Using DocLister prepare to Build Image Paths from Resource IDs

DocLister is often used to render catalogs where the image path is not stored directly in the resource. Instead, files live in a predictable folder such as /images/{id}/, and the output layer must derive the file path for each item.

The problem

You can access placeholder values inside the item template, but sometimes you need to transform them first and expose a ready-to-use path. That is where prepare becomes useful.

Typical storage rule

/images/123/main.jpg
/images/124/main.jpg

Prepare example

&prepare=`catalogPrepare`

function catalogPrepare($data, $modx, $DL, $e) {
    $id = $data['id'];
    $data['catalog_image'] = "/images/{$id}/main.jpg";
    return $data;
}

Using the prepared field in the template

<img src="[+catalog_image+]" alt="[+pagetitle+]">

Why this is better than hardcoding logic in the chunk

• the chunk stays readable
• the path-building rule stays in one place
• you can add file existence checks or fallback logic later
• the same prepare function can be reused in multiple listings

If your catalog relies on consistent folder naming, prepare is one of the cleanest ways to turn raw resource data into front-end-ready image paths.