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Drupal example source code file (select.inc)

This example Drupal source code file (select.inc) is included in the DevDaily.com "Drupal Source Code Warehouse" project. The intent of this project is to help you "Learn Drupal by Example".

PHP - Drupal tags/keywords

alias, as, direction, empty, field, foreach, function, if, php, public, return, string, table, table_field

The select.inc Drupal example source code

<?php
// $Id: select.inc,v 1.1 2010/11/29 19:57:57 webchick Exp $

/**
 * @file
 * Select builder for PostgreSQL database engine.
 */

/**
 * @ingroup database
 * @{
 */

class SelectQuery_pgsql extends SelectQuery {

  public function orderRandom() {
    $alias = $this->addExpression('RANDOM()', 'random_field');
    $this->orderBy($alias);
    return $this;
  }

  /**
   * Overrides SelectQuery::orderBy().
   *
   * PostgreSQL adheres strictly to the SQL-92 standard and requires that when
   * using DISTINCT or GROUP BY conditions, fields and expressions that are
   * ordered on also need to be selected. This is a best effort implementation
   * to handle the cases that can be automated by adding the field if it is not
   * yet selected.
   *
   * @code
   *   $query = db_select('node', 'n');
   *   $query->join('node_revision', 'nr', 'n.vid = nr.vid');
   *   $query
   *     ->distinct()
   *     ->fields('n')
   *     ->orderBy('timestamp');
   * @endcode
   *
   * In this query, it is not possible (without relying on the schema) to know
   * whether timestamp belongs to node_revisions and needs to be added or
   * belongs to node and is already selected. Queries like this will need to be
   * corrected in the original query by adding an explicit call to
   * SelectQuery::addField() or SelectQuery::fields().
   *
   * Since this has a small performance impact, both by the additional
   * processing in this function and in the database that needs to return the
   * additional fields, this is done as an override instead of implementing it
   * directly in SelectQuery::orderBy().
   */
  public function orderBy($field, $direction = 'ASC') {
    // Call parent function to order on this.
    $return = parent::orderBy($field, $direction);

    // If there is a table alias specified, split it up.
    if (strpos($field, '.') !== FALSE) {
      list($table, $table_field) = explode('.', $field);
    }
    // Figure out if the field has already been added.
    foreach ($this->fields as $existing_field) {
      if (!empty($table)) {
        // If table alias is given, check if field and table exists.
        if ($existing_field['table'] == $table && $existing_field['field'] == $table_field) {
          return $return;
        }
      }
      else {
        // If there is no table, simply check if the field exists as a field or
        // an aliased field.
        if ($existing_field['alias'] == $field) {
          return $return;
        }
      }
    }

    // Also check expression aliases.
    foreach ($this->expressions as $expression) {
      if ($expression['alias'] == $field) {
        return $return;
      }
    }

    // If a table loads all fields, it can not be added again. It would
    // result in an ambigious alias error because that field would be loaded
    // twice: Once through table_alias.* and once directly. If the field
    // actually belongs to a different table, it must be added manually.
    foreach ($this->tables as $table) {
      if (!empty($table['all_fields'])) {
        return $return;
      }
    }

    // If $field contains an characters which are not allowed in a field name
    // it is considered an expression, these can't be handeld automatically
    // either.
    if ($this->connection->escapeField($field) != $field) {
      return $return;
    }

    // This is a case that can be handled automatically, add the field.
    $this->addField(NULL, $field);
    return $return;
  }
}

/**
 * @} End of "ingroup database".
 */

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