JPA, How to find an object that has composite id?

Question

Based on second approach answered here I designed my JPA class.

@Entity(name = "SearchKeywordJPA")
@IdClass(SearchKeywordJPA.SearchKeyId.class)
public class SearchKeywordJPA implements Comparable<SearchKeywordJPA> {

    @Id
    private String keyword;
    @Id
    private long date;
    private String userUUID;

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

        SearchKeywordJPA that = (SearchKeywordJPA) o;

        if (date != that.date) return false;
        if (!keyword.equals(that.keyword)) return false;
        if (!userUUID.equals(that.userUUID)) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = keyword.hashCode();
        result = 31 * result + (int) (date ^ (date >>> 32));
        result = 31 * result + userUUID.hashCode();
        return result;
    }

    @Override
    public String toString() {
        return "SearchKeywordJPA{" +
                "keyword='" + keyword + '\'' +
                ", date=" + date +
                ", userUUID='" + userUUID + '\'' +
                '}';
    }

    public String getKeyword() {
        return keyword;
    }

    public void setKeyword(String keyword) {
        this.keyword = keyword;
    }

    public long getDate() {
        return date;
    }

    public void setDate(long date) {
        this.date = date;
    }

    public String getUserUUID() {
        return userUUID;
    }

    public void setUserUUID(String userUUID) {
        this.userUUID = userUUID;
    }

    @Override
    public int compareTo(SearchKeywordJPA searchRecord) {
        long comparedDate = searchRecord.date;

        if (this.date > comparedDate) {
            return 1;
        } else if (this.date == comparedDate) {
            return 0;
        } else {
            return -1;
        }
    }

    /**********************
     * Key class
     **********************/
    public class SearchKeyId {
        private int id;
        private int version;
    }
}

In my servlet I want to check datastore and store my object if is not exist.

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    ...
            for(SearchKeywordJPA item: applicationList) {
                if(!isRecorded(item))
                    storeRecord(item);
            }

        }

    private boolean isRecorded(SearchKeywordJPA record) {
        EntityManager em = EMF.get().createEntityManager();

        SearchKeywordJPA item = em.find(SearchKeywordJPA.class, record);
        return item != null;

    }

    private void storeRecord(SearchKeywordJPA record) {
        EntityManager em = EMF.get().createEntityManager();

        em.persist(record);
    }

However when I run, application crashes and log says

javax.persistence.PersistenceException: org.datanucleus.store.appengine.FatalNucleusUserException: Received a request to find an object of type com.twitterjaya.model.SearchKeywordJPA identified by SearchKeywordJPA{keyword='airasia', date=1335680686149, userUUID='FFFF0000'}.  This is not a valid representation of a primary key for an instance of com.twitterjaya.model.SearchKeywordJPA.

What is the reason? any suggestion would be appreciated. Thanks

Answer 1

You pass an instance of the IdClass into em.find ... i.e SearchKeyId. Obviously if you really have an IdClass that has no equals/hashCode/toString/constructor then you will likely get many problems. Those problems will only be increased by using an ancient plugin for GAE/Datastore.

Answer 2

If your Key is

@Entity(name = "SearchKeywordJPA")
@IdClass(SearchKeywordJPA.SearchKeyId.class)
public class SearchKeywordJPA implements Comparable<SearchKeywordJPA> {

you are doing it wrong.

1. IdClass does not need any annotation of @IdClass just the @Id annotation.
2. Key can not be an entity.
3. Need to implements Serializable , comparable is not needed
4. Need to override equals and hascode and have no arg constructor

Class key need to be as follows.

public class SearchKeyId implements Serializable {

    private String keyword;

    private long date;

And your entity I assume something like this.

@Entity(name = "SearchKeywordJPA")
@IdClass(SearchKeyId.class)
public class SearchKeywordJPA {
    @Id
    private String keyword;
    @Id
    private long date;

    private String userUUID;

• Just consider that find method will use the SearchKey.class to find the entities.
• Fields that are in the IdClass need to have @Id annotation in the entity.
• Key can not be an entity on its own.
• Comparable is not really needed as all the comparison are placed in the IdClass