Jackson 序列化期间子对象为空？

Question

我捕获了 json 响应，我发现它是

{"page":"1","total":"2","records":"15","rows":[{"id":1,"firstName":"John","lastName":"Smith","username":"john","password":"21232f297a57a5a743894a0e4a801fc3","role":null},{"id":2,"firstName":"Jane","lastName":"Adams","username":"jane","password":"ee11cbb19052e40b07aac0ca060c23ee","role":null},

My User 和 Role 类，非常简单，所以我想我一定忽略了一些琐碎的事情。

@Entity(name="user")
public class User implements Serializable {
    
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    
    private String firstName;
    private String lastName;
    
    @Column(unique=true)
    private String username;
    private String password;
    
    @JsonIgnore
    @OneToMany(mappedBy="user", cascade={CascadeType.PERSIST, CascadeType.MERGE},fetch =FetchType.EAGER)
    private List<Role> roles =  new ArrayList<Role>();
    
    
    public List<Role> getRoles() {
        return roles;
    }

    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }

    
    @ManyToOne
    private Role role;

    public User() {}
    
    public User(String username, String password, String firstName, String lastName, Role role) {
        this.username = username;
        this.password = password;
        this.firstName = firstName;
        this.lastName = lastName;
        this.role = role;
    }
    
    public User(String username, String firstName, String lastName, Role role) {
        this.username = username;
        this.firstName = firstName;
        this.lastName = lastName;
        this.role = role;
    }

    public User(String username) {
        this.username = username;
    }
    
    public Long getId() {
        return id;
    }

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

    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;
    }

    public String getUsername() {
        return username;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Role getRole() {
        return role;
    }

    public void setRole(Role role) {
        this.role = role;
    }
}

@Entity(name="role")
public class Role  implements Serializable{
    
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    
    @JsonIgnore
    @ManyToOne
    @JoinColumn (name = "user_id", nullable= true)
    private User user;
    private Integer role;
    
    public Role() {}
    
    public Role(Integer role) {
        this.role = role;
    }
    
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    public Integer getRole() {
        return role;
    }
    public void setRole(Integer role) {
        this.role = role;
    }
}

我还尝试了

@JsonUnwrapped @ManyToOne private Role role;

但这更糟糕，因为在这种情况下我的 json 根本没有该角色。

{"id":1,"firstName":"约翰","lastName":"史密斯","用户名":"约翰","密码":"21232f297a57a5a743894a0e4a801fc3"},

Answer 1

由于复杂的遗留关系要求，即用户具有一个和多个角色，在将其作为响应传回之前，我错误地操作了该对象。

@JsonUnwrapped 仅当子对象中有属性时才能展开，因此它按预期工作。