Spirng一对多关系引发异常：org.springframework.http.converter.HttpMessageNotWritableException

Question

我尝试使用spring在两个实体之间创建简单的关系。有一个User实体拥有许多profile实体。

用户实体

@Entity
public class User {

    @OneToMany(mappedBy = "user")
    private List<Profile> profiles;

    public List<Profile> getProfiles() {
        return profiles;
    }

    public void setProfiles(List<Profile> profiles) {
        this.profiles = profiles;
    }
}

个人资料实体

@Entity
public class Profile {

    @ManyToOne
    @JoinColumn(name = "user_id", nullable = false)
    private User user;

    public User getUser() {
        return user;
    }

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

[当我尝试在this.profileRepository.findById(id).get()中找到带有@RestController的配置文件时，出现此错误：

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: User.profiles, could not initialize proxy - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: User.profiles, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->User["profiles"])]
The server encountered an unexpected condition that prevented it from fulfilling the request.

有人可以向我解释为什么这行不通吗？我遵循了this教程。

Answer 1

如果您知道每次检索用户都希望查看所有配置文件，然后将字段注释更改为：

@OneToMany(fetch = FetchType.EAGER, mappedBy = "user", cascade =CascadeType.ALL
private List<Profile> profiles; = new LinkedHashSet<Profile>();

默认情况下，集合是延迟加载的，如果想了解更多，请查看this。