Question

I am clustering tweets based on a search from Twitter and trying to store the results in a database using Hibernate in Java. When I try to save the SearchResults object, I get an error like the following:

org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session

What do I need to do so that both the TweetCluster.java and the SearchResults.java can point to the same table of Tweets in the database? I could change TweetCluster.java so it points to a separate table which stores the tweets again, but that seems like a waste of space.

I’ve pulled out the important code as shown below.

@Entity
@Table(name="search_results")
public class SearchResults {

  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private long searchId;

  @ManyToMany(targetEntity = Tweet.class, cascade=CascadeType.ALL, fetch=FetchType.EAGER)
  @OrderColumn(name="orderIndex")
  private List<Tweet> tweets;

  @OneToMany(targetEntity = TweetCluster.class, cascade=CascadeType.ALL, fetch=FetchType.EAGER, orphanRemoval=true)
  @OrderColumn(name="orderIndex")
  private List<TweetCluster> clusters;

  public SearchResults() {
    tweets = new ArrayList<Tweet>();
    clusters = new ArrayList<TweetCluster>();
  }

  public List<Tweet> getTweets() {
    return tweets;
  }

  public void addTweet(Tweet tweet){
    tweets.add(tweet);
  }


  public void addCluster(TweetCluster cluster){
    clusters.add(cluster);
  }

  public List<TweetCluster> getClusters() {
    return clusters;
  }

}


@Entity
@Table(name="tweet_cluster")
public class TweetCluster {

  @Id
  @GeneratedValue(strategy=GenerationType.IDENTITY)
  private long id;
  private String name;

  @ManyToMany(targetEntity = Tweet.class, fetch=FetchType.EAGER)
  @OrderColumn(name="orderIndex")
  private List<Tweet> tweets;

  public TweetCluster(){
    tweets = new ArrayList<Tweet>();
  }

  public TweetCluster(String name){
    this();
    this.name=name;
  }

  public long getId(){
     return id;
  }

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

  public List<Tweet> getTweets() {
    return tweets;
  }

  public void addTweet(Tweet tweet){
    tweets.add(tweet);
  }

}


@Entity
@Table(name="tweet")
public class Tweet {

  @Id
  @GenericGenerator(name="assigned", strategy = "assigned")
  private long tweetId;

  private String text;

  public Tweet(){

  }

  public long getTweetId() {
    return tweetId;
  }

  public void setTweetId(long id){
    this.tweetId = id;
  }

  public String getText() {
    return text;
  }

  public void setText(String text) {
    this.text = text;
  }

}

EDIT:

To save the results, I run code something like the following:

SearchResults searchResult = new SearchResults();
searchResult .addCluster(new TweetCluster("cluster1"));
searchResult .addCluster(new TweetCluster("cluster2"));

searchResult.addTweet(new Tweet("Tweet 1"));
searchResult.addTweet(new Tweet("Tweet 2"));
searchResult.addTweet(new Tweet("Tweet 3"));
session.saveOrUpdate(searchResult);

The exception gets thrown at saveOrUpdate

Answer 1

It turns out the problem was really simple. The generator for Tweet is assigned. In my unit test I forgot to assign an id. Thus several tweets had an id of zero.