java - 如何在 Spring Boot 中为只有外键的表映射/创建实体类

Question

我的数据库 (Postgres) 中有以下表格:questions、responses 和 question_response。问题表和响应表之间存在多对多关系，我已经为这两种关系创建了实体类。我现在必须为没有任何主键的 question_respone 表创建一个实体映射。

我读过有关使用 @IdClass 或 @EmbeddedId 的内容，但是，我不确定如何映射两个外键，这两个外键是两个不同类中的主键这些注释。

注意事项:

在实现评论中提到的更改后更新实体

谢谢!

问题.sql

CREATE TABLE questions( 
    id BIGSERIAL PRIMARY KEY,
    question VARCHAR(255)
);

响应.sql

CREATE TABLE responses( 
    id BIGSERIAL PRIMARY KEY,
    response VARCHAR(255)
);

question_respone.sql #

CREATE TABLE question_response(
    question_id bigint REFERENCES questions ON DELETE CASCADE,
    response_id bigint REFERENCES responses ON DELETE CASCADE,
    PRIMARY KEY ( question_id, response_id)
);

问题.java

@Entity
@Table(name = "questions")
public class Question{


    @Id
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="qid_seq")
    @SequenceGenerator(name = "qid_seq", sequenceName="questions_id_seq")
    @Column(name = "id")
    private Long id;


    @Column(name = "questionText")
    private String questionText;

    @OneToMany(mappedBy = "question", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<QuestionResponse> responses;

    public Question() {}

    public Question(String questionText) {
        super();
        this.questionText = questionText;
    }

    public Long getId() {
        return id;
    }

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

    public String getQuestionText() {
        return questionText;
    }

    public void setQuestionText(String questionText) {
        this.questionText = questionText;
    }

    public List<QuestionResponse> getResponses() {
        return responses;
    }
}

问题响应.java

@Entity
@Table(name = "question_response")
public class QuestionResponse {

    @Id
    @ManyToOne 
    private Question question;

    @Id
    @ManyToOne 
    private Response response;



    public QuestionResponse() {
        super();
    }

    public QuestionResponse(Question question, Response response) {
        super();
        this.question= question;
        this.response = response;
    }

    public Question getQuestion() {
        return question;
    }

    public void setQuestion(Question question) {
        this.question = question;
    }

    public Response getResponse() {
        return response;
    }

    public void setResponse(Response response) {
        this.response = response;
    }

}

响应.java

@Entity
@Table(name = "responses")
public class Response {

    @Id
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="rid_seq")
    @SequenceGenerator(name = "rid_seq", sequenceName="questions_id_seq")
    @Column(name = "id")
    private Long id;

    @Column(name = "responseText")
    private String responseText;

    @OneToMany(mappedBy = "response", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<QuestionResponse> question;

    public Response() {}

    public Response(String responseText) {
        super();
        this.responseText = responseText;
    }

    public Long getId() {
        return id;
    }

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

    public String getResponseText() {
        return responseText;
    }

    public void setResponseText(String responseText) {
        this.responseText = responseText;
    }

    public List<QuestionResponse> getQuestion() {
        return question;
    }

}

# WildFly 控制台#

13:54:49,581 ERROR [org.springframework.boot.SpringApplication] (ServerService Thread Pool -- 86) Application run failed: org.springframework.beans.factory.BeanCreationException:
 Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]:
 Invocation of init method failed; nested exception is org.hibernate.AnnotationException:
 No identifier specified for entity: com.poc.questionnarie.QuestionResponse

Answer 1

您可以按照此处所述将多对多关系分解为一对多对一结构:

https://docs.jboss.org/hibernate/orm/5.2/userguide/html_single/Hibernate_User_Guide.html#associations-many-to-many-bidirectional-with-link-entity