I am creating a custom module with its own schema of a few tables. These tables need to have some values pre-populated into them for the module to work (default locations, select options, etc).

What's the best practices way to insert default values into these tables during hook_install?

Since drupal_write_record is not available, I can use db_query, but I just want to make sure that I'm not breaking any cardinal rules by doing so.


The better way is to do it inside hook_enable(); at the time the hook is invoked, the module is already installed, and the schema of its database is available to Drupal, and to drupal_write_record(). As the hook is invoked all times a module is enabled, and not just when the module is installed, the hook implementation should check if it didn't added those database rows already (e.g., it should use a Drupal variable containing a boolean value).

As example of module that uses hook_enable() for a similar purpose, you can check forum_enable(), or php_enable() (which adds the "PHP code" input format).

function php_enable() {
  $format_exists = (bool) db_query_range('SELECT 1 FROM {filter_format} WHERE name = :name', 0, 1, array(':name' => 'PHP code'))->fetchField();
  // Add a PHP code text format, if it does not exist. Do this only for the
  // first install (or if the format has been manually deleted) as there is no
  // reliable method to identify the format in an uninstall hook or in
  // subsequent clean installs.
  if (!$format_exists) {
    $php_format = array(
      'format' => 'php_code', 
      'name' => 'PHP code',
      // 'Plain text' format is installed with a weight of 10 by default. Use a
      // higher weight here to ensure that this format will not be the default
      // format for anyone. 
      'weight' => 11, 
      'filters' => array(
        // Enable the PHP evaluator filter.
        'php_code' => array(
          'weight' => 0, 
          'status' => 1,
    $php_format = (object) $php_format;

    drupal_set_message(t('A <a href="@php-code">PHP code</a> text format has been created.', array('@php-code' => url('admin/config/content/formats/' . $php_format->format))));

As shown from those hook implementations, the code could necessarily need to be executed all times the hook is executed; it could also be the code needs to just executed once, as in the case the default values added to the database cannot be altered from the user, who doesn't have a user interface to alter/delete those values.

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  • If I did this in hook_enable(), that means the default values would be reset every time that the module is enabled and disabled. I think that is fairly common, as opposed to completely un-installing and re-installing (at which point it is expected that the database gets reset). – oranges13 Aug 17 '11 at 14:22
  • 1
    That is why I wrote, "the hook implementation should check if it didn't add those database rows already." This means that it should check if the values are already in the database table, or use a Drupal variable to check if it is has already done that task. Checking the database table would be done if those values necessarily needs to be in the database; for example, this is the case if the values are required from the module, and the users are not allowed to remove the default values. – kiamlaluno Aug 17 '11 at 14:40
  • Thanks for the clarification. Is there any difference in storing these values in my own custom table vs. just using variable_set to store them in a persistent variable? It's just an array of values for custom select boxes. – oranges13 Aug 17 '11 at 14:43
  • All the values set using variable_set(), which are not deleted with variable_del(), are loaded in memory when Drupal bootstraps, and saved in a global variable; this means that they are in memory whatever the module is using those values, or not. Using a custom database table, you can be sure those values are only loaded when the module really needs it. You should not use variable_set() if the Drupal variable contains an array to which you keep adding a new array index all times, for example. – kiamlaluno Aug 17 '11 at 14:49
  • Looking at the code (D7). I only see 2 lines of code between the invocation of hook_install and hook_enable: an update to a local variable and a call to watchdog. So, during a real install, there is no difference whatsoever between these 2 hooks about what is available and registered and what not. The only difference is whether this is a first time install or just re-enabling the module. – fietserwin Jun 30 '12 at 19:46

I'd go with db_query / db_insert (D6 / D7) in hook_install().

It's not considered bad practice (and nobody is ever forcing you to use drupal_write_record()).

It is not uncommon for people to disable and re-enable modules, and in that case your code in hook_enable() would fire each time. which is not nice.

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