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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, arguments, array, field, foreach, function, if, null, php, public, query, return, table, this

The select.inc Drupal example source code

<?php
// $Id: select.inc,v 1.59 2010/12/31 20:43:43 webchick Exp $

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

require_once dirname(__FILE__) . '/query.inc';

/**
 * Interface for extendable query objects.
 *
 * "Extenders" follow the "Decorator" OOP design pattern.  That is, they wrap
 * and "decorate" another object.  In our case, they implement the same interface
 * as select queries and wrap a select query, to which they delegate almost all
 * operations.  Subclasses of this class may implement additional methods or
 * override existing methods as appropriate.  Extenders may also wrap other
 * extender objects, allowing for arbitrarily complex "enhanced" queries.
 */
interface QueryExtendableInterface {

  /**
   * Enhance this object by wrapping it in an extender object.
   *
   * @param $extender_name
   *   The base name of the extending class.  The base name will be checked
   *   against the current database connection to allow driver-specific subclasses
   *   as well, using the same logic as the query objects themselves.  For example,
   *   PagerDefault_mysql is the MySQL-specific override for PagerDefault.
   * @return QueryExtendableInterface
   *   The extender object, which now contains a reference to this object.
   */
  public function extend($extender_name);
}

/**
 * Interface definition for a Select Query object.
 */
interface SelectQueryInterface extends QueryConditionInterface, QueryAlterableInterface, QueryExtendableInterface, QueryPlaceholderInterface {

  /* Alter accessors to expose the query data to alter hooks. */

  /**
   * Returns a reference to the fields array for this query.
   *
   * Because this method returns by reference, alter hooks may edit the fields
   * array directly to make their changes. If just adding fields, however, the
   * use of addField() is preferred.
   *
   * Note that this method must be called by reference as well:
   *
   * @code
   * $fields =& $query->getFields();
   * @endcode
   *
   * @return
   *   A reference to the fields array structure.
   */
  public function &getFields();

  /**
   * Returns a reference to the expressions array for this query.
   *
   * Because this method returns by reference, alter hooks may edit the expressions
   * array directly to make their changes. If just adding expressions, however, the
   * use of addExpression() is preferred.
   *
   * Note that this method must be called by reference as well:
   *
   * @code
   * $fields =& $query->getExpressions();
   * @endcode
   *
   * @return
   *   A reference to the expression array structure.
   */
  public function &getExpressions();

  /**
   * Returns a reference to the order by array for this query.
   *
   * Because this method returns by reference, alter hooks may edit the order-by
   * array directly to make their changes. If just adding additional ordering
   * fields, however, the use of orderBy() is preferred.
   *
   * Note that this method must be called by reference as well:
   *
   * @code
   * $fields =& $query->getOrderBy();
   * @endcode
   *
   * @return
   *   A reference to the expression array structure.
   */
  public function &getOrderBy();

  /**
   * Returns a reference to the group-by array for this query.
   *
   * Because this method returns by reference, alter hooks may edit the group-by
   * array directly to make their changes. If just adding additional grouping
   * fields, however, the use of groupBy() is preferred.
   *
   * Note that this method must be called by reference as well:
   *
   * @code
   * $fields =& $query->getGroupBy();
   * @endcode
   *
   * @return
   *   A reference to the group-by array structure.
   */
  public function &getGroupBy();

  /**
   * Returns a reference to the tables array for this query.
   *
   * Because this method returns by reference, alter hooks may edit the tables
   * array directly to make their changes. If just adding tables, however, the
   * use of the join() methods is preferred.
   *
   * Note that this method must be called by reference as well:
   *
   * @code
   * $fields =& $query->getTables();
   * @endcode
   *
   * @return
   *   A reference to the tables array structure.
   */
  public function &getTables();

  /**
   * Returns a reference to the union queries for this query. This include
   * queries for UNION, UNION ALL, and UNION DISTINCT.
   *
   * Because this method returns by reference, alter hooks may edit the tables
   * array directly to make their changes. If just adding union queries,
   * however, the use of the union() method is preferred.
   *
   * Note that this method must be called by reference as well:
   *
   * @code
   * $fields =& $query->getUnion();
   * @endcode
   *
   * @return
   *   A reference to the union query array structure.
   */
  public function &getUnion();

  /**
   * Compiles and returns an associative array of the arguments for this prepared statement.
   *
   * @param $queryPlaceholder
   *   When collecting the arguments of a subquery, the main placeholder
   *   object should be passed as this parameter.
   *
   * @return
   *   An associative array of all placeholder arguments for this query.
   */
  public function getArguments(QueryPlaceholderInterface $queryPlaceholder = NULL);

  /* Query building operations */

  /**
   * Sets this query to be DISTINCT.
   *
   * @param $distinct
   *   TRUE to flag this query DISTINCT, FALSE to disable it.
   * @return SelectQueryInterface
   *   The called object.
   */
  public function distinct($distinct = TRUE);

  /**
   * Adds a field to the list to be SELECTed.
   *
   * @param $table_alias
   *   The name of the table from which the field comes, as an alias. Generally
   *   you will want to use the return value of join() here to ensure that it is
   *   valid.
   * @param $field
   *   The name of the field.
   * @param $alias
   *   The alias for this field. If not specified, one will be generated
   *   automatically based on the $table_alias and $field. The alias will be
   *   checked for uniqueness, so the requested alias may not be the alias
   *   that is assigned in all cases.
   * @return
   *   The unique alias that was assigned for this field.
   */
  public function addField($table_alias, $field, $alias = NULL);

  /**
   * Add multiple fields from the same table to be SELECTed.
   *
   * This method does not return the aliases set for the passed fields. In the
   * majority of cases that is not a problem, as the alias will be the field
   * name. However, if you do need to know the alias you can call getFields()
   * and examine the result to determine what alias was created. Alternatively,
   * simply use addField() for the few fields you care about and this method for
   * the rest.
   *
   * @param $table_alias
   *   The name of the table from which the field comes, as an alias. Generally
   *   you will want to use the return value of join() here to ensure that it is
   *   valid.
   * @param $fields
   *   An indexed array of fields present in the specified table that should be
   *   included in this query. If not specified, $table_alias.* will be generated
   *   without any aliases.
   * @return SelectQueryInterface
   *   The called object.
   */
  public function fields($table_alias, array $fields = array());

  /**
   * Adds an expression to the list of "fields" to be SELECTed.
   *
   * An expression can be any arbitrary string that is valid SQL. That includes
   * various functions, which may in some cases be database-dependent. This
   * method makes no effort to correct for database-specific functions.
   *
   * @param $expression
   *   The expression string. May contain placeholders.
   * @param $alias
   *   The alias for this expression. If not specified, one will be generated
   *   automatically in the form "expression_#". The alias will be checked for
   *   uniqueness, so the requested alias may not be the alias that is assigned
   *   in all cases.
   * @param $arguments
   *   Any placeholder arguments needed for this expression.
   * @return
   *   The unique alias that was assigned for this expression.
   */
  public function addExpression($expression, $alias = NULL, $arguments = array());

  /**
   * Default Join against another table in the database.
   *
   * This method is a convenience method for innerJoin().
   *
   * @param $table
   *   The table against which to join.
   * @param $alias
   *   The alias for the table. In most cases this should be the first letter
   *   of the table, or the first letter of each "word" in the table.
   * @param $condition
   *   The condition on which to join this table. If the join requires values,
   *   this clause should use a named placeholder and the value or values to
   *   insert should be passed in the 4th parameter. For the first table joined
   *   on a query, this value is ignored as the first table is taken as the base
   *   table. The token %alias can be used in this string to be replaced with
   *   the actual alias. This is useful when $alias is modified by the database
   *   system, for example, when joining the same table more than once.
   * @param $arguments
   *   An array of arguments to replace into the $condition of this join.
   * @return
   *   The unique alias that was assigned for this table.
   */
  public function join($table, $alias = NULL, $condition = NULL, $arguments = array());

  /**
   * Inner Join against another table in the database.
   *
   * @param $table
   *   The table against which to join.
   * @param $alias
   *   The alias for the table. In most cases this should be the first letter
   *   of the table, or the first letter of each "word" in the table.
   * @param $condition
   *   The condition on which to join this table. If the join requires values,
   *   this clause should use a named placeholder and the value or values to
   *   insert should be passed in the 4th parameter. For the first table joined
   *   on a query, this value is ignored as the first table is taken as the base
   *   table. The token %alias can be used in this string to be replaced with
   *   the actual alias. This is useful when $alias is modified by the database
   *   system, for example, when joining the same table more than once.
   * @param $arguments
   *   An array of arguments to replace into the $condition of this join.
   * @return
   *   The unique alias that was assigned for this table.
   */
  public function innerJoin($table, $alias = NULL, $condition = NULL, $arguments = array());

  /**
   * Left Outer Join against another table in the database.
   *
   * @param $table
   *   The table against which to join.
   * @param $alias
   *   The alias for the table. In most cases this should be the first letter
   *   of the table, or the first letter of each "word" in the table.
   * @param $condition
   *   The condition on which to join this table. If the join requires values,
   *   this clause should use a named placeholder and the value or values to
   *   insert should be passed in the 4th parameter. For the first table joined
   *   on a query, this value is ignored as the first table is taken as the base
   *   table. The token %alias can be used in this string to be replaced with
   *   the actual alias. This is useful when $alias is modified by the database
   *   system, for example, when joining the same table more than once.
   * @param $arguments
   *   An array of arguments to replace into the $condition of this join.
   * @return
   *   The unique alias that was assigned for this table.
   */
  public function leftJoin($table, $alias = NULL, $condition = NULL, $arguments = array());

  /**
   * Right Outer Join against another table in the database.
   *
   * @param $table
   *   The table against which to join.
   * @param $alias
   *   The alias for the table. In most cases this should be the first letter
   *   of the table, or the first letter of each "word" in the table.
   * @param $condition
   *   The condition on which to join this table. If the join requires values,
   *   this clause should use a named placeholder and the value or values to
   *   insert should be passed in the 4th parameter. For the first table joined
   *   on a query, this value is ignored as the first table is taken as the base
   *   table. The token %alias can be used in this string to be replaced with
   *   the actual alias. This is useful when $alias is modified by the database
   *   system, for example, when joining the same table more than once.
   * @param $arguments
   *   An array of arguments to replace into the $condition of this join.
   * @return
   *   The unique alias that was assigned for this table.
   */
  public function rightJoin($table, $alias = NULL, $condition = NULL, $arguments = array());

  /**
   * Join against another table in the database.
   *
   * This method does the "hard" work of queuing up a table to be joined against.
   * In some cases, that may include dipping into the Schema API to find the necessary
   * fields on which to join.
   *
   * @param $type
   *   The type of join. Typically one one of INNER, LEFT OUTER, and RIGHT OUTER.
   * @param $table
   *   The table against which to join. May be a string or another SelectQuery
   *   object. If a query object is passed, it will be used as a subselect.
   * @param $alias
   *   The alias for the table. In most cases this should be the first letter
   *   of the table, or the first letter of each "word" in the table. If omitted,
   *   one will be dynamically generated.
   * @param $condition
   *   The condition on which to join this table. If the join requires values,
   *   this clause should use a named placeholder and the value or values to
   *   insert should be passed in the 4th parameter. For the first table joined
   *   on a query, this value is ignored as the first table is taken as the base
   *   table. The token %alias can be used in this string to be replaced with
   *   the actual alias. This is useful when $alias is modified by the database
   *   system, for example, when joining the same table more than once.
   * @param $arguments
   *   An array of arguments to replace into the $condition of this join.
   * @return
   *   The unique alias that was assigned for this table.
   */
  public function addJoin($type, $table, $alias = NULL, $condition = NULL, $arguments = array());

  /**
   * Orders the result set by a given field.
   *
   * If called multiple times, the query will order by each specified field in the
   * order this method is called.
   *
   * If the query uses DISTINCT or GROUP BY conditions, fields or expressions
   * that are used for the order must be selected to be compatible with some
   * databases like PostgreSQL. The PostgreSQL driver can handle simple cases
   * automatically but it is suggested to explicitly specify them. Additionally,
   * when ordering on an alias, the alias must be added before orderBy() is
   * called.
   *
   * @param $field
   *   The field on which to order.
   * @param $direction
   *   The direction to sort. Legal values are "ASC" and "DESC".
   * @return SelectQueryInterface
   *   The called object.
   */
  public function orderBy($field, $direction = 'ASC');

  /**
   * Orders the result set by a random value.
   *
   * This may be stacked with other orderBy() calls. If so, the query will order
   * by each specified field, including this one, in the order called. Although
   * this method may be called multiple times on the same query, doing so
   * is not particularly useful.
   *
   * Note: The method used by most drivers may not scale to very large result
   * sets. If you need to work with extremely large data sets, you may create
   * your own database driver by subclassing off of an existing driver and
   * implementing your own randomization mechanism. See
   *
   * http://jan.kneschke.de/projects/mysql/order-by-rand/
   *
   * for an example of such an alternate sorting mechanism.
   *
   * @return SelectQueryInterface
   *   The called object
   */
  public function orderRandom();

  /**
   * Restricts a query to a given range in the result set.
   *
   * If this method is called with no parameters, will remove any range
   * directives that have been set.
   *
   * @param $start
   *   The first record from the result set to return. If NULL, removes any
   *   range directives that are set.
   * @param $limit
   *   The number of records to return from the result set.
   * @return SelectQueryInterface
   *   The called object.
   */
  public function range($start = NULL, $length = NULL);

  /**
   * Add another Select query to UNION to this one.
   *
   * Union queries consist of two or more queries whose
   * results are effectively concatenated together. Queries
   * will be UNIONed in the order they are specified, with
   * this object's query coming first. Duplicate columns will
   * be discarded. All forms of UNION are supported, using
   * the second '$type' argument.
   *
   * Note: All queries UNIONed together must have the same
   * field structure, in the same order. It is up to the
   * caller to ensure that they match properly. If they do
   * not, an SQL syntax error will result.
   *
   * @param $query
   *   The query to UNION to this query.
   * @param $type
   *   The type of UNION to add to the query. Defaults to plain
   *   UNION.
   * @return SelectQueryInterface
   *   The called object.
   */
  public function union(SelectQueryInterface $query, $type = '');

  /**
   * Groups the result set by the specified field.
   *
   * @param $field
   *   The field on which to group. This should be the field as aliased.
   * @return SelectQueryInterface
   *   The called object.
   */
  public function groupBy($field);

  /**
   * Get the equivalent COUNT query of this query as a new query object.
   *
   * @return SelectQueryInterface
   *   A new SelectQuery object with no fields or expressions besides COUNT(*).
   */
  public function countQuery();

  /**
   * Indicates if preExecute() has already been called on that object.
   *
   * @return
   *   TRUE is this query has already been prepared, FALSE otherwise.
   */
  public function isPrepared();

  /**
   * Generic preparation and validation for a SELECT query.
   *
   * @return
   *   TRUE if the validation was successful, FALSE if not.
   */
  public function preExecute(SelectQueryInterface $query = NULL);

  /**
   * Helper function to build most common HAVING conditional clauses.
   *
   * This method can take a variable number of parameters. If called with two
   * parameters, they are taken as $field and $value with $operator having a value
   * of IN if $value is an array and = otherwise.
   *
   * @param $field
   *   The name of the field to check. If you would like to add a more complex
   *   condition involving operators or functions, use having().
   * @param $value
   *   The value to test the field against. In most cases, this is a scalar. For more
   *   complex options, it is an array. The meaning of each element in the array is
   *   dependent on the $operator.
   * @param $operator
   *   The comparison operator, such as =, <, or >=. It also accepts more complex
   *   options such as IN, LIKE, or BETWEEN. Defaults to IN if $value is an array
   *   = otherwise.
   * @return QueryConditionInterface
   *   The called object.
   */
  public function havingCondition($field, $value = NULL, $operator = NULL);

  /**
   * Clone magic method.
   *
   * Select queries have dependent objects that must be deep-cloned.  The
   * connection object itself, however, should not be cloned as that would
   * duplicate the connection itself.
   */
  public function __clone();

  /**
   * Add FOR UPDATE to the query.
   *
   * FOR UPDATE prevents the rows retrieved by the SELECT statement from being
   * modified or deleted by other transactions until the current transaction
   * ends. Other transactions that attempt UPDATE, DELETE, or SELECT FOR UPDATE
   * of these rows will be blocked until the current transaction ends.
   *
   * @param $set
   *   IF TRUE, FOR UPDATE will be added to the query, if FALSE then it won't.
   *
   * @return QueryConditionInterface
   *   The called object.
   */
  public function forUpdate($set = TRUE);
}

/**
 * The base extender class for Select queries.
 */
class SelectQueryExtender implements SelectQueryInterface {

  /**
   * The SelectQuery object we are extending/decorating.
   *
   * @var SelectQueryInterface
   */
  protected $query;

  /**
   * The connection object on which to run this query.
   *
   * @var DatabaseConnection
   */
  protected $connection;

  /**
   * The placeholder counter.
   */
  protected $placeholder = 0;

  public function __construct(SelectQueryInterface $query, DatabaseConnection $connection) {
    $this->query = $query;
    $this->connection = $connection;
  }

  /* Implementations of QueryPlaceholderInterface. */

  public function nextPlaceholder() {
    return $this->placeholder++;
  }

  /* Implementations of QueryAlterableInterface. */

  public function addTag($tag) {
    $this->query->addTag($tag);
    return $this;
  }

  public function hasTag($tag) {
    return $this->query->hasTag($tag);
  }

  public function hasAllTags() {
    return call_user_func_array(array($this->query, 'hasAllTags'), func_get_args());
  }

  public function hasAnyTag() {
    return call_user_func_array(array($this->query, 'hasAnyTags'), func_get_args());
  }

  public function addMetaData($key, $object) {
    $this->query->addMetaData($key, $object);
    return $this;
  }

  public function getMetaData($key) {
    return $this->query->getMetaData($key);
  }

  /* Implementations of QueryConditionInterface for the WHERE clause. */

  public function condition($field, $value = NULL, $operator = NULL) {
    $this->query->condition($field, $value, $operator);
    return $this;
  }

  public function &conditions() {
    return $this->query->conditions();
  }

  public function arguments() {
    return $this->query->arguments();
  }

  public function where($snippet, $args = array()) {
    $this->query->where($snippet, $args);
    return $this;
  }

  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder = NULL) {
    return $this->condition->compile($connection, isset($queryPlaceholder) ? $queryPlaceholder : $this);
  }

  /* Implementations of QueryConditionInterface for the HAVING clause. */

  public function havingCondition($field, $value = NULL, $operator = '=') {
    $this->query->condition($field, $value, $operator, $num_args);
    return $this;
  }

  public function &havingConditions() {
    return $this->having->conditions();
  }

  public function havingArguments() {
    return $this->having->arguments();
  }

  public function having($snippet, $args = array()) {
    $this->query->having($snippet, $args);
    return $this;
  }

  public function havingCompile(DatabaseConnection $connection) {
    return $this->query->havingCompile($connection);
  }

  /* Implementations of QueryExtendableInterface. */

  public function extend($extender_name) {
    // The extender can be anywhere so this needs to go to the registry, which
    // is surely loaded by now.
    $class = $this->connection->getDriverClass($extender_name, array(), TRUE);
    return new $class($this, $this->connection);
  }

  /* Alter accessors to expose the query data to alter hooks. */

  public function &getFields() {
    return $this->query->getFields();
  }

  public function &getExpressions() {
    return $this->query->getExpressions();
  }

  public function &getOrderBy() {
    return $this->query->getOrderBy();
  }

  public function &getGroupBy() {
    return $this->query->getGroupBy();
  }

  public function &getTables() {
    return $this->query->getTables();
  }

  public function &getUnion() {
    return $this->query->getUnion();
  }

  public function getArguments(QueryPlaceholderInterface $queryPlaceholder = NULL) {
    return $this->query->getArguments($queryPlaceholder);
  }

  public function isPrepared() {
    return $this->query->isPrepared();
  }

  public function preExecute(SelectQueryInterface $query = NULL) {
    // If no query object is passed in, use $this.
    if (!isset($query)) {
      $query = $this;
    }

    return $this->query->preExecute($query);
  }

  public function execute() {
    // By calling preExecute() here, we force it to preprocess the extender
    // object rather than just the base query object.  That means
    // hook_query_alter() gets access to the extended object.
    if (!$this->preExecute($this)) {
      return NULL;
    }

    return $this->query->execute();
  }

  public function distinct($distinct = TRUE) {
    $this->query->distinct($distinct);
    return $this;
  }

  public function addField($table_alias, $field, $alias = NULL) {
    return $this->query->addField($table_alias, $field, $alias);
  }

  public function fields($table_alias, array $fields = array()) {
    $this->query->fields($table_alias, $fields);
    return $this;
  }

  public function addExpression($expression, $alias = NULL, $arguments = array()) {
    return $this->query->addExpression($expression, $alias, $arguments);
  }

  public function join($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->query->join($table, $alias, $condition, $arguments);
  }

  public function innerJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->query->innerJoin($table, $alias, $condition, $arguments);
  }

  public function leftJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->query->leftJoin($table, $alias, $condition, $arguments);
  }

  public function rightJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->query->rightJoin($table, $alias, $condition, $arguments);
  }

  public function addJoin($type, $table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->query->addJoin($type, $table, $alias, $condition, $arguments);
  }

  public function orderBy($field, $direction = 'ASC') {
    $this->query->orderBy($field, $direction);
    return $this;
  }

  public function orderRandom() {
    $this->query->orderRandom();
    return $this;
  }

  public function range($start = NULL, $length = NULL) {
    $this->query->range($start, $length);
    return $this;
  }

  public function union(SelectQueryInterface $query, $type = '') {
    $this->query->union($query, $type);
    return $this;
  }

  public function groupBy($field) {
    $this->query->groupBy($field);
    return $this;
  }

  public function forUpdate($set = TRUE) {
    $this->query->forUpdate($set);
    return $this;
  }

  public function countQuery() {
    // Create our new query object that we will mutate into a count query.
    $count = clone($this);

    // Zero-out existing fields and expressions.
    $fields =& $count->getFields();
    $fields = array();
    $expressions =& $count->getExpressions();
    $expressions = array();

    // Also remove 'all_fields' statements, which are expanded into tablename.*
    // when the query is executed.
    $tables = &$count->getTables();
    foreach ($tables as $alias => &$table) {
      unset($table['all_fields']);
    }

    // Ordering a count query is a waste of cycles, and breaks on some
    // databases anyway.
    $orders = &$count->getOrderBy();
    $orders = array();

    // COUNT() is an expression, so we add that back in.
    $count->addExpression('COUNT(*)');

    return $count;
  }

  function isNull($field) {
    $this->query->isNull($field);
    return $this;
  }

  function isNotNull($field) {
    $this->query->isNotNull($field);
    return $this;
  }

  public function exists(SelectQueryInterface $select) {
    $this->query->exists($select);
    return $this;
  }

  public function notExists(SelectQueryInterface $select) {
    $this->query->notExists($select);
    return $this;
  }
  
  public function __toString() {
    return (string) $this->query;
  }

  public function __clone() {
    // We need to deep-clone the query we're wrapping, which in turn may
    // deep-clone other objects.  Exciting!
    $this->query = clone($this->query);
  }

  /**
   * Magic override for undefined methods.
   *
   * If one extender extends another extender, then methods in the inner extender
   * will not be exposed on the outer extender.  That's because we cannot know
   * in advance what those methods will be, so we cannot provide wrapping
   * implementations as we do above.  Instead, we use this slower catch-all method
   * to handle any additional methods.
   */
  public function __call($method, $args) {
    $return = call_user_func_array(array($this->query, $method), $args);

    // Some methods will return the called object as part of a fluent interface.
    // Others will return some useful value.  If it's a value, then the caller
    // probably wants that value.  If it's the called object, then we instead
    // return this object.  That way we don't "lose" an extender layer when
    // chaining methods together.
    if ($return instanceof SelectQueryInterface) {
      return $this;
    }
    else {
      return $return;
    }
  }
}

/**
 * Query builder for SELECT statements.
 */
class SelectQuery extends Query implements SelectQueryInterface {

  /**
   * The fields to SELECT.
   *
   * @var array
   */
  protected $fields = array();

  /**
   * The expressions to SELECT as virtual fields.
   *
   * @var array
   */
  protected $expressions = array();

  /**
   * The tables against which to JOIN.
   *
   * This property is a nested array. Each entry is an array representing
   * a single table against which to join. The structure of each entry is:
   *
   * array(
   *   'type' => $join_type (one of INNER, LEFT OUTER, RIGHT OUTER),
   *   'table' => $table,
   *   'alias' => $alias_of_the_table,
   *   'condition' => $condition_clause_on_which_to_join,
   *   'arguments' => $array_of_arguments_for_placeholders_in_the condition.
   *   'all_fields' => TRUE to SELECT $alias.*, FALSE or NULL otherwise.
   * )
   *
   * If $table is a string, it is taken as the name of a table. If it is
   * a SelectQuery object, it is taken as a subquery.
   *
   * @var array
   */
  protected $tables = array();

  /**
   * The fields by which to order this query.
   *
   * This is an associative array. The keys are the fields to order, and the value
   * is the direction to order, either ASC or DESC.
   *
   * @var array
   */
  protected $order = array();

  /**
   * The fields by which to group.
   *
   * @var array
   */
  protected $group = array();

  /**
   * The conditional object for the WHERE clause.
   *
   * @var DatabaseCondition
   */
  protected $where;

  /**
   * The conditional object for the HAVING clause.
   *
   * @var DatabaseCondition
   */
  protected $having;

  /**
   * Whether or not this query should be DISTINCT
   *
   * @var boolean
   */
  protected $distinct = FALSE;

  /**
   * The range limiters for this query.
   *
   * @var array
   */
  protected $range;

  /**
   * An array whose elements specify a query to UNION, and the UNION type. The
   * 'type' key may be '', 'ALL', or 'DISTINCT' to represent a 'UNION',
   * 'UNION ALL', or 'UNION DISTINCT' statement, respectively.
   *
   * All entries in this array will be applied from front to back, with the
   * first query to union on the right of the original query, the second union
   * to the right of the first, etc.
   *
   * @var array
   */
  protected $union = array();

  /**
   * Indicates if preExecute() has already been called.
   * @var boolean
   */
  protected $prepared = FALSE;

  /**
   * The FOR UPDATE status
   */
  protected $forUpdate = FALSE;

  public function __construct($table, $alias = NULL, DatabaseConnection $connection, $options = array()) {
    $options['return'] = Database::RETURN_STATEMENT;
    parent::__construct($connection, $options);
    $this->where = new DatabaseCondition('AND');
    $this->having = new DatabaseCondition('AND');
    $this->addJoin(NULL, $table, $alias);
  }

  /* Implementations of QueryAlterableInterface. */

  public function addTag($tag) {
    $this->alterTags[$tag] = 1;
    return $this;
  }

  public function hasTag($tag) {
    return isset($this->alterTags[$tag]);
  }

  public function hasAllTags() {
    return !(boolean)array_diff(func_get_args(), array_keys($this->alterTags));
  }

  public function hasAnyTag() {
    return (boolean)array_intersect(func_get_args(), array_keys($this->alterTags));
  }

  public function addMetaData($key, $object) {
    $this->alterMetaData[$key] = $object;
    return $this;
  }

  public function getMetaData($key) {
    return isset($this->alterMetaData[$key]) ? $this->alterMetaData[$key] : NULL;
  }

  /* Implementations of QueryConditionInterface for the WHERE clause. */

  public function condition($field, $value = NULL, $operator = NULL) {
    $this->where->condition($field, $value, $operator);
    return $this;
  }

  public function &conditions() {
    return $this->where->conditions();
  }

  public function arguments() {
    return $this->where->arguments();
  }

  public function where($snippet, $args = array()) {
    $this->where->where($snippet, $args);
    return $this;
  }

  public function isNull($field) {
    $this->where->isNull($field);
    return $this;
  }

  public function isNotNull($field) {
    $this->where->isNotNull($field);
    return $this;
  }

  public function exists(SelectQueryInterface $select) {
    $this->where->exists($select);
    return $this;
  }

  public function notExists(SelectQueryInterface $select) {
    $this->where->notExists($select);
    return $this;
  }
  
  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder = NULL) {
    return $this->where->compile($connection, isset($queryPlaceholder) ? $queryPlaceholder : $this);
  }

  /* Implementations of QueryConditionInterface for the HAVING clause. */

  public function havingCondition($field, $value = NULL, $operator = NULL) {
    $this->having->condition($field, $value, $operator);
    return $this;
  }

  public function &havingConditions() {
    return $this->having->conditions();
  }

  public function havingArguments() {
    return $this->having->arguments();
  }

  public function having($snippet, $args = array()) {
    $this->having->where($snippet, $args);
    return $this;
  }

  public function havingCompile(DatabaseConnection $connection) {
    return $this->having->compile($connection, $this);
  }

  /* Implementations of QueryExtendableInterface. */

  public function extend($extender_name) {
    $override_class = $extender_name . '_' . $this->connection->driver();
    if (class_exists($override_class)) {
      $extender_name = $override_class;
    }
    return new $extender_name($this, $this->connection);
  }

  public function havingIsNull($field) {
    $this->having->isNull($field);
    return $this;
  }

  public function havingIsNotNull($field) {
    $this->having->isNotNull($field);
    return $this;
  }
  
  public function havingExists(SelectQueryInterface $select) {
    $this->having->exists($select);
    return $this;
  }
  
  public function havingNotExists(SelectQueryInterface $select) {
    $this->having->notExists($select);
    return $this;
  }
  
  public function forUpdate($set = TRUE) {
    if (isset($set)) {
      $this->forUpdate = $set;
    }
    return $this;
  }

  /* Alter accessors to expose the query data to alter hooks. */

  public function &getFields() {
    return $this->fields;
  }

  public function &getExpressions() {
    return $this->expressions;
  }

  public function &getOrderBy() {
    return $this->order;
  }

  public function &getGroupBy() {
    return $this->group;
  }

  public function &getTables() {
    return $this->tables;
  }

  public function &getUnion() {
    return $this->union;
  }

  public function getArguments(QueryPlaceholderInterface $queryPlaceholder = NULL) {
    if (!isset($queryPlaceholder)) {
      $queryPlaceholder = $this;
    }
    $this->where->compile($this->connection, $queryPlaceholder);
    $this->having->compile($this->connection, $queryPlaceholder);
    $args = $this->where->arguments() + $this->having->arguments();

    foreach ($this->tables as $table) {
      if ($table['arguments']) {
        $args += $table['arguments'];
      }
      // If this table is a subquery, grab its arguments recursively.
      if ($table['table'] instanceof SelectQueryInterface) {
        $args += $table['table']->getArguments($queryPlaceholder);
      }
    }

    foreach ($this->expressions as $expression) {
      if ($expression['arguments']) {
        $args += $expression['arguments'];
      }
    }

    // If there are any dependent queries to UNION,
    // incorporate their arguments recursively.
    foreach ($this->union as $union) {
      $args += $union['query']->getArguments($queryPlaceholder);
    }

    return $args;
  }

  /**
   * Indicates if preExecute() has already been called on that object.
   */
  public function isPrepared() {
    return $this->prepared;
  }

  /**
   * Generic preparation and validation for a SELECT query.
   *
   * @return
   *   TRUE if the validation was successful, FALSE if not.
   */
  public function preExecute(SelectQueryInterface $query = NULL) {
    // If no query object is passed in, use $this.
    if (!isset($query)) {
      $query = $this;
    }

    // Only execute this once.
    if ($query->isPrepared()) {
      return TRUE;
    }

    // Modules may alter all queries or only those having a particular tag.
    if (isset($this->alterTags)) {
      $hooks = array('query');
      foreach ($this->alterTags as $tag => $value) {
        $hooks[] = 'query_' . $tag;
      }
      drupal_alter($hooks, $query);
    }

    $this->prepared = TRUE;

    // Now also prepare any sub-queries.
    foreach ($this->tables as $table) {
      if ($table['table'] instanceof SelectQueryInterface) {
        $table['table']->preExecute();
      }
    }

    foreach ($this->union as $union) {
      $union['query']->preExecute();
    }

    return $this->prepared;
  }

  public function execute() {
    // If validation fails, simply return NULL.
    // Note that validation routines in preExecute() may throw exceptions instead.
    if (!$this->preExecute()) {
      return NULL;
    }

    $args = $this->getArguments();
    return $this->connection->query((string) $this, $args, $this->queryOptions);
  }

  public function distinct($distinct = TRUE) {
    $this->distinct = $distinct;
    return $this;
  }

  public function addField($table_alias, $field, $alias = NULL) {
    // If no alias is specified, first try the field name itself.
    if (empty($alias)) {
      $alias = $field;
    }

    // If that's already in use, try the table name and field name.
    if (!empty($this->fields[$alias])) {
      $alias = $table_alias . '_' . $field;
    }

    // If that is already used, just add a counter until we find an unused alias.
    $alias_candidate = $alias;
    $count = 2;
    while (!empty($this->fields[$alias_candidate])) {
      $alias_candidate = $alias . '_' . $count++;
    }
    $alias = $alias_candidate;

    $this->fields[$alias] = array(
      'field' => $field,
      'table' => $table_alias,
      'alias' => $alias,
    );

    return $alias;
  }

  public function fields($table_alias, array $fields = array()) {

    if ($fields) {
      foreach ($fields as $field) {
        // We don't care what alias was assigned.
        $this->addField($table_alias, $field);
      }
    }
    else {
      // We want all fields from this table.
      $this->tables[$table_alias]['all_fields'] = TRUE;
    }

    return $this;
  }

  public function addExpression($expression, $alias = NULL, $arguments = array()) {
    if (empty($alias)) {
      $alias = 'expression';
    }

    $alias_candidate = $alias;
    $count = 2;
    while (!empty($this->expressions[$alias_candidate])) {
      $alias_candidate = $alias . '_' . $count++;
    }
    $alias = $alias_candidate;

    $this->expressions[$alias] = array(
      'expression' => $expression,
      'alias' => $alias,
      'arguments' => $arguments,
    );

    return $alias;
  }

  public function join($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->addJoin('INNER', $table, $alias, $condition, $arguments);
  }

  public function innerJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->addJoin('INNER', $table, $alias, $condition, $arguments);
  }

  public function leftJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->addJoin('LEFT OUTER', $table, $alias, $condition, $arguments);
  }

  public function rightJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
    return $this->addJoin('RIGHT OUTER', $table, $alias, $condition, $arguments);
  }

  public function addJoin($type, $table, $alias = NULL, $condition = NULL, $arguments = array()) {

    if (empty($alias)) {
      if ($table instanceof SelectQueryInterface) {
        $alias = 'subquery';
      }
      else {
        $alias = $table;
      }
    }

    $alias_candidate = $alias;
    $count = 2;
    while (!empty($this->tables[$alias_candidate])) {
      $alias_candidate = $alias . '_' . $count++;
    }
    $alias = $alias_candidate;

    if (is_string($condition)) {
      $condition = str_replace('%alias', $alias, $condition);
    }

    $this->tables[$alias] = array(
      'join type' => $type,
      'table' => $table,
      'alias' => $alias,
      'condition' => $condition,
      'arguments' => $arguments,
    );

    return $alias;
  }

  public function orderBy($field, $direction = 'ASC') {
    $this->order[$field] = $direction;
    return $this;
  }

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

  public function range($start = NULL, $length = NULL) {
    $this->range = func_num_args() ? array('start' => $start, 'length' => $length) : array();
    return $this;
  }

  public function union(SelectQueryInterface $query, $type = '') {
    // Handle UNION aliasing.
    switch ($type) {
      // Fold UNION DISTINCT to UNION for better cross database support.
      case 'DISTINCT':
      case '':
        $type = 'UNION';
        break;

      case 'ALL':
        $type = 'UNION ALL';
      default:
    }

    $this->union[] = array(
      'type' => $type,
      'query' => $query,
    );

    return $this;
  }

  public function groupBy($field) {
    $this->group[$field] = $field;
    return $this;
  }

  public function countQuery() {
    // Create our new query object that we will mutate into a count query.
    $count = clone($this);

    $group_by = $count->getGroupBy();

    if (!$count->distinct) {
      // When not executing a distinct query, we can zero-out existing fields
      // and expressions that are not used by a GROUP BY.  Fields listed in
      // the GROUP BY clause need to be present in the query.
      $fields =& $count->getFields();
      foreach (array_keys($fields) as $field) {
        if (empty($group_by[$field])) {
          unset($fields[$field]);
        }
      }
      $expressions =& $count->getExpressions();
      foreach (array_keys($expressions) as $field) {
        if (empty($group_by[$field])) {
          unset($expressions[$field]);
        }
      }

      // Also remove 'all_fields' statements, which are expanded into tablename.*
      // when the query is executed.
      foreach ($count->tables as $alias => &$table) {
        unset($table['all_fields']);
      }
    }

    // If we've just removed all fields from the query, make sure there is at
    // least one so that the query still runs.
    $count->addExpression('1');

    // Ordering a count query is a waste of cycles, and breaks on some
    // databases anyway.
    $orders = &$count->getOrderBy();
    $orders = array();

    if ($count->distinct && !empty($group_by)) {
      // If the query is distinct and contains a GROUP BY, we need to remove the
      // distinct because SQL99 does not support counting on distinct multiple fields.
      $count->distinct = FALSE;
    }

    $query = $this->connection->select($count);
    $query->addExpression('COUNT(*)');

    return $query;
  }

  public function __toString() {

    // Create a comments string to prepend to the query.
    $comments = (!empty($this->comments)) ? '/* ' . implode('; ', $this->comments) . ' */ ' : '';

    // SELECT
    $query = $comments . 'SELECT ';
    if ($this->distinct) {
      $query .= 'DISTINCT ';
    }

    // FIELDS and EXPRESSIONS
    $fields = array();
    foreach ($this->tables as $alias => $table) {
      if (!empty($table['all_fields'])) {
        $fields[] = $this->connection->escapeTable($alias) . '.*';
      }
    }
    foreach ($this->fields as $alias => $field) {
      // Always use the AS keyword for field aliases, as some
      // databases require it (e.g., PostgreSQL).
      $fields[] = (isset($field['table']) ? $this->connection->escapeTable($field['table']) . '.' : '') . $this->connection->escapeField($field['field']) . ' AS ' . $this->connection->escapeAlias($field['alias']);
    }
    foreach ($this->expressions as $alias => $expression) {
      $fields[] = $expression['expression'] . ' AS ' . $this->connection->escapeAlias($expression['alias']);
    }
    $query .= implode(', ', $fields);


    // FROM - We presume all queries have a FROM, as any query that doesn't won't need the query builder anyway.
    $query .= "\nFROM ";
    foreach ($this->tables as $alias => $table) {
      $query .= "\n";
      if (isset($table['join type'])) {
        $query .= $table['join type'] . ' JOIN ';
      }

      // If the table is a subquery, compile it and integrate it into this query.
      if ($table['table'] instanceof SelectQueryInterface) {
        // Run preparation steps on this sub-query before converting to string.
        $subquery = $table['table'];
        $subquery->preExecute();
        $table_string = '(' . (string) $subquery . ')';
      }
      else {
        $table_string = '{' . $this->connection->escapeTable($table['table']) . '}';
      }

      // Don't use the AS keyword for table aliases, as some
      // databases don't support it (e.g., Oracle).
      $query .=  $table_string . ' ' . $this->connection->escapeTable($table['alias']);

      if (!empty($table['condition'])) {
        $query .= ' ON ' . $table['condition'];
      }
    }

    // WHERE
    if (count($this->where)) {
      // The following line will not generate placeholders correctly if there
      // is a subquery. Fortunately, it is also called from getArguments() first
      // so it's not a problem in practice... unless you try to call __toString()
      // before calling getArguments().  That is a problem that we will have to
      // fix in Drupal 8, because it requires more refactoring than we are
      // able to do in Drupal 7.
      // @todo Move away from __toString() For SelectQuery compilation at least.
      $this->where->compile($this->connection, $this);
      // There is an implicit string cast on $this->condition.
      $query .= "\nWHERE " . $this->where;
    }

    // GROUP BY
    if ($this->group) {
      $query .= "\nGROUP BY " . implode(', ', $this->group);
    }

    // HAVING
    if (count($this->having)) {
      $this->having->compile($this->connection, $this);
      // There is an implicit string cast on $this->having.
      $query .= "\nHAVING " . $this->having;
    }

    // ORDER BY
    if ($this->order) {
      $query .= "\nORDER BY ";
      $fields = array();
      foreach ($this->order as $field => $direction) {
        $fields[] = $field . ' ' . $direction;
      }
      $query .= implode(', ', $fields);
    }

    // RANGE
    // There is no universal SQL standard for handling range or limit clauses.
    // Fortunately, all core-supported databases use the same range syntax.
    // Databases that need a different syntax can override this method and
    // do whatever alternate logic they need to.
    if (!empty($this->range)) {
      $query .= "\nLIMIT " . (int) $this->range['length'] . " OFFSET " . (int) $this->range['start'];
    }

    // UNION is a little odd, as the select queries to combine are passed into
    // this query, but syntactically they all end up on the same level.
    if ($this->union) {
      foreach ($this->union as $union) {
        $query .= ' ' . $union['type'] . ' ' . (string) $union['query'];
      }
    }

    if ($this->forUpdate) {
      $query .= ' FOR UPDATE';
    }

    return $query;
  }

  public function __clone() {
    // On cloning, also clone the dependent objects. However, we do not
    // want to clone the database connection object as that would duplicate the
    // connection itself.

    $this->where = clone($this->where);
    $this->having = clone($this->having);
    foreach ($this->union as $key => $aggregate) {
      $this->union[$key]['query'] = clone($aggregate['query']);
    }
  }
}

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

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