Question

美好的一天。我尝试使用持久性api具有多对多的依赖关系。我填写一个新的用户数据并尝试将其添加到数据库，但得到一个例外：

Exception Description: [class main.java.entities.User] uses a non-entity [class main.java.entities.UserAccounts] as target entity in the relationship attribute [field accounts].

我尝试在name部分使用@ManyToMany注释的差异值，例如bank_user_accounts和userAccounts。第二个值是persistence.xml中的单位名称。但这种麻烦仍然存在。

用户类：

@Entity(name="bank_users")
public class User {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  @ManyToMany
  @JoinTable(
      name = "bank_user_accounts",
      joinColumns = @JoinColumn(name = "user_id"),
      inverseJoinColumns = @JoinColumn(name = "account_id")
  )
  private List<UserAccounts> accounts;
}

UserAccounts类：

@Entity(name="bank_user_accounts")
public class UserAccounts {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  @Column(name = "user_id")
  private int userId;

  @Column(name = "account_id")
  private int accountId;
}

的persistence.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
             version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
  <persistence-unit name="users" transaction-type="RESOURCE_LOCAL">
    <class>main.java.entities.User</class>
    <properties>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
      <property name="javax.persistence.jdbc.url" value="deleted" />
      <property name="javax.persistence.jdbc.user" value="deleted" />
      <property name="javax.persistence.jdbc.password" value="deleted" />
    </properties>
  </persistence-unit>

  <persistence-unit name="userAccounts" transaction-type="RESOURCE_LOCAL">
    <class>main.java.entities.UserAccounts</class>
    <properties>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
      <property name="javax.persistence.jdbc.url" value="deleted" />
      <property name="javax.persistence.jdbc.user" value="deleted" />
      <property name="javax.persistence.jdbc.password" value="deleted" />
    </properties>
  </persistence-unit>

</persistence>

Answer 1

User和UserAccounts之间的关系，而不是@OneToMany，或者只是一个可嵌入的类。

@ManyToMany应该在双方都有注释（双向），并且应该在一侧设置mappedBy属性，以指向引用此实体作为集合的另一方的属性名称。

Answer 2

我在您的代码中观察到的一件事是您在User类中使用了许多非常规的注释，但您还没有在userAccounts类中使用过。要实现ManyToMany关系，两个实体都应使用ManyToMany进行注释。

Answer 3

问题是（尽管可能已过时）您有一个持久性单元到另一个持久性单元的引用。您可以轻松地将两者放在同一个单位：

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
             version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
  <persistence-unit name="users" transaction-type="RESOURCE_LOCAL">
    <class>main.java.entities.User</class>
    <class>main.java.entities.UserAccounts</class>
    <properties>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
      <property name="javax.persistence.jdbc.url" value="deleted" />
      <property name="javax.persistence.jdbc.user" value="deleted" />
      <property name="javax.persistence.jdbc.password" value="deleted" />
    </properties>
  </persistence-unit>
</persistence>

Java Persistence api：class在关系属性中使用非实体类作为目标实体

3 个答案: