JPA 异常：org.hibernate.MappingException：无法确定类型答案

【问题标题】：JPA Exceptions: org.hibernate.MappingException: Could not determine type forJPA 异常：org.hibernate.MappingException：无法确定类型
【发布时间】：2021-01-06 13:34:15
【问题描述】：

我在User 和Items 表之间创建了One to many 关系。下面是sql 和java 代码。我收到异常原因：

org.hibernate.MappingException`：无法确定类型：com.model.Users，在表：项目，列：[org.hibernate.mapping.Column(users)]

请帮忙绘制地图。

    CREATE TABLE users
    ( id integer NOT NULL DEFAULT nextval('userseq'::regclass),
      email character varying(64) NOT NULL,
      passwords character varying(64) NOT NULL
      CONSTRAINT users_pkey PRIMARY KEY (id)
    )
  
    CREATE TABLE items
    ( id integer NOT NULL DEFAULT nextval('itemseq'::regclass),
      userid integer NOT NULL,
      itemname character varying(4096) NOT NULL,
      CONSTRAINT message_pkey PRIMARY KEY (id),
      CONSTRAINT userid_fkey FOREIGN KEY (userid)
      REFERENCES users (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
     )

       public class Users  {
        private Items items;
            
            @OneToMany(targetEntity=Items.class, mappedBy="users", fetch=FetchType.LAZY)  //sender is message(c)filed
            public List<Items> getItems() {
                return items;
            }
        }
        
        @ManyToOne(fetch = FetchType.LAZY, targetEntity = Users.class)
            @JoinColumn(name = "userid", nullable = false)            // sendid is database column
            public Users getUsers() {
                return users;
            }

原因：org.springframework.beans.factory.BeanCreationException：创建名为“jpaMappingContext”的bean时出错：调用init方法失败；嵌套异常是 javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory;嵌套异常是 org.hibernate.MappingException：无法确定类型：com.model.Users，在表：项目，列：[org.hibernate.mapping.Column(users)]

原因：javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory;嵌套异常是 org.hibernate.MappingException：无法确定类型：com.model.Users，在表：项目，列：[org.hibernate.mapping.Column(users)]

原因：org.hibernate.MappingException：无法确定类型：java.util.List，表：用户，列：[org.hibernate.mapping.Column(items)]

【问题讨论】：

请同时添加Item实体。

标签： java postgresql spring-boot hibernate jpa

【解决方案1】：

Users 类不应该有一个项目列表吗？试试下面的，

@Entity
@Table(name = "users")
public class Users{

    @OneToMany(mappedBy = "user")
    private List<Items> items;

}

@Entity
@Table(name = "items")
public class Items{

    @JoinColumn(name="userid")
    @ManyToOne
    private User user;

}

【讨论】：