Java JPA 双向多对一映射不起作用

Question

我正在尝试在现有表和新表之间设置一个新的 JPA 双向映射。 它似乎不起作用。 实体管理器在运行时不会初始化。

其他现有表似乎没有问题。 此外，如果我从持久性 xml 中删除此新表及其关联的 object，则该应用程序启动正常。

该应用程序也可以正常工作，当新表自己添加时，没有外键连接即。 OneToMany 或 ManyToOne 映射。

有人可以帮我确定缺少什么吗？

例外指出：

ERROR SomeService:104 - General Error: Something wrong happened in JVM
java.lang.NoClassDefFoundError: Could not initialize class com.java.path.persistence.DefaultEntityManager

CREATE TABLE IF NOT EXISTS new_entity (
    id                      BIGSERIAL PRIMARY KEY,
    existing_tbl_id         BIGINT NOT NULL
);

现有实体：

CREATE TABLE IF NOT EXISTS existing_entity (
    id                      BIGSERIAL PRIMARY KEY
);

现有实体.java

@Entity
@Table(name = "existing_entity")
public class ExistingEntity {
   @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    private Long id;

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }

    @OneToMany(mappedBy = "existingEntity", 
            cascade = CascadeType.ALL, 
            fetch = FetchType.EAGER)
    private List<NewEntity> newEntities = new ArrayList<>();


    public List<NewEntity> getNewEntities() {
        return newEntities;
    }

    public void setNewEntities(List<NewEntity> newEntities) {
        newEntities.forEach(newEntity -> 
        newEntity.setExistingEntity(this)
        );
        this.newEntities = newEntities;
    }

    public void addNewEntities(NewEntity newEntity) {
        if (newEntity != null) {
            newEntity.setExistingEntity(this);
            newEntities.add(newEntity);
        }
    }
}

新实体.java

@Entity
@Table(name = "new_entity")
public class NewEntity {
   @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    private Long id;

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "existing_tbl_id")
    private ExistingEntity existingEntity;

    public ExistingEntity getExistingEntity() {
        return existingEntity;
    }

    public void setExistingEntity(ExistingEntity existingEntity) {
        this.existingEntity = existingEntity;
    }

}

我也尝试了以下方法，但它不起作用：

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "existing_tbl_id", referencedColumnName = "id")
    private ExistingEntity existingEntity;

Answer 1

解决方案：将 Fetch 类型切换为 Lazy，如下所示：

    @OneToMany(mappedBy = "existingEntity", 
    cascade = CascadeType.ALL, 
    fetch = FetchType.LAZY)
    private List<NewEntity> newEntities = new ArrayList<>();

我不确定 fetch 样式如何导致这种差异。