1 update.inc update_build_dependency_graph($update_functions)

Constructs a graph which encodes the dependencies between module updates.

This function returns an associative array which contains a "directed graph" representation of the dependencies between a provided list of update functions, as well as any outside update functions that they directly depend on but that were not in the provided list. The vertices of the graph represent the update functions themselves, and each edge represents a requirement that the first update function needs to run before the second. For example, consider this graph:

system_update_1000 ---> system_update_1001 ---> system_update_1002

Visually, this indicates that system_update_1000() must run before system_update_1001(), which in turn must run before system_update_1002().

The function takes into account standard dependencies within each module, as shown above (i.e., the fact that each module's updates must run in numerical order), but also finds any cross-module dependencies that are defined by modules which implement hook_update_dependencies(), and builds them into the graph as well.


$update_functions: An organized array of update functions, in the format returned by update_get_update_function_list().

Return value

A multidimensional array representing the dependency graph, suitable for: passing in to backdrop_depth_first_search(), but with extra information about each update function also included. Each array key contains the name of an update function, including all update functions from the provided list as well as any outside update functions which they directly depend on. Each value is an associative array containing the following keys:

  • 'edges': A representation of any other update functions that immediately depend on this one. See backdrop_depth_first_search() for more details on the format.
  • 'module': The name of the module that this update function belongs to.
  • 'number': The number of this update function within that module.

See also




core/includes/update.inc, line 949
Backdrop database update API.


function update_build_dependency_graph($update_functions) {
  // Initialize an array that will define a directed graph representing the
  // dependencies between update functions.
  $graph = array();

  // Go through each update function and build an initial list of dependencies.
  foreach ($update_functions as $module => $functions) {
    $previous_function = NULL;
    foreach ($functions as $number => $function) {
      // Add an edge to the directed graph representing the fact that each
      // update function in a given module must run after the update that
      // precedes it based on the provided order.
      if ($previous_function) {
        $graph[$previous_function]['edges'][$function] = TRUE;
      $previous_function = $function;

      // Define the module and update number associated with this function.
      $graph[$function]['module'] = $module;
      $graph[$function]['number'] = $number;

  // Now add any explicit update dependencies declared by modules.
  $update_dependencies = update_retrieve_dependencies();
  foreach ($graph as $function => $data) {
    if (!empty($update_dependencies[$data['module']][$data['number']])) {
      foreach ($update_dependencies[$data['module']][$data['number']] as $module => $number) {
        $dependency = $module . '_update_' . $number;
        $graph[$dependency]['edges'][$function] = TRUE;
        $graph[$dependency]['module'] = $module;
        $graph[$dependency]['number'] = $number;

  return $graph;