java - Hibernate ManyToOne，连接表中的重复键

Question

我的数据库中有三张表，一张用于房屋，一张用于用户。在这种情况下，用户可以拥有很多房子。

每个 House 都有一个唯一生成的 ID(PK)。用户的用户名是 Id(PK)。用户在他们的类(class)中有一个包含房屋对象的集合。

假设用户 foo 添加了 3 个拥有 key 的 houes； 1、2、3，然后用户栏继续添加带有 key 1 的房子，然后出现 hibernate 错误，提示我有重复的 key 。

sep. 28, 2015 2:06:00 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Duplicate entry '1' for key 'UK_r5dofs84kmj9k4a73t03avcce'
sep. 28, 2015 2:06:00 PM org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl release
INFO: HHH000010: On release of batch it still contained JDBC statements

我正在研究ManyToMany，以及一些人是如何做到这一点的。但注意到我的家庭类也有一个与用户的集合。这在我的代码中根本没有任何功能。

下面是我的两个类(class)。

用户类别

@Entity
public class User {

@Id
private String username;
private String firstname;
private String lastname;

@OneToMany(fetch=FetchType.EAGER)
private Collection<Houses> houses = new ArrayList<>();

public User() {
}

public User(String username) {
    this.username = username;
}

public Collection<Houses> getHouses() {
    return houses;
}

public void setHouses(Collection<Marker> houses) {
    this.houses = houses;
}

public String getUsername() {
    return username;
}

public void setUsername(String username) {
    this.username = username;
}

public String getFirstname() {
    return firstname;
}

public void setFirstname(String firstname) {
    this.firstname = firstname;
}

public String getLastname() {
    return lastname;
}

public void setLastname(String lastname) {
    this.lastname = lastname;
}
}

房屋等级

@Entity
@Table(name="house")
public class House{


    private String address; 

    @Id  @GeneratedValue(strategy=GenerationType.AUTO)
    private long projectId; 

    public House() {

    }

    public House(String address) {
        this.address = address;
    }

    public long getProjectId() {
        return projectId;
    }

    public void setProjectId(long projectId) {
        this.projectId = projectId;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

我不知道可能出了什么问题，这是 OneToMany 关系，我错了吗？

Answer 1

您的多对多想法是正确的方法，因为您遇到的情况是一栋房子可以属于多个用户，而一个用户可以拥有多栋房子。所以我会创建类似的东西:User.java

//...
@ManyToMany
@JoinTable(name = "house_user_association", joinColumns = {
        @JoinColumn(name = "username", referencedColumnName = "username")},
        inverseJoinColumns = {@JoinColumn(name = "house_id", referencedColumnName = "projectId")})
private Set<House> houses = new HashSet<>();
//...

House.java

//...
@ManyToMany(mappedBy = "houses")
private Set<User> users = new HashSet<>();
//...

一切都应该运行良好。

它将创建一个连接表来映射您的实体星座。

编辑对于您需要的独特的多对多User.java

//...
@ManyToMany
@JoinTable(name = "house_user_association", joinColumns = {
        @JoinColumn(name = "username", referencedColumnName = "username")},
        inverseJoinColumns = {@JoinColumn(name = "house_id", referencedColumnName = "projectId"),
        uniqueConstraints = { @UniqueConstraint(columnNames = { "username", "house_id"})
private Set<House> houses = new HashSet<>();
//...