JPA 多对多关系创建两个连接表

Question

我正在尝试在 User 和 FileObject 类之间创建多对多关系，假设用户可以访问许多文件对象，文件对象可以通过以下方式访问许多用户和一对多关系，因为一个用户可以拥有多个文件，但一个文件只能由一个用户拥有。这是我的代码：

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    public int id;
    public String firstname;
    public String lastname;
    public String publicAttributes;
    public String privateAttributes;

    @ManyToOne
    private Department department;

    @OneToMany(mappedBy = "user")
    public List<Device> devices = new ArrayList<Device>();

    @OneToMany(mappedBy = "userCreator")
    public List <FileObject> fileOwned = new ArrayList <FileObject>();

    @ManyToMany
    @JoinTable(name="USER_FILE_ACCESS")
    public List<FileObject> fileHasAccess = new ArrayList<FileObject>();
}

@Entity
public class FileObject {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    public int id;
    String checksum;

    @OneToMany(mappedBy = "fileObject")
    public List<Policy> policies = new ArrayList<Policy>();

    byte[] encryptedFileKey;

    byte[] iv;

    @ManyToOne
    public User userCreator;

    @ManyToMany
    public List<User> listUserAccessor = new ArrayList<User>();
}

理论上它应该只创建一个连接 table 即 USER_FILE_ACCESS 但是当我运行脚本然后它创建两个连接 table 我不确定为什么。

以下是 SQL 命令的摘录：

show tables;
+------------------+
| Tables_in_cpabe  |
+------------------+
| DEPARTMENT       |
| DEVICE           |
| FILEOBJECT       |
| FILEOBJECT_USER  |
| POLICY           |
| SEQUENCE         |
| USER             |
| USER_FILE_ACCESS |
+------------------+

show columns from FILEOBJECT_USER;
+---------------------+---------+------+-----+---------+-------+
| Field               | Type    | Null | Key | Default | Extra |
+---------------------+---------+------+-----+---------+-------+
| FileObject_ID       | int(11) | NO   | PRI | NULL    |       |
| listUserAccessor_ID | int(11) | NO   | PRI | NULL    |       |
+---------------------+---------+------+-----+---------+-------+

show columns from USER_FILE_ACCESS;
+------------------+---------+------+-----+---------+-------+
| Field            | Type    | Null | Key | Default | Extra |
+------------------+---------+------+-----+---------+-------+
| User_ID          | int(11) | NO   | PRI | NULL    |       |
| fileHasAccess_ID | int(11) | NO   | PRI | NULL    |       |
+------------------+---------+------+-----+---------+-------+

如何让 join table 成为唯一一个 table？

Answer 1

如果你想建立 bi-directional 关系，那么：

@Entity
public class User {

@ManyToMany
@JoinTable(name="USER_FILE_ACCESS"
     joinColumns=@JoinColumn(name="user_id"),
        inverseJoinColumns=@JoinColumn(name="fileHasAccess_ID "))
public Set<FileObject> fileHasAccess;


@Entity
public class FileObject {

@ManyToMany
@JoinTable(name="USER_FILE_ACCESS"
         joinColumns=@JoinColumn(name="fileHasAccess_ID"),
            inverseJoinColumns=@JoinColumn(name="user_id"))
    public Set<User> listUserAccessor;

更新

尝试使用 SEt 而不是列表。

您也可以尝试另一个 bi-directional 选项。因此，在参考侧或反向侧（non-owning 侧），您将映射如下：

@ManyToMany(mappedBy = "fileHasAccess")
public Set<User> listUserAccessor;

此外，double-check 列名..我可能放了一些与您在数据库中实际拥有的不同的东西。

JPA 多对多关系创建两个连接表

JPA Many to Many Relationship Creates Two Join Tables

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