node.module

<?php
// $Id$

/**
 * @file
 * The core that allows content to be submitted to the site. Modules and
 * scripts may programmatically submit nodes using the usual form API pattern.
 */

/**
 * Node is not published.
 */
define('NODE_NOT_PUBLISHED', 0);

/**
 * Node is published.
 */
define('NODE_PUBLISHED', 1);

/**
 * Node is not promoted to front page.
 */
define('NODE_NOT_PROMOTED', 0);

/**
 * Node is promoted to front page.
 */
define('NODE_PROMOTED', 1);

/**
 * Node is not sticky at top of the page.
 */
define('NODE_NOT_STICKY', 0);

/**
 * Node is sticky at top of the page.
 */
define('NODE_STICKY', 1);

/**
 * Nodes changed before this time are always marked as read.
 *
 * Nodes changed after this time may be marked new, updated, or read, depending
 * on their state for the current user. Defaults to 30 days ago.
 */
define('NODE_NEW_LIMIT', REQUEST_TIME - 30 * 24 * 60 * 60);

/**
 * Modules should return this value from hook_node_access() to allow access to a node.
 */
define('NODE_ACCESS_ALLOW', 'allow');

/**
 * Modules should return this value from hook_node_access() to deny access to a node.
 */
define('NODE_ACCESS_DENY', 'deny');

/**
 * Modules should return this value from hook_node_access() to not affect node access.
 */
define('NODE_ACCESS_IGNORE', NULL);

/**
 * Implements hook_help().
 */
function node_help($path, $arg) {
  // Remind site administrators about the {node_access} table being flagged
  // for rebuild. We don't need to issue the message on the confirm form, or
  // while the rebuild is being processed.
  if ($path != 'admin/reports/status/rebuild' && $path != 'batch' && strpos($path, '#') === FALSE
      && user_access('access administration pages') && node_access_needs_rebuild()) {
    if ($path == 'admin/reports/status') {
      $message = t('The content access permissions need to be rebuilt.');
    }
    else {
      $message = t('The content access permissions need to be rebuilt. <a href="@node_access_rebuild">Rebuild permissions</a>.', array('@node_access_rebuild' => url('admin/reports/status/rebuild')));
    }
    drupal_set_message($message, 'error');
  }

  switch ($path) {
    case 'admin/help#node':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Node module manages the creation, editing, deletion, settings, and display of the main site content. Content items managed by the Node module are typically displayed as pages on your site, and include a title, some meta-data (author, creation time, content type, etc.), and optional fields containing text or other data (fields are managed by the <a href="@field">Field module</a>). For more information, see the online handbook entry for <a href="@node">Node module</a>.', array('@node' => 'http://drupal.org/handbook/modules/node', '@field' => url('admin/help/field'))) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Creating content') . '</dt>';
      $output .= '<dd>' . t('When new content is created, the Node module records basic information about the content, including the author, date of creation, and the <a href="@content-type">Content type</a>. It also manages the <em>publishing options</em>, which define whether or not the content is published, promoted to the front page of the site, and/or sticky at the top of content lists. Default settings can be configured for each <a href="@content-type">type of content</a> on your site.', array('@content-type' => url('admin/structure/types'))) . '</dd>';
      $output .= '<dt>' . t('Creating custom content types') . '</dt>';
      $output .= '<dd>' . t('The Node module gives users with the <em>Administer content types</em> permission the ability to <a href="@content-new">create new content types</a> in addition to the default ones already configured. Creating custom content types allows you the flexibility to add <a href="@field">fields</a> and configure default settings that suit the differing needs of various site content.', array('@content-new' => url('admin/structure/types/add'), '@field' => url('admin/help/field'))) . '</dd>';
      $output .= '<dt>' . t('Administering content') . '</dt>';
      $output .= '<dd>' . t('The <a href="@content">Content administration page</a> allows you to review and bulk manage your site content.', array('@content' => url('admin/content'))) . '</dd>';
      $output .= '<dt>' . t('Creating revisions') . '</dt>';
      $output .= '<dd>' . t('The Node module also enables you to create multiple versions of any content, and revert to older versions using the <em>Revision information</em> settings.') . '</dd>';
      $output .= '<dt>' . t('User permissions') . '</dt>';
      $output .= '<dd>' . t('The Node module makes a number of permissions available for each content type, which can be set by role on the <a href="@permissions">permissions page</a>.', array('@permissions' => url('admin/people/permissions', array('fragment' => 'module-node')))) . '</dd>';
      $output .= '</dl>';
      return $output;

    case 'admin/structure/types/add':
      return '<p>' . t('Individual content types can have different fields, behaviors, and permissions assigned to them.') . '</p>';

    case 'admin/structure/types/manage/%/display':
      return '<p>' . t('Content items can be displayed using different view modes: Teaser, Full content, Print, RSS, etc. <em>Teaser</em> is a short format that is typically used in lists of multiple content items. <em>Full content</em> is typically used when the content is displayed on its own page.') . '</p>' .
        '<p>' . t('Here, you can define which fields are shown and hidden when %type content is displayed in each view mode, and define how the fields are displayed in each view mode.', array('%type' => node_type_get_name($arg[4]))) . '</p>';

    case 'node/%/revisions':
      return '<p>' . t('Revisions allow you to track differences between multiple versions of your content, and revert back to older versions.') . '</p>';

    case 'node/%/edit':
      $node = node_load($arg[1]);
      $type = node_type_get_type($node);
      return (!empty($type->help) ? '<p>' . filter_xss_admin($type->help) . '</p>' : '');
  }

  if ($arg[0] == 'node' && $arg[1] == 'add' && $arg[2]) {
    $type = node_type_get_type(str_replace('-', '_', $arg[2]));
    return (!empty($type->help) ? '<p>' . filter_xss_admin($type->help) . '</p>' : '');
  }
}

/**
 * Implements hook_theme().
 */
function node_theme() {
  return array(
    'node' => array(
      'render element' => 'elements',
      'template' => 'node',
    ),
    'node_list' => array(
      'variables' => array('items' => NULL, 'title' => NULL),
    ),
    'node_search_admin' => array(
      'render element' => 'form',
    ),
    'node_filters' => array(
      'render element' => 'form',
      'file' => 'node.admin.inc',
    ),
    'node_add_list' => array(
      'variables' => array('content' => NULL),
      'file' => 'node.pages.inc',
    ),
    'node_form' => array(
      'render element' => 'form',
      'file' => 'node.pages.inc',
    ),
    'node_preview' => array(
      'variables' => array('node' => NULL),
      'file' => 'node.pages.inc',
    ),
    'node_log_message' => array(
      'variables' => array('log' => NULL),
    ),
    'node_admin_overview' => array(
      'variables' => array('name' => NULL, 'type' => NULL),
    ),
    'node_recent_block' => array(
      'variables' => array('nodes' => NULL),
    ),
    'node_recent_content' => array(
      'variables' => array('node' => NULL),
    ),
  );
}

/**
 * Implements hook_cron().
 */
function node_cron() {
  db_delete('history')
    ->condition('timestamp', NODE_NEW_LIMIT, '<')
    ->execute();
}

/**
 * Implements hook_entity_info().
 */
function node_entity_info() {
  $return = array(
    'node' => array(
      'label' => t('Node'),
      'controller class' => 'NodeController',
      'base table' => 'node',
      'revision table' => 'node_revision',
      'uri callback' => 'node_uri',
      'fieldable' => TRUE,
      'object keys' => array(
        'id' => 'nid',
        'revision' => 'vid',
        'bundle' => 'type',
      ),
      'bundle keys' => array(
        'bundle' => 'type',
      ),
      // Node.module handles its own caching.
      // 'cacheable' => FALSE,
      'bundles' => array(),
      'view modes' => array(
        'full' => array(
          'label' => t('Full content'),
        ),
        'teaser' => array(
          'label' => t('Teaser'),
        ),
        'rss' => array(
          'label' => t('RSS'),
        ),
      ),
    ),
  );

  // Search integration is provided by node.module, so search-related
  // view modes for nodes are defined here and not in search.module.
  if (module_exists('search')) {
    $return['node']['view modes'] += array(
      'search_index' => array(
        'label' => t('Search index'),
      ),
      'search_result' => array(
        'label' => t('Search result'),
      ),
    );
  }

  // Bundles must provide a human readable name so we can create help and error
  // messages, and the path to attach Field admin pages to.
  foreach (node_type_get_names() as $type => $name) {
    $return['node']['bundles'][$type] = array(
      'label' => $name,
      'admin' => array(
        'path' => 'admin/structure/types/manage/%node_type',
        'real path' => 'admin/structure/types/manage/' . str_replace('_', '-', $type),
        'bundle argument' => 4,
        'access arguments' => array('administer content types'),
      ),
    );
  }

  return $return;
}

/**
 * Entity uri callback.
 */
function node_uri($node) {
  return array(
    'path' => 'node/' . $node->nid,
  );
}

/**
 * Implements hook_admin_paths().
 */
function node_admin_paths() {
  $paths = array(
    'node/*/edit' => TRUE,
    'node/*/delete' => TRUE,
    'node/*/revisions' => TRUE,
    'node/*/revisions/*/revert' => TRUE,
    'node/*/revisions/*/delete' => TRUE,
    'node/add' => TRUE,
    'node/add/*' => TRUE,
  );
  return $paths;
}

/**
 * Gather a listing of links to nodes.
 *
 * @param $result
 *   A DB result object from a query to fetch node entities. If your query
 *   joins the <code>node_comment_statistics</code> table so that the
 *   <code>comment_count</code> field is available, a title attribute will
 *   be added to show the number of comments.
 * @param $title
 *   A heading for the resulting list.
 *
 * @return
 *   An HTML list suitable as content for a block, or FALSE if no result can
 *   fetch from DB result object.
 */
function node_title_list($result, $title = NULL) {
  $items = array();
  $num_rows = FALSE;
  foreach ($result as $node) {
    $items[] = l($node->title, 'node/' . $node->nid, !empty($node->comment_count) ? array('attributes' => array('title' => format_plural($node->comment_count, '1 comment', '@count comments'))) : array());
    $num_rows = TRUE;
  }

  return $num_rows ? theme('node_list', array('items' => $items, 'title' => $title)) : FALSE;
}

/**
 * Format a listing of links to nodes.
 *
 * @ingroup themeable
 */
function theme_node_list($variables) {
  return theme('item_list', $variables);
}

/**
 * Update the 'last viewed' timestamp of the specified node for current user.
 *
 * @param $node
 *   A node object.
 */
function node_tag_new($node) {
  global $user;
  if ($user->uid) {
    db_merge('history')
      ->key(array(
        'uid' => $user->uid,
        'nid' => $node->nid,
      ))
      ->fields(array('timestamp' => REQUEST_TIME))
      ->execute();
   }
}

/**
 * Retrieves the timestamp at which the current user last viewed the
 * specified node.
 */
function node_last_viewed($nid) {
  global $user;
  $history = &drupal_static(__FUNCTION__, array());

  if (!isset($history[$nid])) {
    $history[$nid] = db_query("SELECT timestamp FROM {history} WHERE uid = :uid AND nid = :nid", array(':uid' => $user->uid, ':nid' => $nid))->fetchObject();
  }

  return (isset($history[$nid]->timestamp) ? $history[$nid]->timestamp : 0);
}

/**
 * Decide on the type of marker to be displayed for a given node.
 *
 * @param $nid
 *   Node ID whose history supplies the "last viewed" timestamp.
 * @param $timestamp
 *   Time which is compared against node's "last viewed" timestamp.
 * @return
 *   One of the MARK constants.
 */
function node_mark($nid, $timestamp) {
  global $user;
  $cache = &drupal_static(__FUNCTION__, array());

  if (!$user->uid) {
    return MARK_READ;
  }
  if (!isset($cache[$nid])) {
    $cache[$nid] = node_last_viewed($nid);
  }
  if ($cache[$nid] == 0 && $timestamp > NODE_NEW_LIMIT) {
    return MARK_NEW;
  }
  elseif ($timestamp > $cache[$nid] && $timestamp > NODE_NEW_LIMIT) {
    return MARK_UPDATED;
  }
  return MARK_READ;
}

/**
 * Extract the type name.
 *
 * @param $node
 *   Either a string or object, containing the node type information.
 *
 * @return
 *   Node type of the passed in data.
 */
function _node_extract_type($node) {
  return is_object($node) ? $node->type : $node;
}

/**
 * Returns a list of all the available node types.
 *
 * @return
 *   An array of node types, keyed by the type.
 * @see node_type_get_type()
 */
function node_type_get_types() {
  return _node_types_build()->types;
}

/**
 * Returns the node type of the passed node or node type string.
 *
 * @param $node
 *   A node object or string that indicates the node type to return.
 *
 * @return
 *   A single node type, as an object, or FALSE if the node type is not found.
 *   The node type is an object containing fields from hook_node_info() return
 *   values, as well as the field 'type' (the machine-readable type) and other
 *   fields used internally and defined in _node_types_build() and
 *   node_type_set_defaults().
 *
 * @see hook_node_info();
 */
function node_type_get_type($node) {
  $type = _node_extract_type($node);
  $types = _node_types_build()->types;
  return isset($types[$type]) ? $types[$type] : FALSE;
}

/**
 * Returns the node type base of the passed node or node type string.
 *
 * The base indicates which module implement this node type and is used to
 * execute node type specific hooks.
 *
 * @see node_invoke()
 *
 * @param $node
 *   A node object or string that indicates the node type to return.
 * @return
 *   The node type base or FALSE if the node type is not found.
 */
function node_type_get_base($node) {
  $type = _node_extract_type($node);
  $types = _node_types_build()->types;
  return isset($types[$type]) && isset($types[$type]->base) ? $types[$type]->base : FALSE;
}

/**
 * Returns a list of available node names.
 *
 * @return
 *   An array of node type names, keyed by the type.
 */
function node_type_get_names() {
  return _node_types_build()->names;
}

/**
 * Returns the node type name of the passed node or node type string.
 *
 * @param $node
 *   A node object or string that indicates the node type to return.
 *
 * @return
 *   The node type name or FALSE if the node type is not found.
 */
function node_type_get_name($node) {
  $type = _node_extract_type($node);
  $types = _node_types_build()->names;
  return isset($types[$type]) ? $types[$type] : FALSE;
}

/**
 * Resets the database cache of node types.
 *
 * All new or non-modified module-defined node types are saved to the database.
 */
function node_types_rebuild() {
  // Reset and load updated node types.
  drupal_static_reset('_node_types_build');
  foreach (node_type_get_types() as $type => $info) {
    if (!empty($info->is_new)) {
      node_type_save($info);
    }
    if (!empty($info->disabled)) {
      node_type_delete($info->type);
    }
  }
}

/**
 * Menu argument loader; Load a node type by string.
 *
 * @param $name
 *   The machine-readable name of a node type to load; having '_' replaced with
 *   '-'.
 *
 * @return
 *   A node type object or FALSE if $name does not exist.
 */
function node_type_load($name) {
  return node_type_get_type(strtr($name, array('-' => '_')));
}

/**
 * Saves a node type to the database.
 *
 * @param $info
 *   The node type to save, as an object.
 *
 * @return
 *   Status flag indicating outcome of the operation.
 */
function node_type_save($info) {
  $is_existing = FALSE;
  $existing_type = !empty($info->old_type) ? $info->old_type : $info->type;
  $is_existing = (bool) db_query_range('SELECT 1 FROM {node_type} WHERE type = :type', 0, 1, array(':type' => $existing_type))->fetchField();
  $type = node_type_set_defaults($info);

  $fields = array(
    'type' => (string) $type->type,
    'name' => (string) $type->name,
    'base' => (string) $type->base,
    'has_title' => (int) $type->has_title,
    'title_label' => (string) $type->title_label,
    'has_body' => (int) $type->has_body,
    'body_label' => (string) $type->body_label,
    'description' => (string) $type->description,
    'help' => (string) $type->help,
    'custom' => (int) $type->custom,
    'modified' => (int) $type->modified,
    'locked' => (int) $type->locked,
  );

  if ($is_existing) {
    db_update('node_type')
      ->fields($fields)
      ->condition('type', $existing_type)
      ->execute();

    if (!empty($type->old_type) && $type->old_type != $type->type) {
      field_attach_rename_bundle('node', $type->old_type, $type->type);
    }
    node_configure_fields($type);
    module_invoke_all('node_type_update', $type);
    $status = SAVED_UPDATED;
  }
  else {
    $fields['orig_type'] = (string) $type->orig_type;
    db_insert('node_type')
      ->fields($fields)
      ->execute();

    field_attach_create_bundle('node', $type->type);
    node_configure_fields($type);
    module_invoke_all('node_type_insert', $type);
    $status = SAVED_NEW;
  }

  // Clear the node type cache.
  drupal_static_reset('_node_types_build');

  return $status;
}

/**
 * Manage the field(s) for a node type.
 *
 * Currently, the node module manages a single Field API field,
 * 'body'.  If $type->has_body is true, this function ensures the
 * 'body' field exists and creates an instance of it for the bundle
 * $type->type (e.g. 'page', 'story', ...).  If $type->has_body is
 * false, this function removes the instance (if it exists) for the
 * 'body' field on $type->type.
 */
function node_configure_fields($type) {
   // Add or remove the body field, as needed.
  $field = field_info_field('body');
  $instance = field_info_instance('node', 'body', $type->type);
  if ($type->has_body) {
    if (empty($field)) {
      $field = array(
        'field_name' => 'body',
        'type' => 'text_with_summary',
        'object_types' => array('node'),
        'translatable' => TRUE,
      );
      $field = field_create_field($field);
    }
    if (empty($instance)) {
      $instance = array(
        'field_name' => 'body',
        'object_type' => 'node',
        'bundle' => $type->type,
        'label' => $type->body_label,
        'widget_type' => 'text_textarea_with_summary',
        'settings' => array('display_summary' => TRUE),

        // Define default formatters for the teaser and full view.
        'display' => array(
          'full' => array(
            'label' => 'hidden',
            'type' => 'text_default',
          ),
          'teaser' => array(
            'label' => 'hidden',
            'type' => 'text_summary_or_trimmed',
          ),
        ),
      );
      field_create_instance($instance);
    }
    else {
      $instance['label'] = $type->body_label;
      $instance['settings']['display_summary'] = TRUE;
      field_update_instance($instance);
    }
  }
  elseif (!empty($instance)) {
    field_delete_instance($instance);
  }
}

/**
 * Implements hook_field_extra_fields().
 */
function node_field_extra_fields() {
  $extra = array();

  foreach (node_type_get_types() as $type) {
    if ($type->has_title) {
      $extra['node'][$type->type] = array(
        'title' => array(
          'label' => $type->title_label,
          'description' => t('Node module element.'),
          'weight' => -5,
        ),
      );
    }
  }

  return $extra;
}

/**
 * Deletes a node type from the database.
 *
 * @param $type
 *   The machine-readable name of the node type to be deleted.
 */
function node_type_delete($type) {
  $info = node_type_get_type($type);
  db_delete('node_type')
    ->condition('type', $type)
    ->execute();
  module_invoke_all('node_type_delete', $info);

  // Clear the node type cache.
  drupal_static_reset('_node_types_build');
}

/**
 * Updates all nodes of one type to be of another type.
 *
 * @param $old_type
 *   The current node type of the nodes.
 * @param $type
 *   The new node type of the nodes.
 *
 * @return
 *   The number of nodes whose node type field was modified.
 */
function node_type_update_nodes($old_type, $type) {
  return db_update('node')
    ->fields(array('type' => $type))
    ->condition('type', $old_type)
    ->execute();
}

/**
 * Builds and returns the list of available node types.
 *
 * The list of types is built by querying hook_node_info() in all modules, and
 * by comparing this information with the node types in the {node_type} table.
 *
 */
function _node_types_build() {
  $_node_types = &drupal_static(__FUNCTION__);
  if (is_object($_node_types)) {
    return $_node_types;
  }
  $_node_types = (object)array('types' => array(), 'names' => array());

  $info_array = module_invoke_all('node_info');
  foreach ($info_array as $type => $info) {
    $info['type'] = $type;
    $_node_types->types[$type] = node_type_set_defaults($info);
    $_node_types->names[$type] = $info['name'];
  }
  $type_result = db_select('node_type', 'nt')
    ->addTag('translatable')
    ->addTag('node_type_access')
    ->fields('nt')
    ->orderBy('nt.type', 'ASC')
    ->execute();
  foreach ($type_result as $type_object) {
    // Check for node types from disabled modules and mark their types for removal.
    // Types defined by the node module in the database (rather than by a separate
    // module using hook_node_info) have a base value of 'node_content'. The isset()
    // check prevents errors on old (pre-Drupal 7) databases.
    if (isset($type_object->base) && $type_object->base != 'node_content' && empty($info_array[$type_object->type])) {
      $type_object->disabled = TRUE;
    }
    if (!isset($_node_types->types[$type_object->type]) || $type_object->modified) {
      $_node_types->types[$type_object->type] = $type_object;
      $_node_types->names[$type_object->type] = $type_object->name;

      if ($type_object->type != $type_object->orig_type) {
        unset($_node_types->types[$type_object->orig_type]);
        unset($_node_types->names[$type_object->orig_type]);
      }
    }
  }

  asort($_node_types->names);

  return $_node_types;
}

/**
 * Set the default values for a node type.
 *
 * The defaults are for a type defined through hook_node_info().
 * When populating a custom node type $info should have the 'custom'
 * key set to 1.
 *
 * @param $info
 *   An object or array containing values to override the defaults.
 *
 * @return
 *  A node type object.
 */
function node_type_set_defaults($info = array()) {
  $type = &drupal_static(__FUNCTION__);

  if (!isset($type)) {
    $type = new stdClass();
    $type->type = '';
    $type->name = '';
    $type->base = '';
    $type->description = '';
    $type->help = '';
    $type->has_title = 1;
    $type->has_body = 1;
    $type->title_label = t('Title');
    $type->body_label = t('Body');
    $type->custom = 0;
    $type->modified = 0;
    $type->locked = 1;
    $type->is_new = 1;
  }

  $new_type = clone $type;
  $info = (array) $info;
  foreach ($info as $key => $data) {
    $new_type->$key = $data;
  }
  // If the type has no title or body, set an empty label.
  if (!$new_type->has_title) {
    $new_type->title_label = '';
  }
  if (!$new_type->has_body) {
    $new_type->body_label = '';
  }
  $new_type->orig_type = isset($info['type']) ? $info['type'] : '';

  return $new_type;
}

/**
 * Implements hook_rdf_mapping().
 */
function node_rdf_mapping() {
  return array(
    array(
      'type' => 'node',
      'bundle' => RDF_DEFAULT_BUNDLE,
      'mapping' => array(
        'rdftype' => array('sioc:Item', 'foaf:Document'),
        'title' => array(
          'predicates' => array('dc:title'),
        ),
        'created' => array(
          'predicates' => array('dc:date', 'dc:created'),
          'datatype' => 'xsd:dateTime',
          'callback' => 'date_iso8601',
        ),
        'changed' => array(
          'predicates' => array('dc:modified'),
          'datatype' => 'xsd:dateTime',
          'callback' => 'date_iso8601',
        ),
        'body' => array(
          'predicates' => array('content:encoded'),
        ),
        'uid' => array(
          'predicates' => array('sioc:has_creator'),
          'type' => 'rel',
        ),
        'name' => array(
          'predicates' => array('foaf:name'),
        ),
        'comment_count' => array(
          'predicates' => array('sioc:num_replies'),
          'datatype' => 'xsd:integer',
        ),
        'last_activity' => array(
          'predicates' => array('sioc:last_activity_date'),
          'datatype' => 'xsd:dateTime',
          'callback' => 'date_iso8601',
        ),
      ),
    ),
  );
}

/**
 * Determine whether a node hook exists.
 *
 * @param $node
 *   A node object or a string containing the node type.
 * @param $hook
 *   A string containing the name of the hook.
 * @return
 *   TRUE if the $hook exists in the node type of $node.
 */
function node_hook($node, $hook) {
  $base = node_type_get_base($node);
  return module_hook($base, $hook);
}

/**
 * Invoke a node hook.
 *
 * @param $node
 *   A node object or a string containing the node type.
 * @param $hook
 *   A string containing the name of the hook.
 * @param $a2, $a3, $a4
 *   Arguments to pass on to the hook, after the $node argument.
 * @return
 *   The returned value of the invoked hook.
 */
function node_invoke($node, $hook, $a2 = NULL, $a3 = NULL, $a4 = NULL) {
  if (node_hook($node, $hook)) {
    $base = node_type_get_base($node);
    $function = $base . '_' . $hook;
    return ($function($node, $a2, $a3, $a4));
  }
}

/**
 * Load node entities from the database.
 *
 * This function should be used whenever you need to load more than one node
 * from the database. Nodes are loaded into memory and will not require
 * database access if loaded again during the same page request.
 *
 * @see entity_load()
 *
 * @param $nids
 *   An array of node IDs.
 * @param $conditions
 *   An array of conditions on the {node} table in the form 'field' => $value.
 * @param $reset
 *   Whether to reset the internal node_load cache.
 *
 * @return
 *   An array of node objects indexed by nid.
 */
function node_load_multiple($nids = array(), $conditions = array(), $reset = FALSE) {
  return entity_load('node', $nids, $conditions, $reset);
}

/**
 * Load a node object from the database.
 *
 * @param $nid
 *   The node ID.
 * @param $vid
 *   The revision ID.
 * @param $reset
 *   Whether to reset the node_load_multiple cache.
 *
 * @return
 *   A fully-populated node object.
 */
function node_load($nid = NULL, $vid = NULL, $reset = FALSE) {
  $nids = (isset($nid) ? array($nid) : array());
  $conditions = (isset($vid) ? array('vid' => $vid) : array());
  $node = node_load_multiple($nids, $conditions, $reset);
  return $node ? reset($node) : FALSE;
}

/**
 * Perform validation checks on the given node.
 */
function node_validate($node, $form = array()) {
  $type = node_type_get_type($node);

  if (isset($node->nid) && (node_last_changed($node->nid) > $node->changed)) {
    form_set_error('changed', t('The content on this page has either been modified by another user, or you have already submitted modifications using this form. As a result, your changes cannot be saved.'));
  }

  // Validate the "authored by" field.
  if (!empty($node->name) && !($account = user_load_by_name($node->name))) {
    // The use of empty() is mandatory in the context of usernames
    // as the empty string denotes the anonymous user. In case we
    // are dealing with an anonymous user we set the user ID to 0.
    form_set_error('name', t('The username %name does not exist.', array('%name' => $node->name)));
  }

  // Validate the "authored on" field.
  if (!empty($node->date) && strtotime($node->date) === FALSE) {
    form_set_error('date', t('You have to specify a valid date.'));
  }

  // Do node-type-specific validation checks.
  node_invoke($node, 'validate', $form);
  module_invoke_all('node_validate', $node, $form);
}

/**
 * Prepare node for saving by populating author and creation date.
 */
function node_submit($node) {
  global $user;

  // A user might assign the node author by entering a user name in the node
  // form, which we then need to translate to a user ID.
  if (isset($node->name)) {
    if ($account = user_load_by_name($node->name)) {
      $node->uid = $account->uid;
    }
    else {
      $node->uid = 0;
    }
  }

  $node->created = !empty($node->date) ? strtotime($node->date) : REQUEST_TIME;
  $node->validated = TRUE;

  return $node;
}

/**
 * Save changes to a node or add a new node.
 *
 * @param $node
 *   The $node object to be saved. If $node->nid is
 *   omitted (or $node->is_new is TRUE), a new node will be added.
 */
function node_save($node) {
  $transaction = db_transaction();