Preserve many-to-one mapping in mapped objects as well

[shaan7]

In my usecase, multiple Media (songs) can have the same Artist, hence a many to one relationship defined like this-

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template <> void register_class(QxClass<Artist> & a)
{
    a.id(& Artist::m_name, "name");

    a.relationOneToMany(& Artist::m_media, "media", "artist_id");
}

The relation works as I can see from the database. However, when I am trying to load the media, even though they are related to the same Artist the two Artist objects are different (even though the names are same).
Consider this test-

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void test()
{
    qx::dao::create_table<Album>();
    qx::dao::create_table<Artist>();
    qx::dao::create_table<Media>();

    QSharedPointer<Artist> artist(new Artist("Shaan"));

    QSharedPointer<Media> media1(new Media("uri://media1"));
    QSharedPointer<Media> media2(new Media("uri://media2"));

    media1->setArtist(artist);
    media2->setArtist(artist);

    qx::dao::insert(media1);
    qx::dao::insert(media2);

    QSharedPointer<Media> fetchedMedia1(new Media("uri://media1"));
    QSharedPointer<Media> fetchedMedia2(new Media("uri://media2"));

    typedef qx::QxCollection< QString, QSharedPointer<Media> > MediaList;
    MediaList medias;
    qx::dao::fetch_all_with_all_relation(medias);

    _foreach (QSharedPointer<Media> media, medias) {
        qDebug() << media->artist().data() << media->artist()->name();
    }
}

This outputs-

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0x2357f80 "Shaan"
0x23513b0 "Shaan"

Is there a way I can ask QxOrm that the two Media to point to the same object of Artist in this case? I'd want the output of the above program to be this-

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0x2357f80 "Shaan"
0x2357f80 "Shaan"

[qxorm]

Hello,

Is there a way I can ask QxOrm that the two Media to point to the same object of Artist in this case?

No, even if the fetched items is the same object in database, QxOrm library will create a new instance.

But you can easily manage it yourself using QxCache module !
More details about qx::cache here :
- http://www.qxorm.com/qxorm_en/faq.html#faq_220
- http://www.qxorm.com/doxygen/html/group___qx_cache.html

[honrel]

Hello,

Is there a way I can ask QxOrm that the two Media to point to the same object of Artist in this case?

No, even if the fetched items is the same object in database, QxOrm library will create a new instance.

But you can easily manage it yourself using QxCache module !
More details about qx::cache here :
- http://www.qxorm.com/qxorm_en/faq.html#faq_220
- http://www.qxorm.com/doxygen/html/group___qx_cache.html

Hello, I have а similar problem?
I need to implement stateful session.
Great solution is to use RAII such as odb orm (http://www.codesynthesis.com/products/o ... xhtml#11.1).

Code: Select all

void test()
{
    qx::dao::create_table<Album>();
    qx::dao::create_table<Artist>();
    qx::dao::create_table<Media>();

    {
        QSharedPointer<Artist> artist(new Artist("Shaan"));

        QSharedPointer<Media> media1(new Media("uri://media1"));
        QSharedPointer<Media> media2(new Media("uri://media2"));

        media1->setArtist(artist);
        media2->setArtist(artist);

        qx::dao::insert(media1);
        qx::dao::insert(media2);

        QSharedPointer<Media> fetchedMedia1(new Media("uri://media1"));
        QSharedPointer<Media> fetchedMedia2(new Media("uri://media2"));

        qx::dao::fetch_by_id_with_all_relation(fetchedMedia1);
        qx::dao::fetch_by_id_with_all_relation(fetchedMedia1);

        qAssert(media1 == fetchedMedia1);
        qAssert(media2 == fetchedMedia2);
        qAssert(fetchedMedia1->artist() == artist);
        qAssert(fetchedMedia1->artist()->media() == fetchedMedia1);
    }
}


Is it possible? Please help me!

[qxorm]

Hello,

Is it possible?

QxOrm library will create new instances each time you fetch something.

If you want to keep something in memory, and then check later if the instance exist or not, you have to use the QxCache module.
More details here :
- http://www.qxorm.com/qxorm_en/faq.html#faq_220
- http://www.qxorm.com/doxygen/html/group___qx_cache.html