如何將多個單一對多關聯在Hibernate中

Question

映射我有這些3代表在我的數據庫

CREATE TABLE IF NOT EXISTS `User`(
    `id`  INT    NOT NULL AUTO_INCREMENT, 
    `name`  VARCHAR(255) NOT NULL DEFAULT '', 
    PRIMARY KEY (`id`) 
) 

CREATE TABLE IF NOT EXISTS `Project` (
    `id`  INT    NOT NULL AUTO_INCREMENT, 
    `manager` INT    NOT NULL, 
    `name`  VARCHAR(255) NOT NULL DEFAULT '', 
    PRIMARY KEY (`id`), 
    FOREIGN KEY (`manager`) REFERENCES `User`(`id`) 
) 

CREATE TABLE IF NOT EXISTS `Work`(
    `id`   INT    NOT NULL AUTO_INCREMENT, 
    `project_id` INT    NOT NULL DEFAULT -1, 
    `name`   VARCHAR(255) NOT NULL DEFAULT '', 
    PRIMARY KEY (`id`), 
    FOREIGN KEY (`project_id`) REFERENCES `Project`(`id`), 
    FOREIGN KEY (`creator`)  REFERENCES `User`(`id`) 
) 

然後我想用Hibernate將它們連接起來。

這是我的java類

用戶：

// ... import code 
@Entity 
@Table 
public class User { 
    @Id 
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private int id; 
    @Column 
    private String name; 

    @OneToMany(mappedBy = "manager") 
    private List<Project> projects; 

    public User() { 
    } 
    // ... Getter & Setter code 
} 

項目：

// ... import code 
@Entity 
@Table 
public class Project { 
    @Id 
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private int id; 
    @Column 
    private String name; 

    @ManyToOne 
    @JoinColumn(name = "manager") 
    private User manager; 

    public Project() { 
    } 
    // ... Getter & Setter code 
} 

工作：

// ... import code 
public class Work { 
    @Id 
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private int id; 
    @Column 
    private String name; 
    @Column(name = "project_id") 
    private int projectId; 

    @ManyToOne 
    @JoinColumn(name = "creator") 
    private User creator; 

    public Work() { 
    } 
    // ... Getter & Setter code 
} 

現在它可以工作。

但是，在項目和工作（一對多/多對一）映射關係之後，它給了我錯誤消息。

我映射做的是：

添加這些代碼到工程類：

@OneToMany(mappedBy = "project_id") 
private List<Work> works; 

public List<Work> getWorks() { 
    return works; 
} 

public void setWorks(List<Work> works) { 
    this.works = works; 
} 

而且這些代碼到工作類：

@ManyToOne 
@JoinColumn(name = "project_id") 
private Project project; 
public Project getProject() { 
    return project; 
} 

public void setProject(Project project) { 
    this.project = project; 
} 

，並刪除@Column(name = "project_id") private int projectId;

然後它給了我錯誤信息：

Exception in thread "main" org.hibernate.AnnotationException: mappedBy reference an unknown target entity property: database.tables.Work.project_id in database.tables.Project.works 
    at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:768) 
    at org.hibernate.cfg.annotations.CollectionBinder$1.secondPass(CollectionBinder.java:728) 
    at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:70) 
    at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1697) 
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1426) 
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1846) 

所以我想知道如何映射項目工作的關係。

Answer 1

在 '工程' 類，代碼：

@OneToMany(mappedBy = "project_id") 
private List<Work> works; 

而且，在 '工作' 類，代碼：

@ManyToOne 
@JoinColumn(name = "project_id") 
private Project project; 
//var name should match with mappedBy name in other class 

中的名稱（'的mappedBy =」 project_id「）和其他類（私人項目項目）中的變量名稱都應匹配。