How to join two collections in magento?

Question

Hi I have a castom module news. When I create news I save all my informations in table news. But I need to save author input to table Authors.

And display all informations here

This is my News Grid!!! Please Help Me

class Task_News_Block_Adminhtml_News_Grid extends Mage_Adminhtml_Block_Widget_Grid
{


    protected function _prepareCollection()
    {
        $collection = Mage::getModel('tasknews/news')->getCollection();
        $newsAuthorsTable = Mage::getSingleton('core/resource')->getTableName('tasknews/news');

        $collection->getSelect()->join(array('authors'=> $newsAuthorsTable),
           'main_table.news_id=authors.news_id',
           array());
        $this->setCollection($collection);
        return parent::_prepareCollection();
    }

    protected function _prepareColumns()
    {

        $helper = Mage::helper('tasknews');

        $this->addColumn('news_id', array(
            'header' => $helper->__('News ID'),
            'index' => 'news_id'
        ));

        $this->addColumn('title', array(
            'header' => $helper->__('Title'),
            'index' => 'title',
            'type' => 'text',
        ));

    $this->addColumn('author', array(
            'header' => $helper->__('Author'),
            'index' => 'author',
            'type' => 'text',
        ));


        $this->addColumn('created', array(
            'header' => $helper->__('Created'),
            'index' => 'created',
            'type' => 'date',
        ));

        return parent::_prepareColumns();
    }

 protected function _prepareMassaction()
    {
        $this->setMassactionIdField('news_id');
        $this->getMassactionBlock()->setFormFieldName('news');

        $this->getMassactionBlock()->addItem('delete', array(
            'label' => $this->__('Delete'),
            'url' => $this->getUrl('*/*/massDelete'),
        ));
        return $this;
    }

    public function getRowUrl($model)
    {
        return $this->getUrl('*/*/edit', array(
                    'id' => $model->getId(),
                ));
    }

Answer 1

You are so close you'll kick yourself. There needs to be one change to join()

protected function _prepareCollection()
{
    $collection = Mage::getModel('tasknews/news')->getCollection();
    $newsAuthorsTable = Mage::getSingleton('core/resource')->getTableName('tasknews/news');

    $collection->getSelect()->join(array('authors'=> $newsAuthorsTable),
       'main_table.news_id=authors.news_id',
// must also specify which columns to join
       array('author'));
    $this->setCollection($collection);
    return parent::_prepareCollection();
}

---

Although the above works great it could be neater since it's bad practice to have "model" logic in "block" classes. In the news collection class add:

public function joinAuthors()
{
    $this->join(
        array('authors' => 'tasknews/news'),
        'main_table.news_id=authors.news_id',
        array('author')
    );
    return $this;
}

And now the collection is much easier to use.

protected function _prepareCollection()
{
    $collection = Mage::getModel('tasknews/news')->getCollection()->joinAuthors();
    $this->setCollection($collection);
    return parent::_prepareCollection();
}

---

To save the news and author at the same time I would do this; In the news model add:

protected function _afterSave()
{
    parent::_afterSave();

    if ($this->dataHasChangedFor('author')) {
        Mage::getModel('tasknews/author')
            ->load($this->getId(), 'news_id')
            ->setNewsId($this->getId()) // in case there wasn't a record before
            ->setAuthor($this->getAuthor())
            ->save();
    }

    return $this;
}

// necessary to fill orig data for dataHasChangedFor() to work above
// only called when loading a single object, for collections use joinAuthors()
protected function _afterLoad()
{
    $author = Mage::getModel('tasknews/author')
            ->load($this->getId(), 'news_id')
            ->getAuthor();
    $this->setData('author', $author); // not setAuthor() in case that's a real method
    $this->setOrigData('author', $author); // this value is compared when saving

    return parent::_afterLoad();
}