changing cardinality of form field programmatically

Normally you set the number of fields to show when creating the content type definition. This can either be achieved through the UI or programmatically in the case that you are defining the content type within a module.

The following is the content of a module install file ("namecards_namecard.install") showing how to set cardinality. A value of "-1" represents unlimited. Use a positive value to set a specific number of fields. This is used as part of defining the content type within a module.

Hope this helps.

/**
* Implements hook_install().
*/
function namecards_namecard_install() {
  node_types_rebuild();
  $types = node_type_get_types();

  // Create all the fields we are adding to our content type.
  foreach (_namecards_namecard_installed_fields() as $field) {
    field_create_field($field);
  }

  // Create all the instances for our fields.
  foreach (_namecards_namecard_installed_instances() as $instance) {
    $instance['entity_type'] = 'node';
    $instance['bundle'] = 'namecards_namecard';
    field_create_instance($instance);
  }
}

/**
* Return a structured array defining the fields created by this content type.
*/
function _namecards_namecard_installed_fields() {
  $t = get_t();
  return array(
    'namecards_namecard_phone' => array(
      'field_name' => 'namecards_namecard_phone',
      'label' => $t('Phone'),
      'type' => 'text',
      'cardinality' => -1,
    ),
    'namecards_namecard_fax' => array(
      'field_name' => 'namecards_namecard_fax',
      'label' => $t('Fax'),
      'type' => 'text',
      'cardinality' => -1,
    ),
  );

}

/**
* Return a structured array defining the field instances associated with this content type.
*/
function _namecards_namecard_installed_instances() {
  $t = get_t();
  return array(
    'namecards_namecard_phone' => array(
      'field_name' => 'namecards_namecard_phone',
      'type' => 'text',
      'label' => $t('Phone'),
        'widget' => array(
          'type' => 'text_textfield',
        ),
      'display' => array(
        'example_node_list' => array(
          'label' => $t('Phone'),
          'type' => 'text',
        ),
      ),
      'description' => $t('Phone number format must include country and area codes.  The correct format is: <b>+86 (10) 64460982</b>. Extensions should be separated from the main phone number with a hyphen (e.g. +86 (10) 64460982<b>-123</b>).'),
    ),
    'namecards_namecard_fax' => array(
      'field_name' => 'namecards_namecard_fax',
      'type' => 'text',
      'label' => $t('Fax'),
        'widget' => array(
          'type' => 'text_textfield',
        ),
      'display' => array(
        'example_node_list' => array(
          'label' => $t('Fax'),
          'type' => 'text',
        ),
      ),
      'description' => $t('Fax number format must include country and area codes.  The correct format is: <b>+86 (10) 64220282</b>. Extensions should be separated from the main phone number with a hyphen (e.g. +86 (10) 64220282<b>-123</b>).'),
    ),
  );
}

/**
* Implements hook_uninstall().
*/
function namecards_namecard_uninstall() {
  // Gather all the example content that might have been created while this
  // module was enabled.
  $sql = 'SELECT nid FROM {node} n WHERE n.type = :type';
  $result = db_query($sql, array(':type' => 'namecards_namecard'));
  $nids = array();
  foreach ($result as $row) {
    $nids[] = $row->nid;
  }
  // Delete all the nodes at once
  node_delete_multiple($nids);
  // Loop over each of the fields defined by this module and delete
  // all instances of the field, their data, and the field itself.
  foreach (array_keys(_namecards_namecard_installed_fields()) as $field) {
    field_delete_field($field);
  }
  // Loop over any remaining field instances attached to the namecards_namecard
  // content type (such as the body field) and delete them individually.
  $instances = field_info_instances('node', 'namecards_namecard');
  foreach ($instances as $instance_name => $instance) {
    field_delete_instance($instance);
  }
  // Delete our content type
  node_type_delete('namecards_namecard');
  // Purge all field infromation
  field_purge_batch(1000);
}

Hi,
Your statement:

but how can I display 7 fields on the node form in one case, and 9 times in a different case?

. You are describing a content type (the logical equivalent of a record) with variable number of fields? That's not how it works.

• The content type definition dialogs are intended for a system administrator (not visitors to your site).
• A cardinality of unlimited does not mean variable per node instance. That's the issue.

Why not just implement the classic solution. 2 related content types. The logical equivalent of 2 related records (one to many).

Perhaps you can elaborate. Do you mean the system administrator defines a content type with 20 "class" fields (note 20 is static across all instances of that content type, not variable). What you could do is vary the display? My opinion that's a questionable approach at best. Now each instance of the content type (node) has to process 20 "class" fields. In the classic approach, the system only carries the number of "classes" as needed. Thus, I recommend re-architect to the standard solution.

Perhaps you can elaborate:)

Can't believe that it's not possible to change the cardinality of the field of a content-type programatically?!?!?

I am a total novice at D7, but this is a thought - suppose you want to "pre-click" the "add one more field" button 3 times. Can you create 4 separate text fields, with 3 of them having a cardinality of 1, and the 4th one having an unlimited cardinality?

I've been pondering the same problem and just found this: http://drupal.org/node/1592814
Maybe it's the widget you need to alter, not the form?

I have a content type "animal", content administrator will save animals, each animal has to be evaluated (1-5) on different aspects from a taxonomy term.

This is totally posible creating new content type relating each animal with taxonomy term and its value but the challenge is having the edit form for animal having all the taxonomy terms with the input text field for value (1-5).

I'm trying with field collection and i want to alter the form to repeat rows as many taxonomy terms i have showing only one checkbox according to delta value (checked and hidden).

Related: How to change field cardinality per form either programatically or by rule?

db_query("UPDATE field_config SET cardinality = 5 WHERE field_name = 'FIELD_NAME');
field_cache_clear();