How can I get the selected value in the multiselect dropdown?

Question

I have a three table in my database, article category and art_cat

article has the id,name,status of the article

category has id,name,status of the category

art_cat has id,art_id and cat_id in the tables.

I have the values inserted respectively, but in my "article form" my category values are not coming selected. I have a multi select dropdown for the category. I have a distinct form for "category". that means my "article form" data goes in article table and "category form" data goes in art_cat table.

$fieldset->addField('category_id', 'multiselect', array(
 'label' => 'Category',
 'name' => 'category_id[]',
 'values' => Mage::helper('blog')->getCategoryOptionValues(true),
 'disabled' => false,
 'index' => 'category_id',
 ));

and here is my helper file Data.php

static function getCategoryOptionValues($inlcudeNone = false) {
 $collection = Mage::getModel('blog/blog')->getCollection();
 $values = array();
 if ($inlcudeNone){
 $values[] = array('label' => "--None--", 'value' => 0);
 }
 foreach ($collection as $category) {
 $values[] = array('label' => $category->getName(), 'value' => $category->getId());
 }
 return $values;
 }

How can I get the selected value for the category multi select dropdown. Please somebody help me with this.

Answer 1

During the addField call you can specify the option value. For normal field types this takes a string and will set this as the field value, but for multiple select fields you can specify a comma separated string containing each selected value.