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 Post subject: How to query a many-to-many association with Hibernate
PostPosted: Tue Jan 31, 2017 4:14 am 
Newbie

Joined: Tue Jan 31, 2017 4:07 am
Posts: 4
Hi all,
I have following 3 tables in mysql db
[img]

mysql> select * from person;
+---------+--------+-----------------+-----------------+---------------------+----------+
| user_id | active | email | fullName | joined | password |
+---------+--------+-----------------+-----------------+---------------------+----------+
| bucky | 1 | bucky@abc.com | Bucky Wall | 2017-01-30 12:43:46 | bucky |
| james | 1 | james@abc.com | James Goedic | 2017-01-30 12:43:19 | james |
| praveen | 1 | praveen@abc.com | Praveen Reddy S | 2017-01-30 12:37:40 | praveen |
| priya | 1 | priya@abc.com | Priya Reddy | 2017-01-10 10:30:17 | priya |
+---------+--------+-----------------+-----------------+---------------------+----------+
4 rows in set (0.00 sec)

mysql> select * from tweet;
+----------+---------------------+----------------------------+---------+
| tweet_id | created | message | user_id |
+----------+---------------------+----------------------------+---------+
| 1 | 2017-01-30 12:45:37 | @Bucky!. Meet me in office | james |
| 2 | 2017-01-30 12:45:58 | @James!. How nare you? | praveen |
| 3 | 2017-01-30 12:46:10 | Hi, Every One | praveen |
| 4 | 2017-01-30 12:46:38 | @James: Hellow James | bucky |
| 5 | 2017-01-31 10:30:50 | This is Priya | priya |
+----------+---------------------+----------------------------+---------+
5 rows in set (0.00 sec)

mysql> select * from following;
+---------+--------------+
| user_id | following_id |
+---------+--------------+
| praveen | bucky |
| praveen | james |
+---------+--------------+
2 rows in set (0.00 sec)
[/img]

My Two Entity classes are

Person.java
Code:
@Entity
public class Person {

   @Id
   @Column(name = "user_id")
   private String userId;
   private String password;
   private String email;
   private String fullName;

   @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
   @JoinTable(name = "following", joinColumns = { @JoinColumn(name = "user_id") },
   inverseJoinColumns = { @JoinColumn(name = "following_id") })
   private List<Person> following = new ArrayList<Person>();


Tweet.java

Code:
@Entity
public class Tweet {

   @Id
   @GeneratedValue(strategy=GenerationType.AUTO)
   @Column(name="tweet_id")
   private int tweetId;
   private String message;
   private Date created;

   @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
   @JoinColumn(name="user_id")
   private Person person;


Now I want to display messages of user praveen, and also all the messages mapped to praveen user in the following table. That means praveen user have 2 messages and his following users have 2 messages . Total 4 messages should be displayed. I really don't know how to retrieve this info using any technique in Hibernate. Please help me


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 Post subject: Re: Hibernate ManyToMany HQL issue
PostPosted: Tue Jan 31, 2017 5:01 am 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1628
Location: Romania
A native SQL query is like a Magic Wand. You only need HQL for fetching entities that you plan to modify.

Back to your problem, use this native query:

Code:
select *
from tweets t
where
    t.user_id = 1 or
    t.user_id in (
        select f.following_id from following f where f.user_id = 1
    )


You can also map it to an entity, as explained in the aforementioned article.


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 Post subject: Re: How to query a many-to-many association with Hibernate
PostPosted: Tue Jan 31, 2017 5:48 am 
Newbie

Joined: Tue Jan 31, 2017 4:07 am
Posts: 4
Using native SQL i got the output. But my requirement is not use native sql. Please help


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 Post subject: Re: How to query a many-to-many association with Hibernate
PostPosted: Tue Jan 31, 2017 5:59 am 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1628
Location: Romania
The query is just the same with HQL or JPQL:

Code:
select t
from Tweets t
join User t.person u
where
    u.id = 1 or
    u.id in (
        select f_f.id
        from Following f
        join f.user f_u
        join f.following f_f
        where f_u.id = 1
    )


This query assumes that the Following entity has 2 @ManyToOne associations:

Code:
@ManyToOne
private Person user;

@ManyToOne
private Person following;


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 Post subject: Re: How to query a many-to-many association with Hibernate
PostPosted: Tue Jan 31, 2017 6:00 am 
Newbie

Joined: Tue Jan 31, 2017 4:07 am
Posts: 4
Folowing is my native code. Its working good. But i need HQL

Code:
[b]select * from tweet t where t.user_id =(select following_id from following where following_id=t.user_id) or t.user_id='praveen';[/b]


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 Post subject: Re: How to query a many-to-many association with Hibernate
PostPosted: Tue Jan 31, 2017 6:04 am 
Newbie

Joined: Tue Jan 31, 2017 4:07 am
Posts: 4
Thanks for the reply. But that query works only for tweetid 1. But i need all tweets whose user name is some thing. So I wanted to list all tweet messages of a user and his following users tweet messages .


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 Post subject: Re: How to query a many-to-many association with Hibernate
PostPosted: Tue Jan 31, 2017 6:32 am 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1628
Location: Romania
If you read the HQL and JPQL User Guide chapter, you'll find the answer for such a trivial question of how to use a named parameter in an entity query.


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