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single valued field + join

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nirro

Post subject: single valued field + join

Posted: Tue Nov 02, 2010 6:35 pm

Newbie

Joined: Tue Nov 02, 2010 6:22 pm
Posts: 3

Hello,

I'm trying to execute a simple HQL query with JOIN:

Code:

SELECT title FROM Post p JOIN p.title title

where the Post entity is:

Code:

@Entity
public class Post
{
    private long id;
    private String title;

    public Post()
    {
    }

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public long getId()
    {
        return id;
    }

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

    @Column
    public String getTitle()
    {
        return title;
    }

    public void setTitle(String title)
    {
        this.title = title;
    }
}

But I got an exception:

Quote:

java.lang.NullPointerException
at org.hibernate.hql.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:391)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3671)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3452)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:3325)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:733)

Is it possible to create JOIN for a single valued property or this feature is unsupported? I use Hibernate 3.6.0. Thanks.

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nordborg

Post subject: Re: single valued field + join

Posted: Wed Nov 03, 2010 2:54 am

Expert

Joined: Wed Mar 03, 2004 6:35 am
Posts: 1240
Location: Lund, Sweden

Joining only works for related entities. You could do like this:

Code:

SELECT p.title FROM Post p

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nirro

Post subject: Re: single valued field + join

Posted: Wed Nov 03, 2010 4:05 am

Newbie

Joined: Tue Nov 02, 2010 6:22 pm
Posts: 3

nordborg wrote:

Joining only works for related entities. You could do like this:

Code:

SELECT p.title FROM Post p

nordborg, thanks for your answer! Actually, "SELECT p.title FROM Post p" works fine. It is one of possible solutions.

But I still have a question: is query "SELECT title FROM Post p JOIN p.title title" syntactically incorrect?

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nordborg

Post subject: Re: single valued field + join

Posted: Wed Nov 03, 2010 4:42 am

Expert

Joined: Wed Mar 03, 2004 6:35 am
Posts: 1240
Location: Lund, Sweden

The syntax is correct, but it will only work if 'title' is another entity, not if it is a property.

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nirro

Post subject: Re: single valued field + join

Posted: Wed Nov 03, 2010 4:52 am

Newbie

Joined: Tue Nov 02, 2010 6:22 pm
Posts: 3

nordborg wrote:

The syntax is correct, but it will only work if 'title' is another entity, not if it is a property.

I get it! Thanks!

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