如何在春季使用休眠将对象列表映射到表中？答案

【问题标题】：How to map a list of Objects into a table with hibernate in spring?如何在春季使用休眠将对象列表映射到表中？
【发布时间】：2016-12-10 16:49:12
【问题描述】：

我正在尝试将用户列表映射到位置对象，但出现映射异常。这是因为 List 对象不被数据库识别？或者为什么我会得到这个异常？

这是我的用户类：

@Entity
@Table(name = "users")
public class NewUser extends BaseEntity{
    private String login;
    private String fullName;

    private Location location;
    private Department department;
    private Role role;
    private Long days;
    private String team;
    private Long managerId;
    private String hiredDate;

    public String getLogin() {
        return login;
    }

    public void setLogin(String login) {
        this.login = login;
    }

    public String getFullName() {
        return fullName;
    }

    public void setFullName(String fullName) {
        this.fullName = fullName;
    }

    public Location getLocation() {
        return location;
    }

    @ManyToOne(targetEntity = Location.class)
    @JoinTable(name = "location")
    public void setLocation(Location location) {
        this.location = location;
    }

    public Department getDepartment() {
        return department;
    }

    @ManyToOne(targetEntity = Department.class)
    public void setDepartment(Department department) {
        this.department = department;
    }

    public Role getRole() {
        return role;
    }

    @ManyToOne(targetEntity = Role.class)
    @JoinTable(name = "role")
    public void setRole(Role role) {
        this.role = role;
    }

和位置类：

@Entity
@Table(name = "location")
public class Location extends BaseEntity{
    private List<NewUser> users;

    public List<NewUser> getUsers() {
        return users;
    }

    @OneToMany(targetEntity = NewUser.class, mappedBy = "location")
    @JoinTable(name = "users")
    public void setUsers(List<NewUser> users) {
        this.users = users;
    }
}

基础实体：

@MappedSuperclass
public abstract class BaseEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    public long getId() {
        return id;
    }

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

错误是：

Caused by: org.hibernate.MappingException: Could not determine type for: java.util.List, at table: location, for columns: [org.hibernate.mapping.Column(users)]

如何使用hibernate注解有效地进行关系映射？

【问题讨论】：

标签： java spring hibernate

【解决方案1】：

您的映射不正确。假设您希望用户表中的 FK 指向相应的位置，然后使用以下命令：

在用户中

@ManyToOne
@JoinColumn(name = "location_id")
public void setLocation(Location location) {
    this.location = location;
}

在位置

@OneToMany(mappedBy = "location")
public void setUsers(List<NewUser> users) {
    this.users = users;
}

如果您不希望用户表中位置的外键，那么您可以使用连接表“user_locations”与列 user_id（FK 到用户）和 location_id（FK 到位置）并使用 @JoinTable 注释相应地指定它。在您的映射中，这看起来像：

@ManyToOne
@JoinTable(name = "user_locations", joinColumns = @JoinColumn(name="user_id"), inverseJoinColumns = @JoinColumn(name = "location_id"))
public void setLocation(Location location) {
    this.location = location;
}

【讨论】：

【解决方案2】：

Hibernate 已经知道每个实体的表，因为您正在使用 @Table 注释指定它。您正在建立两个独立的关系，而不是双边关系。

使用mappedBy，声明您要依赖的其他实体的字段：

Location.java

@OneToMany(fetch=FetchType.LAZY, cascade = {CascadeType.ALL}, mappedBy="location")
public List<NewUser> getUsers() {
    return users;
}

NewUser.java

@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="id_user")
public Location getLocation() {
    return location;
}

另请参阅：

【讨论】：

感谢@AlanHay，实际上是拥有关系的用户实体。