java - OneToOne 对象为空

Question

我正在使用 play 框架 (v2.3.1)，并且我有 2 个模型对象；用户和位置。他们彼此之间存在一对一的关系。保存按预期进行，但是当我想从数据库中检索用户时，该位置为空。

我的类(class):

@Entity
public class Location extends Model
{
    public static Finder<Long, Location> find = new Finder<Long, Location>(Long.class, Location.class);

    @OneToOne
    @Id
    public Long id;

    @Constraints.Required
    @Formats.NonEmpty
    public String name;

    public Location(String name)
    {
        this.name = name;
    }

    @Override
    public String toString()
    {
        return id+":"+name;
    }
}

@Entity
public class User extends Model
{
    public static Finder<Long, User> find = new Finder<Long, User>(Long.class, User.class);

    @Id
    public Long id;

    @Constraints.Required
    @Formats.NonEmpty
    @Column(unique = true)
    public String email;

    public String name;

    @OneToOne
    @PrimaryKeyJoinColumn(name = "id", referencedColumnName = "location_id")
    public Location location;

    public User(String email, String name, Location location)
    {
        this.email = email;
        this.name = name;
        this.location = location;
    }

    public static User getByEmail(String email)
    {
        return find.where().eq("email", email).findUnique();
    }   
}


public class Application extends Controller {

    public static Result index() 
    {
        User user = User.getByEmail("random@mail.com");     
        return ok( user.name + "\t" + user.location );
    }   
}

示例输出为:Some Person 2:null

已收到位置 ID，但名称变量具有空值。获取用户后如何获取要填充的位置对象？

Answer 1

默认情况下，所有关系都会被延迟加载。这意味着，所有实体引用(来自另一个表的实体引用默认情况下不会加载( FetchType.LAZY ))。所以你应该指定你想要急切地加载它。像这样

@OneToOne(fetch=FetchType.EAGER)