Hibernate mappedBy和@JoinColumn

Question

当我试图得到一对多，多到一的关系时，我遇到了车辆表中联接列的问题。为什么hibernate要搜索列USER_ID而不是将它加入到表中？我知道加入的目的，但是当我试图将它与映射属性一起使用时，我得到了这个错误。那密码怎么了？

我得到的例外是：

原因：“字段列表”中的com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException:未知列“USER_ID”

用户表：

@Entity
@Table(name = "users")
public class User {

public User(){}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getFirst_name() {
    return first_name;
}

public void setFirst_name(String first_name) {
    this.first_name = first_name;
}

public int getSalary() {
    return salary;
}

public void setSalary(int salary) {
    this.salary = salary;
}

public String getLast_name() {
    return last_name;
}

public void setLast_name(String last_name) {
    this.last_name = last_name;
}

@Override
public String toString() {
    return "User{" +
            "id=" + id +
            ", first_name='" + first_name + '\'' +
            ", salary=" + salary +
            ", last_name=" + last_name +
            '}';
}

public Collection<Vehicle> getVehicles() {
    return vehicles;
}

public void setVehicles(Collection<Vehicle> vehicles) {
    this.vehicles = vehicles;
}

@OneToMany(mappedBy = "user")
private Collection<Vehicle> vehicles = new ArrayList<>();

public Collection<Address> getAddresses() {
    return addresses;
}
public void setAddresses(Collection<Address> addresses) {
    this.addresses = addresses;
}

    @ElementCollection // for saving the collection or persist it to database
    @JoinTable(joinColumns = @JoinColumn(name = "fk_user_id")) // will add to the fk created table renamed column "fk_user_id"
    private Collection<Address> addresses = new ArrayList<>();

    @Id
    @Column(name = "user_id")
    private int id;
    @Column(name = "first_name")
    private String first_name;
    @Column(name = "salary")
    private int salary;
    @Column(name = "last_name")
    private String last_name;
 }

车辆：

@Entity
@Table(name = "vehicle")
public class Vehicle {

public User getUser() {
    return user;
}

public void setUser(User user) {
    this.user = user;
}

@ManyToOne
@JoinColumn(name = "USER_ID")
private User user;

public int getVehicle_id() {
    return vehicle_id;
}

public void setVehicle_id(int vehicle_id) {
    this.vehicle_id = vehicle_id;
}

public String getVehicle_name() {
    return vehicle_name;
}

public void setVehicle_name(String vehicle_name) {
    this.vehicle_name = vehicle_name;
}

@Id
private int vehicle_id;
private String vehicle_name;

}

Answer 1

你对@JoinColumn的态度和你想的有点不同。

当您有一个配置时：

public class Vehicle {

  @ManyToOne
  @JoinColumn(name = "USER_ID")
  private User user;

它告诉持久性提供程序在连接VEHICLE.USER_ID表和USERS表时使用VEHICLE列。

默认情况下，在USERS表端使用主键，在本例中，主键是一个名称相同的列：USERS.USER_ID (除非您显式地指定referencedColumnName属性i( @JoinColumn) )。

底线是您需要在您的车辆表中有一个user_id列。