One-To-Many in JPA

最新推荐文章于 2024-02-23 23:06:55 发布

最新推荐文章于 2024-02-23 23:06:55 发布 · 95 阅读

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#JPA #Java

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本文展示了一个使用Java实现的实体关系映射示例，包括父对象(ParentObject)与子对象(ChildObject)之间的多对一及一对多关系。通过@Entity注解定义实体类，并利用@OneToMany和@ManyToOne注解建立实体间的关联。

@Entity
@Table(name = "UT_PARENT")
public class ParentObject {
    private int id;
    private String value;
    private Set<ChildObject> children;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "ID", precision = 19, scale = 0)
    public int getId() {
        return id;
    }

    //mappedBy refer to the property name of Child.parent
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity=ChildObject.class, mappedBy="parentObject")
    public Set<ChildObject> getChildren() {
        return children;
    }
}

@Entity
@Table(name = "UT_CHILD")
public class ChildObject {
    private int id;
    private String value;
    private ParentObject parentObject;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "ID", precision = 19, scale = 0)
    public int getId() {
        return id;
    }

    @ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, targetEntity=ParentObject.class)
    @JoinColumn(name = "UT_PRAENT_ID", insertable = false, updatable = false)
    public ParentObject getParentObject() {
        return parentObject;
    }
}