How to programmatically remove a field from a node?

Question

How does one remove a field from a node programmatically? I have a migration in hook_update_N that moves the contents from a a field into a custom table. After that migration, I want to remove the field in that same function.

Are there any field API's that cater removing fields?

Edit, Solution: Because the answers lack actual code, here is what I did to move fields from the $users into my own records and subsequently remove the field from the database;

function my_module_update_7005(&$sandbox) {
  $slice = 100;
  //Fetch users from database;
  if (!isset($sandbox['progress'])) {
    $sandbox['progress'] = 0;
    $sandbox['current_uid'] = 0;
    // We'll -1 to disregard the uid 0...
    $sandbox['max'] = db_query('SELECT COUNT(DISTINCT uid) FROM {users}')->fetchField() - 1;
  }
  if (empty($users)) {
    $sandbox["current_uid"] += $slice;
  }
  $users = db_select('users', 'u')
    ->fields('u', array('uid', 'name'))
    ->condition('uid', $sandbox['current_uid'], '>')
    ->range(0, $slice)
    ->orderBy('uid', 'ASC')
    ->execute();
  //Loop trough users;
  foreach ($users as $user) {
    $foo = new Foo();
    // Warning: drupal's fields return mixed values; e.g. NULL versus an int.
    $foo->debits = (int) $user->user()->field_credits["und"][0]["value"];
    $foo->save();

    $sandbox['progress']++;
    $sandbox['current_uid'] = $user->uid;
  }

  $sandbox['#finished'] = empty($sandbox['max']) ? 1 : ($sandbox['progress'] / $sandbox['max']);

  // Remove the field.
  field_delete_field("field_credits"); //note that the name for Foo is field_foo
  field_purge_batch($sandbox['max']+1);//Drupal seems to have an offbyone problem.
}

Answer 1

field_delete_field($field_name) will mark the $field_name for deletion on next cron run.

You could use field_purge_batch to do the deletion, if you don't want to do it on cron run.

EDIT: field_delete_field() should be used when you need to delete the field from other bundles as well. If you only wish to delete the field from a particular bundle you should use field_delete_instance() as mentioned by @Clive.

Answer 2

To remove a field from a particular bundle you can use field_delete_instance()

Marks a field instance and its data for deletion.

Example:

function my_module_update_7001() {
  if ($instance = field_info_instance('node', 'field_name', 'page'))  {
    field_delete_instance($instance, TRUE);
    field_purge_batch(1);
  }
}

To remove a field from the system completely, you can use field_delete_field()

Marks a field and its instances and data for deletion.

Example:

function my_module_update_7001() {
  field_delete_field('field_name');
  field_purge_batch(1);
}

The fields/instances are only marked for deletion, the data will actually be purged during subsequent cron runs. To purged it manually execute:

field_purge_batch(1);

Answer 3

To answer @berkes question:

field_delete_field() does mark the field for deletion, causing it to get purged on the next cron run. However it does leave data on field_config_instance regarding the dropped field. Running cron or field_purge_batch() will not remove this data from field_config_instance table, even if the deleted column is set to 1 for the field.

For me using field_delete_instance() followed by a field_purge_batch() for each purged field worked - instantly removing both the field from the database (without requiring cron), as well as purging the field_config_instance table of any field data (for the deleted field).

Here is the solution:

/**
 * Implements hook_uninstall().
 */
function hook_uninstall() {
  // Delete all fields for all xyz entity bundles.

  // Retrieve all bundles for an entity.
  $bundles = field_info_bundles('XYZ'); // The name of your entity type, for example, 'node'.
  foreach ($bundles as $bundle => $properties) {

    // Retrieve all the fields for a given bundle.
    $instances = field_info_instances('XYZ', $bundle);
    foreach ($instances as $instance) {
      field_delete_instance($instance, TRUE);
      field_purge_batch(1);
    }
  }
}

Do note the TRUE on field_delete_instance(), as it indicates that the Field API should perform cleanup operations.