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Using a preAdd trigger on a hidden attribute

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ATK Howto: Using a preAdd trigger on a hidden attribute

Complexity: Advanced
Author: Meinaart van Straalen <meinaart@zicht.nl>

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Issue

I wanted to use the news table in my database for 2 sections of the website (backend and frontend). So I added a field called "is_backend" to the table "news".

The most userfriendly solution for editing this table was to create 2 nodes. I called these nodes "news_backend" and "news_site".

Because both the "news_site" and "news_backend" contained the same fields I created a base "news" node containing all the basic fields. The "news_site" and "news_backend" are extending the "news" node. I wanted to add a filter on the "is_backend" field so the right items would show up in the admin-view.

I also wanted to fill the "is_backend" field with either "0" or "1". I tried to use the preAdd functionality for this but it wasn't working the way I expected. That's why I wrote this HowTo to share the solution for this problem.

Code

See the comments in the code for an explanation. 

class news extends atkNode 
{
  function news($type="news",$flags=0) 
  {
    // The $type is important, otherwise the links in the admin
    // view will goto this node instead of to the child node

    $this->atkNode($type, NF_ADD_LINK);
		
    $this->add(new atkAttribute("news_id", AF_AUTOKEY));
    $this->add(new atkAttribute("title", AF_SEARCHABLE));
    $this->add(new atkTextAttribute("text", AF_SEARCHABLE|AF_HIDE_LIST));
		
    // You have to add the is_backend property to the parent node 
    // because otherwise you can't use it in the preAdd function.		
    $this->add(new atkBoolAttribute("is_backend"));

    $this->setTable("news");
  }
}

The "news_backend" is almost the same as the "news_site" node, just replace the 1's with 0's :). 

// Import the parent node, otherwise you can't extend it
// "modules" is the name of the modules directory and 
// "inhoud" the name of the module
atkimport("modules.inhoud.news"); 

class news_backend extends news 
{
  function news_backend() 
  {
    // Call constructor of parent node with the name of the current node
    // so the atkNode function can be called with the right node name
    parent::news("news_backend");	

    // This filter takes care of only showing the items with the is_backend
    // field set to '1'.
    $this->addFilter("is_backend","1");

    // This is basically the trick; hide the is_backend field that is created
    // in the parent node.
    $attr = &$this->getAttribute("is_backend"); 
    $attr->addFlag(AF_HIDE); 
  }
	
  // preAdd function, will only work if the "is_backend" field is present 
  // and visible(!) in the parent node.
  function preAdd(&$record) 
  {
    $record["is_backend"] = 1;
  }
}

Comments

Feel free to correct my English grammar :).

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