Filling fields forms in backend from two different tables

Question

Currently, we have several forms that allow to edit/delete information, each one loading the data from one particular table. But what I want is to be able to load on the Form.php information from different tables.

On the code below there is a field name imagefilename. This field belongs to another table that is linked with a foreign key to the one I'm loading on the first if sentence on the line $data = Mage:: registry('banners_data')->getdata(); that was saved on the previous page at user click.

So I have the main ID and can search on the images table the needed data. But no matter how I try, it does not correctly load the information I need. I tried searching for samples but no luck or maybe I'm just not using the correct terms.

Here is a part of my _prepareForm function, without any code to load the image table as it was triggering some errors.

    protected function _prepareForm() {
        if (Mage::registry('banners_data')->getdata())  {
            $data = Mage::registry('banners_data')->getdata();
        }
        elseif (Mage::getSingleton('adminhtml/session')) {
            $data = Mage::getSingleton('adminhtml/session')->getdata();
            Mage::getSingleton('adminhtml/session')->getdata(null);
        }
        else {
            $data = array();
        }

        $form = new Varien_Data_Form(
            array('id' => 'edit_form',
                    'action' => $this->getUrl('*/*/save', $params),
                    'method' => 'post',
                    'enctype' => 'multipart/form-data',
    ));

        $fieldset = $form->addFieldset('banners_form', 
            array('legend' =>Mage::helper('banners')->__('Campaign details page')));

        $fieldset->addField('banner_name', 'text',
            array(  'label'     => Mage::helper('banners')->__('Name'),
                    'class'     => 'required-entry',
                    'required'  => true,
                    'name'      => 'banner_name',
                    'note'      => Mage::helper('banners')->__('campaign name'),
                    'tabindex' => 1
    ));
.....
        $fieldset->addField('imagefilename', 'file',
            array(  'label'   => Mage::helper('banners')->__('Image to upload'),
                    'name'    => 'imagefilename',
                    'disabled'=> false,
                    'note'    => Mage::helper('banners')->__('Image you want to upload'),
                    'readonly'=> true,
                    'tabindex'=> 10
.....
}

Answer 1

If you are certain, that you have imagefilename ID in $data, then load image file name from DB, and add it to $data with 'imagefilename' then when you do setValues, it should be picked up. If it is not too much overhead, add a JOIN to initial data loading part and fetch image file name there. Will save you one more trip to database.