Best way to add classes to bean?

Do you want to add classes to the bean (in the block content) or the parent block itself?

If the former, you can use template_preprocess_bean(&$variables) and if the latter you can use template_preprocess_block(&$variables) and add classes to the $variables['classes_array'].

See this page for info about preprocess functions: http://drupal.org/node/223430

For example (in your theme's template.php file):

This example adds a custom class to the bean:

<?php
/**
 * Override or insert variables into the bean templates.
 */
function YOURTHEME_preprocess_bean(&$variables) {
  // Add a custom class to the bean entity.
  $variables['classes_array'][] = 'my-custom-class';
}
?>

This example adds a class to the parent block that contains the bean type and also adds a template suggestion based on the bean type:

<?php
/**
 * Override or insert variables into the block templates.
 */
function YOURTHEME_preprocess_block(&$variables) {
  // For bean blocks.
  if ($variables['block']->module == 'bean') {
    // Get the bean elements.
    $beans = $variables['elements']['bean'];
    // There is only 1 bean per block.
    $bean = $beans[reset(element_children($beans))];
    // Add bean type classes to the parent block.
    $variables['classes_array'][] = drupal_html_class('block-bean-' . $bean['#bundle']);
    // Add template suggestions for bean types.
    $variables['theme_hook_suggestions'][] = 'block__bean__' . $bean['#bundle'];
  }
}
?>

Actually it seems that for some reason template_preprocess_bean() does not work.

Instead of template_preprocess_bean() you could do this:

<?php
function YOURTHEME_process_entity(&$variables) {
  if ($variables['entity_type'] == 'bean') {
    if ($variables['bean']->type == 'YOUR_BEAN_TYPE') {
      $variables['classes_array'][] = 'your-custom-class';
    }
  }
}
?>

Also, for more themeing chat see #1361756: More theme candidates.

Marking fixed, if you still require more help feel free to reopen.

rooby's suggestion above got me on the right track. However, I couldn't get my modified classes_array to output to the page with hook_process_entity. I had to use the following, which came from the suggestion #1361756: More theme candidates:

<?php
function YOURTHEME_preprocess_block(&$variables) {
  if ($variables['block']->module == 'bean') {
      $variables['classes_array'][] = 'your-custom-class';
  }
}
?>

template_process_entity did not work for me either but template_PREprocess_entity did work and actually helped me add my class where I needed it to be. Because when rendering my entity through views, adding the class via template_preprocess_block does not work.

We include class field(select list) in our beans.
Then use this code to add the class to the entity attributes:

/**
* Runs a entity specific preprocess function, if it exists.
*/
function bean_library_preprocess_entity(&$variables, $hook) {
$function = __FUNCTION__ . '_' . $variables['entity_type'];
if (function_exists($function)) {
$function($variables, $hook);
}
}

/**
* Implementation of template_preprocess_entity().
*/
function bean_library_preprocess_entity_bean(&$variables, $hook) {
if(isset($variables['elements']['#entity']->field_html_bean_class)) {
$newclass = $variables['elements']['#entity']->field_html_bean_class['und'][0]['value'];
$variables['classes_array'][] = $newclass;
}
}
Note that you should change the name of your function to your module name (as usual).

I am new to preprocess functions and curious to know how to insert a token as a class.

Following through with the suggestion at #5. How to insert the block ID (or bean ID) as a class instead of 'your-custom-class' as stated in the examples above.

I think an appropriate token may be [bean:uid]

Temporarily re-opening to aid visability