How to set MINIMUM number of required fields?

Question

I need to set the minimum number of required values for several file fields in Drupal 7. I can only find options to make the field required or set a maximum number of allowed values. Is there any way to set the MINIMUM number of required values?

Answer 1

You can use the Field validation module, and set up a validation rule using "number of selections".
The Field validation module has many validation rules you can set for any of your fields. It works by defining a set of validation rules at first, then you can assign that set to a field.

To answer your question, the validation rule you need to use is the "number of selections". You can define a minimum and a maximum number of values required. Just leave blank the "Maximum number of selections" parameter and set "Minimum number of selections" to your needs.

Answer 2

I found the field validation option resulted in a lot of form submission failure messages, the best was trying to add another field when I had only one complained that I did not have btwn 3 and 5, but did not give me another field.

My solution using hook_form_alter(): Not the most elegant code now that I look at it...

function MYMODULE_form_alter(&$form, &$form_state, $form_id) {

  /**
  * Make sure that there are at least 3 and at most 5 items
  */
  if ($form_id == 'content_type_container_node_form') {

    // Count how many items we have
    $item_count = 0;
    foreach ($form['field_name_items'][ LANGUAGE_NONE ] as $delta => $item) {
      if (is_integer($delta)) {
        $item_count++;
      }
    }

    // If it is a new node then make sure we start with 3 items
    if ($form['nid']['#value'] == NULL && $item_count < 3) {
      $item_template = $form['field_name_items'][ LANGUAGE_NONE ][0];

      // We are adding two items to the one we already have
      for ($i = 1; $i < 3; $i++) {
        $form['field_name_items'][ LANGUAGE_NONE ][ $i ] = $item_template;
        $form['field_name_items'][ LANGUAGE_NONE ][ $i ]['remove_button']['#delta'] = $i;
      }
    }

    // Re-Count how many items we have
    $item_count = 0;
    foreach ($form['field_name_items'][ LANGUAGE_NONE ] as $delta => $item) {
      if (is_integer($delta)) {
        $item_count++;
        // Remove the 'Remove' link for the first 3 items
        if ($item_count <= 3) {
          unset($form['field_name_items'][ LANGUAGE_NONE ][ $delta ]['remove_button']);
        }

      }
    }

    if ($item_count == 5) {
      // Remove add more link if there are 5 items
      unset($form['field_name_items'][ LANGUAGE_NONE ]['add_more']);
    }
  }
}