在Hibernate中使用外键将对象与另一个表中的数据映射

Question

I am trying to populate the data within this class from a database using Hibernate and javax persistence annotations. Here are the relevant database structures.

table Poss_resp     
ID  qst_id  resp_text
int int text

table Responses         
ID  qst_id  usr_id  resp_id
int int int int

I am trying to populate the Response class shown below with Responses.ID, and Poss_resp.resp_text. Poss_resp holds possible answers to a question. Responses holds the actual answers given. resp_id is a foreign key for Poss_resp. However, I just want the resp_text string stored, I do not want a whole new object. Is there some way to achieve this? I cannot figure out how to tell Hibernate how to use something other than Response's primary key, nor have I determined the proper JOIN syntax.

My Response class:

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

    private long id;
    private long qst_id;
    private long resp_id;
    private String resp_text;


    /**
     * 
     */
    public Response() {
        // TODO Auto-generated constructor stub
    }


    /**
     * @return the id
     */
    @Id
    @Generated(value="assigned")
    @Column(name="ID")
    public long getId() {
        return id;
    }


    /**
     * @param id the id to set
     */
    public void setId(long id) {
        this.id = id;
    }


    /**
     * @return the qst_id
     */
    @Column(name="qst_id")
    public long getQst_id() {
        return qst_id;
    }


    /**
     * @param qst_id the qst_id to set
     */
    public void setQst_id(long qst_id) {
        this.qst_id = qst_id;
    }


    /**
     * @return the resp_id
     */
    @Column(name="resp_id")
    public long getResp_id() {
        return resp_id;
    }


    /**
     * @param resp_id the resp_id to set
     */
    public void setResp_id(long resp_id) {
        this.resp_id = resp_id;
    }


    /**
     * @return the resp_text
     */
    public String getResp_text() {
        return resp_text;
    }


    /**
     * @param resp_text the resp_text to set
     */
    public void setResp_text(String resp_text) {
        this.resp_text = resp_text;
    }

If at all possible, I would prefer annotations.

Answer 1

The relationship of Responses and Poss_resp table is many-to-one , you should map this relationship in the Response class . Otherwise , hibernate has not enough knowledge to get Poss_resp.resp_text given the Responses.resp_id

Your Poss_resp table should be mapped to an an entity class (say Class PossResp )

Then , you can declare many-to-one relationship using the @ManyToOne and @JoinColumn , like this:

@Entity
@Table(name="responses")
public class Response {
   ..................
   private PossResp possResp;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "resp_id") 
    public PossResp getPossResp() {
        return possResp;
    }
    ................

}

To get the resp_text given an Response object , call

 response.getPossResp().getRespText();

---

I do not want a whole new object. Is there some way to achieve this?

If you only map the long resp_id instead of the PossResp object in PossResp entity , I am afraid that you have to manually write the HQL/SQL/Criteria to get the resp_text using the long resp_id and then set it back to the Response via the setResp_text() setter . But in this way, you definitely cannot enjoy the benefits provided by hibernate IMO.