Change field type with hook_update_n for a module [duplicate]

Question

Hello I need to update the field type of one of my content types. The content type is of a module so I need to do this with the Drupal API for let users update the module for their 7.x-1.0 branch.

This is the hook for update the field, I need to change it from Integer to Decimal like this:

 /**
 * Change field_inq_description field from Integer to Decimal
 */
function field_updates_update_7100() {
  // Manual database changes.
  db_query("UPDATE {field_config} SET type = 'number_decimal' WHERE field_name = 'field_rin'");
  db_change_field('field_data_field_rin', 'field_rin_value', 'field_rin_value', array(
    'type' => 'numeric',
    'precision' => '10',
    'scale' => '2',
  ));
  db_change_field('field_revision_field_rin', 'field_rin_value', 'field_rin_value', array(
    'type' => 'numeric',
    'precision' => '10',
    'scale' => '2',
  ));
  // Clear caches.
  field_cache_clear(TRUE);
  // Apply the new field instance configuration.
}

After I apply the update with update.php script I get these notices everywhere in the test website.

Notice: Undefined index: precision in number_field_schema() (line 35 of /home/servilla/public_html/servillantasgiraldo.com.co/modules/field/modules/number/number.install).
Notice: Undefined index: scale in number_field_schema() (line 36 of /home/servilla/public_html/servillantasgiraldo.com.co/modules/field/modules/number/number.install).

What Im I doing wrong?

Answer 1

You just need to add precision and scale to the field config settings:

// API way.
$field = field_info_field('field_rin');
$field['settings']['precision'] = 10;
$field['settings']['scale'] = 2;
field_update_field($field);

// Raw way (shorthand, you'll want to add error checking).
$data = unserialize(db_query("SELECT data FROM {field_config} WHERE field_name = 'field_rin'")->fetchField());
$data['settings']['precision'] = 10;
$data['settings']['scale'] = 2;

db_update('field_config')
  ->fields(array('data' => serialize($data)))
  ->condition('field_name', 'field_rin')
  ->execute();

Answer 2

I found the answer, the help of Clive was great. Look this is the final code:

/**
 * Change field_inq_description field from Integer to Decimal
 */
function field_updates_update_7104() {
  // Manual database changes.
  db_query("UPDATE {field_config} SET type = 'number_decimal' WHERE field_name = 'field_rin'");
  db_change_field('field_data_field_rin', 'field_rin_value', 'field_rin_value', array(
    'type' => 'numeric',
    'precision' => '10',
    'scale' => '2',
  ));
  db_change_field('field_revision_field_rin', 'field_rin_value', 'field_rin_value', array(
    'type' => 'numeric',
    'precision' => '10',
    'scale' => '2',
  ));

    // Doing it with the raw way is the best choice.
    $data = unserialize(db_query("SELECT data FROM {field_config} WHERE field_name = 'field_rin'")->fetchField());
    $data['settings']['precision'] = 10;
    $data['settings']['scale'] = 2;

    db_update('field_config')
    ->fields(array('data' => serialize($data)))
    ->condition('field_name', 'field_rin')
    ->execute();

  // Clear caches.
  field_cache_clear(TRUE);

If you do it with the API way clive suggested and if you already have nodes of that content type the update.php script will show you an sql error telling you that you cannot update field properties with existing data, So the raw way clive suggested is the best way for do it. Thanks to Clive