How to query JDO persistent objects in unowned relationship model?

Question

Hello,

I'm trying to migrate my app from PHP and RDBMS (MySQL) to Google App Engine and have a hard time figuring out data model and relationships in JDO. In my current app I use a lot of JOIN queries like:

SELECT users.name, comments.comment
FROM users, comments
WHERE users.user_id = comments.user_id
AND users.email = '[email protected]'

As I understand, JOIN queries are not supported in this way so the only(?) way to store data is using unowned relationships and "foreign" keys. There is a documentation regarding that, but no useful examples. So far I have something like this:

@PersistenceCapable
public class Users {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    private String name;
    
    @Persistent
    private String email;
    
    @Persistent
    private Set<Key> commentKeys;

    // Accessors...
}

@PersistenceCapable
public class Comments {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    @Persistent
    private String comment;
    
    @Persistent
    private Date commentDate;

    @Persistent
    private Key userKey;

    // Accessors...
}

So, how do I get a list with commenter's name, comment and date in one query? I see how I probably could get away with 3 queries but that seems wrong and would create unnecessary overhead. Please, help me out with some code examples.

-- Paul.

Answer 1

Can only comment on what is valid JDOQL for that

SELECT this.name, commentVar.comment FROM mydomain.Users WHERE this.key == commentVar.userKey && this.email = '[email protected]' VARIABLES mydomain.Comments commentVar

whether GAE/J deems to implement it is for Google to answer.