Question

我正在使用Spring Boot和Hibernate开展一个休息项目，目前正在尝试弄清楚如何处理我的json序列化。

上面的ERD中显示的模式由Hibernate映射并且工作正常。

当我向控制器发出get请求时出现问题。我的理解是Spring现在尝试使用Jackson序列化对象链。因为父对象和子对象都有另一个作为属性，所以我们发现自己遇到了无限递归循环。

现在我已经研究过@JsonIgnore，@ JsonView，@ JasonManagedReference和@JsonBackReference，但这些似乎只适用于一对多的关系。

我正在寻找的是一种情况，例如当我向/users/{id}发出GET请求时，我得到的用户对象包括它的所有关系属性（让我们称之为完整对象），但这种关系属性本身不显示它们的关系属性（最小化对象）。这适用于上面提到的注释，但我如何以其他方式使这项工作？

对所需的回复：/users/{id}

{   // full user object
    id: 1,
    username: 'foo',
    // password can be JsonIgnored because of obvious reasons
    role: { // minimized role object
        id: 1,
        name: 'bar'
        // NO USERS LIST
    }
    area: { //minimized area object
        id: 2,
        name: 'some val'
        // NO USERS LIST
        // NO TABLES LIST
    }
}

/userrole/{id}

的所需回复

{ // full role object
    id: 1,
    name: 'waiter'
    users: [
        {   // minmized user object
            id: 1,
            username: 'foo'
            // password can be JsonIgnored because of obvious reasons
            // NO ROLE OBJECT
            // NO AREA OBJECT
        },
        {   // minmized user object
            id: 1,
            username: 'foo'
            // password can be JsonIgnored because of obvious reasons
            // NO ROLE OBJECT
            // NO AREA OBJECT
        }
    ]
}

一般情况下：当直接向实体发出请求时，我想要一个完整的对象，当间接请求时，我想要一个最小化的对象。

任何想法？我希望我的解释足够清楚。

更新

区域，用户和用户角色POJO在评论部分中的要求。

用户

@Entity
@Table(name = "users", schema = "public", catalog = "PocketOrder")

public class User {
    private int id;
    private String username;
    private String psswrd;
    private List<Area> areas;

    private UserRole Role;

    @Id
    @Column(name = "id", nullable = false)
    public int getId() {
        return id;
    }

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

    @Basic
    @Column(name = "username", nullable = false, length = 20)
    public String getUsername() {
        return username;
    }

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

    @Basic
    @JsonIgnore
    @Column(name = "psswrd", nullable = true, length = 40)
    public String getPsswrd() {
        return psswrd;
    }

    public void setPsswrd(String psswrd) {
        this.psswrd = psswrd;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        User user = (User) o;

        if (id != user.id) return false;
        if (username != null ? !username.equals(user.username) : user.username != null) return false;
        if (psswrd != null ? !psswrd.equals(user.psswrd) : user.psswrd != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = id;
        result = 31 * result + (username != null ? username.hashCode() : 0);
        result = 31 * result + (psswrd != null ? psswrd.hashCode() : 0);
        return result;
    }

    @ManyToMany(mappedBy = "users")
    public List<Area> getAreas() {
        return areas;
    }

    public void setAreas(List<Area> areas) {
        this.areas = areas;
    }

    @ManyToOne
    @JoinColumn(name = "role_fk", referencedColumnName = "id", nullable = false)
    public UserRole getRole() {
        return Role;
    }

    public void setRole(UserRole role) {
        Role = role;
    }
}

的UserRole

@Entity
@javax.persistence.Table(name = "userroles", schema = "public", catalog = "PocketOrder")
public class UserRole {
    private int id;
    private String name;
    private List<User> users;


    @Id
    @Column(name = "id", nullable = false)
    public int getId() {
        return id;
    }

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

    @Basic
    @Column(name = "name", nullable = false, length = 20)
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        UserRole userRole = (UserRole) o;

        if (id != userRole.id) return false;
        if (name != null ? !name.equals(userRole.name) : userRole.name != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = id;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        return result;
    }

    @OneToMany(mappedBy = "role")
    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        users = users;
    }
}

区域

@Entity
@javax.persistence.Table(name = "areas", schema = "public", catalog = "PocketOrder")
public class Area {
    private int id;
    private String name;
    private List<User> users;


    private List<Table> tables;

    @Id
    @Column(name = "id", nullable = false)
    public int getId() {
        return id;
    }

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

    @Basic
    @Column(name = "name", nullable = false, length = 20)
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Area area = (Area) o;

        if (id != area.id) return false;
        if (name != null ? !name.equals(area.name) : area.name != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = id;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        return result;
    }

    @ManyToMany
    @JoinTable(name = "areas_users", catalog = "PocketOrder", schema = "public", joinColumns = @JoinColumn(name = "area_fk", referencedColumnName = "id", nullable = false), inverseJoinColumns = @JoinColumn(name = "user_fk", referencedColumnName = "id", nullable = false))
    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

    @OneToMany(mappedBy = "area")
    public List<Table> getTables() {
        return tables;
    }

    public void setTables(List<Table> tables) {
        this.tables = tables;
    }
}

Answer 1

尝试在特定点使用 @JsonSerialize ：

样本：

1 - 映射您的字段

@JsonSerialize(using = ExampleSampleSerializer.class)
@ManyToOne
private Example example;

2 - 创建自定义jackson序列化程序（这里可以控制序列化）

public class ExampleSampleSerializer extends JsonSerializer<Example> {
    @Override
    public void serialize(Example value, JsonGenerator jsonGenerator, SerializerProvider serializers) throws IOException, JsonProcessingException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeFieldName("first");
        jsonGenerator.writeNumber(value.getFirstValue());
        jsonGenerator.writeFieldName("second");
        jsonGenerator.writeNumber(value.getSecondValue());
        jsonGenerator.writeFieldName("third");
        jsonGenerator.writeNumber(value.getAnyAnotherClass().getThirdValue());
        jsonGenerator.writeEndObject();
    }
}

Answer 2

我处理多对多关系的方法是使用

@JsonIgnore

在一个实体上。例如，我们有Person和Child实体。一个人可以有多个孩子，反之亦然。在Person上，我们有：

public class Person
{
  //Other fields ommited
     @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
     @JoinTable(name = "person_child",
                    joinColumns = {
        @JoinColumn(name = "person_id", referencedColumnName = "id", nullable = false, 
        updatable = false)
         },
                    inverseJoinColumns = {
                @JoinColumn(name = "child_id", referencedColumnName = "id", nullable = 
                false, updatable = false)
        })
private Set<Child> children = new HashSet<>() ;

}

在Child上，我们有：

public class Child
{
      @JsonIgnore
      @ManyToMany(mappedBy = "children", fetch = FetchType.LAZY)
      private Set<Person> people = new HashSet<>() ;
}

现在，当我们获得一个Person时，我们还将获得他所有关联的孩子。但是，当我们得到一个Child时，我们就不会得到所有的People，因为上面有@JsonIgnore批注。这样可以解决“无限递归”问题，并引发此问题。

我的解决方法是编写查询以使所有与特定child_id相连的人。在下面，您可能会看到我的代码：

public interface PersonDAO extends JpaRepository<Person, Long>
{

        @Query(value = "SELECT * " +
        " FROM person p INNER JOIN person_child j " +
        "ON p.id = j.person_id WHERE j.child_id = ?1 ", nativeQuery = true)
         public List<Person> getPeopleViaChildId(long id);
}

每当我想从孩子那里得到所有人时，我都会使用它。

使用Spring Boot，Jackson和Hibernate的多对多关系

更新

用户

的UserRole

区域

2 个答案: