for(Student student : students) {
session.save(student);
}
If you want to save entity you should map it. ArrayList<> is not mapped entity. Student has mapping so you should save it separately.
如果你想保存实体，你应该映射它。ArrayList<> 不是映射实体。学生有映射所以你应该单独保存它。
回答by Rafal Mikolajczuk
@ElementCollection you should use to define relation between object - here you have nice explenation https://en.wikibooks.org/wiki/Java_Persistence/ElementCollection
@ElementCollection 你应该用来定义对象之间的关系 - 在这里你有很好的解释https://en.wikibooks.org/wiki/Java_Persistence/ElementCollection
To save list of object, you need to iterate by objects, something like this -> How to insert multiple rows into database using hibernate?
要保存对象列表，您需要按对象进行迭代，就像这样->如何使用休眠将多行插入到数据库中？
