CCK is an excellent way of customizing node types without so much as a line of custom PHP. However, if you wish the node to be part of some sort of dynamic process where nodes interact or are part of a process, you'll probably need to delve into widgets and fields a little bit deeper.

In this case, we wanted to link a node describing a petition with node describing a petitioner (name, address, email, etc.)- and we wanted to take advantage of CCK. We have a parent-child relationship, where at least one of the nodes must have a field pointing to it's counterpart. Fortunately, the nodereference field already exists, so all we need to do is supply it with data. We're going to do just that by supplying it with the last argument of the referring URL.

Start you module off by creating a .info file similar to this one:

<?php name = Auto Node Reference description = Supplies a Node ID based on the last argument of the referring URL dependencies = content nodereference package = CCK ?>

The dependencies are important- all CCK modules are dependant on the content module, and the nodereference module defines the field we wish to use.

Next, begin your .module file with hook_widget_info. This defines the label for your widget and the field types that it will work with. If you don't know the machine-readable name of the field, look at the hook_widget_info of a widget that already works with the field.

Next, you can set up custom settings for your widget to allow administrators to modify its behaviour, through hook_widget_settings. In this case, we're not implementing this, but if we were, it might look like this:

The final hook to be written is hook_widget. It is responsible for preparing data for the form, drawing the form, and then preparing the data to be saved by the field. The most crucial part is understanding how the field expects the data to be presented. You'll need to look at the hook_field of the field you're writing for to determine how you will need to manipulate the data. It will look something like this:

In this case, we don't need to massage the data, but if we did, we could do it by handling the 'prepare form values' or 'process form value' cases of $op. The naming of the form elements is crucial, as the data is saved to the $node_field variable accordingly.

Coding a widget is a relatively painless exercise that permits you to customize the CCK interface while writing an absolute minimum of code.