cms/drupal/includes/database/query.inc
changeset 541 e756a8c72c3d
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cms/drupal/includes/database/query.inc	Fri Sep 08 12:04:06 2017 +0200
@@ -0,0 +1,1963 @@
+<?php
+
+/**
+ * @addtogroup database
+ * @{
+ */
+
+/**
+ * @file
+ * Non-specific Database query code. Used by all engines.
+ */
+
+/**
+ * Interface for a conditional clause in a query.
+ */
+interface QueryConditionInterface {
+
+  /**
+   * Helper function: builds the most common 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.
+   *
+   * Do not use this method to test for NULL values. Instead, use
+   * QueryConditionInterface::isNull() or QueryConditionInterface::isNotNull().
+   *
+   * @param $field
+   *   The name of the field to check. If you would like to add a more complex
+   *   condition involving operators or functions, use where().
+   * @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 $value is
+   *   an array, and = otherwise.
+   *
+   * @return QueryConditionInterface
+   *   The called object.
+   *
+   * @see QueryConditionInterface::isNull()
+   * @see QueryConditionInterface::isNotNull()
+   */
+  public function condition($field, $value = NULL, $operator = NULL);
+
+  /**
+   * Adds an arbitrary WHERE clause to the query.
+   *
+   * @param $snippet
+   *   A portion of a WHERE clause as a prepared statement. It must use named
+   *   placeholders, not ? placeholders.
+   * @param $args
+   *   An associative array of arguments.
+   *
+   * @return QueryConditionInterface
+   *   The called object.
+   */
+  public function where($snippet, $args = array());
+
+  /**
+   * Sets a condition that the specified field be NULL.
+   *
+   * @param $field
+   *   The name of the field to check.
+   *
+   * @return QueryConditionInterface
+   *   The called object.
+   */
+  public function isNull($field);
+
+  /**
+   * Sets a condition that the specified field be NOT NULL.
+   *
+   * @param $field
+   *   The name of the field to check.
+   *
+   * @return QueryConditionInterface
+   *   The called object.
+   */
+  public function isNotNull($field);
+
+  /**
+   * Sets a condition that the specified subquery returns values.
+   *
+   * @param SelectQueryInterface $select
+   *   The subquery that must contain results.
+   *
+   * @return QueryConditionInterface
+   *   The called object.
+   */
+  public function exists(SelectQueryInterface $select);
+
+  /**
+   * Sets a condition that the specified subquery returns no values.
+   *
+   * @param SelectQueryInterface $select
+   *   The subquery that must not contain results.
+   *
+   * @return QueryConditionInterface
+   *   The called object.
+   */
+  public function notExists(SelectQueryInterface $select);
+
+  /**
+   * Gets a complete list of all conditions in this conditional clause.
+   *
+   * This method returns by reference. That allows alter hooks to access the
+   * data structure directly and manipulate it before it gets compiled.
+   *
+   * The data structure that is returned is an indexed array of entries, where
+   * each entry looks like the following:
+   * @code
+   * array(
+   *   'field' => $field,
+   *   'value' => $value,
+   *   'operator' => $operator,
+   * );
+   * @endcode
+   *
+   * In the special case that $operator is NULL, the $field is taken as a raw
+   * SQL snippet (possibly containing a function) and $value is an associative
+   * array of placeholders for the snippet.
+   *
+   * There will also be a single array entry of #conjunction, which is the
+   * conjunction that will be applied to the array, such as AND.
+   */
+  public function &conditions();
+
+  /**
+   * Gets a complete list of all values to insert into the prepared statement.
+   *
+   * @return
+   *   An associative array of placeholders and values.
+   */
+  public function arguments();
+
+  /**
+   * Compiles the saved conditions for later retrieval.
+   *
+   * This method does not return anything, but simply prepares data to be
+   * retrieved via __toString() and arguments().
+   *
+   * @param $connection
+   *   The database connection for which to compile the conditionals.
+   * @param $queryPlaceholder
+   *   The query this condition belongs to. If not given, the current query is
+   *   used.
+   */
+  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder);
+
+  /**
+   * Check whether a condition has been previously compiled.
+   *
+   * @return
+   *   TRUE if the condition has been previously compiled.
+   */
+  public function compiled();
+}
+
+
+/**
+ * Interface for a query that can be manipulated via an alter hook.
+ */
+interface QueryAlterableInterface {
+
+  /**
+   * Adds a tag to a query.
+   *
+   * Tags are strings that identify a query. A query may have any number of
+   * tags. Tags are used to mark a query so that alter hooks may decide if they
+   * wish to take action. Tags should be all lower-case and contain only
+   * letters, numbers, and underscore, and start with a letter. That is, they
+   * should follow the same rules as PHP identifiers in general.
+   *
+   * @param $tag
+   *   The tag to add.
+   *
+   * @return QueryAlterableInterface
+   *   The called object.
+   */
+  public function addTag($tag);
+
+  /**
+   * Determines if a given query has a given tag.
+   *
+   * @param $tag
+   *   The tag to check.
+   *
+   * @return
+   *   TRUE if this query has been marked with this tag, FALSE otherwise.
+   */
+  public function hasTag($tag);
+
+  /**
+   * Determines if a given query has all specified tags.
+   *
+   * @param $tags
+   *   A variable number of arguments, one for each tag to check.
+   *
+   * @return
+   *   TRUE if this query has been marked with all specified tags, FALSE
+   *   otherwise.
+   */
+  public function hasAllTags();
+
+  /**
+   * Determines if a given query has any specified tag.
+   *
+   * @param $tags
+   *   A variable number of arguments, one for each tag to check.
+   *
+   * @return
+   *   TRUE if this query has been marked with at least one of the specified
+   *   tags, FALSE otherwise.
+   */
+  public function hasAnyTag();
+
+  /**
+   * Adds additional metadata to the query.
+   *
+   * Often, a query may need to provide additional contextual data to alter
+   * hooks. Alter hooks may then use that information to decide if and how
+   * to take action.
+   *
+   * @param $key
+   *   The unique identifier for this piece of metadata. Must be a string that
+   *   follows the same rules as any other PHP identifier.
+   * @param $object
+   *   The additional data to add to the query. May be any valid PHP variable.
+   *
+   * @return QueryAlterableInterface
+   *   The called object.
+   */
+  public function addMetaData($key, $object);
+
+  /**
+   * Retrieves a given piece of metadata.
+   *
+   * @param $key
+   *   The unique identifier for the piece of metadata to retrieve.
+   *
+   * @return
+   *   The previously attached metadata object, or NULL if one doesn't exist.
+   */
+  public function getMetaData($key);
+}
+
+/**
+ * Interface for a query that accepts placeholders.
+ */
+interface QueryPlaceholderInterface {
+
+  /**
+   * Returns a unique identifier for this object.
+   */
+  public function uniqueIdentifier();
+
+  /**
+   * Returns the next placeholder ID for the query.
+   *
+   * @return
+   *   The next available placeholder ID as an integer.
+   */
+  public function nextPlaceholder();
+}
+
+/**
+ * Base class for query builders.
+ *
+ * Note that query builders use PHP's magic __toString() method to compile the
+ * query object into a prepared statement.
+ */
+abstract class Query implements QueryPlaceholderInterface {
+
+  /**
+   * The connection object on which to run this query.
+   *
+   * @var DatabaseConnection
+   */
+  protected $connection;
+
+  /**
+   * The target of the connection object.
+   *
+   * @var string
+   */
+  protected $connectionTarget;
+
+  /**
+   * The key of the connection object.
+   *
+   * @var string
+   */
+  protected $connectionKey;
+
+  /**
+   * The query options to pass on to the connection object.
+   *
+   * @var array
+   */
+  protected $queryOptions;
+
+  /**
+   * A unique identifier for this query object.
+   */
+  protected $uniqueIdentifier;
+
+  /**
+   * The placeholder counter.
+   */
+  protected $nextPlaceholder = 0;
+
+  /**
+   * An array of comments that can be prepended to a query.
+   *
+   * @var array
+   */
+  protected $comments = array();
+
+  /**
+   * Constructs a Query object.
+   *
+   * @param DatabaseConnection $connection
+   *   Database connection object.
+   * @param array $options
+   *   Array of query options.
+   */
+  public function __construct(DatabaseConnection $connection, $options) {
+    $this->uniqueIdentifier = uniqid('', TRUE);
+
+    $this->connection = $connection;
+    $this->connectionKey = $this->connection->getKey();
+    $this->connectionTarget = $this->connection->getTarget();
+
+    $this->queryOptions = $options;
+  }
+
+  /**
+   * Implements the magic __sleep function to disconnect from the database.
+   */
+  public function __sleep() {
+    $keys = get_object_vars($this);
+    unset($keys['connection']);
+    return array_keys($keys);
+  }
+
+  /**
+   * Implements the magic __wakeup function to reconnect to the database.
+   */
+  public function __wakeup() {
+    $this->connection = Database::getConnection($this->connectionTarget, $this->connectionKey);
+  }
+
+  /**
+   * Implements the magic __clone function.
+   */
+  public function __clone() {
+    $this->uniqueIdentifier = uniqid('', TRUE);
+  }
+
+  /**
+   * Runs the query against the database.
+   */
+  abstract protected function execute();
+
+  /**
+   * Implements PHP magic __toString method to convert the query to a string.
+   *
+   * The toString operation is how we compile a query object to a prepared
+   * statement.
+   *
+   * @return
+   *   A prepared statement query string for this object.
+   */
+  abstract public function __toString();
+
+  /**
+   * Returns a unique identifier for this object.
+   */
+  public function uniqueIdentifier() {
+    return $this->uniqueIdentifier;
+  }
+
+  /**
+   * Gets the next placeholder value for this query object.
+   *
+   * @return int
+   *   Next placeholder value.
+   */
+  public function nextPlaceholder() {
+    return $this->nextPlaceholder++;
+  }
+
+  /**
+   * Adds a comment to the query.
+   *
+   * By adding a comment to a query, you can more easily find it in your
+   * query log or the list of active queries on an SQL server. This allows
+   * for easier debugging and allows you to more easily find where a query
+   * with a performance problem is being generated.
+   *
+   * The comment string will be sanitized to remove * / and other characters
+   * that may terminate the string early so as to avoid SQL injection attacks.
+   *
+   * @param $comment
+   *   The comment string to be inserted into the query.
+   *
+   * @return Query
+   *   The called object.
+   */
+  public function comment($comment) {
+    $this->comments[] = $comment;
+    return $this;
+  }
+
+  /**
+   * Returns a reference to the comments array for the query.
+   *
+   * Because this method returns by reference, alter hooks may edit the comments
+   * array directly to make their changes. If just adding comments, however, the
+   * use of comment() is preferred.
+   *
+   * Note that this method must be called by reference as well:
+   * @code
+   * $comments =& $query->getComments();
+   * @endcode
+   *
+   * @return
+   *   A reference to the comments array structure.
+   */
+  public function &getComments() {
+    return $this->comments;
+  }
+}
+
+/**
+ * General class for an abstracted INSERT query.
+ */
+class InsertQuery extends Query {
+
+  /**
+   * The table on which to insert.
+   *
+   * @var string
+   */
+  protected $table;
+
+  /**
+   * An array of fields on which to insert.
+   *
+   * @var array
+   */
+  protected $insertFields = array();
+
+  /**
+   * An array of fields that should be set to their database-defined defaults.
+   *
+   * @var array
+   */
+  protected $defaultFields = array();
+
+  /**
+   * A nested array of values to insert.
+   *
+   * $insertValues is an array of arrays. Each sub-array is either an
+   * associative array whose keys are field names and whose values are field
+   * values to insert, or a non-associative array of values in the same order
+   * as $insertFields.
+   *
+   * Whether multiple insert sets will be run in a single query or multiple
+   * queries is left to individual drivers to implement in whatever manner is
+   * most appropriate. The order of values in each sub-array must match the
+   * order of fields in $insertFields.
+   *
+   * @var array
+   */
+  protected $insertValues = array();
+
+  /**
+   * A SelectQuery object to fetch the rows that should be inserted.
+   *
+   * @var SelectQueryInterface
+   */
+  protected $fromQuery;
+
+  /**
+   * Constructs an InsertQuery object.
+   *
+   * @param DatabaseConnection $connection
+   *   A DatabaseConnection object.
+   * @param string $table
+   *   Name of the table to associate with this query.
+   * @param array $options
+   *   Array of database options.
+   */
+  public function __construct($connection, $table, array $options = array()) {
+    if (!isset($options['return'])) {
+      $options['return'] = Database::RETURN_INSERT_ID;
+    }
+    parent::__construct($connection, $options);
+    $this->table = $table;
+  }
+
+  /**
+   * Adds a set of field->value pairs to be inserted.
+   *
+   * This method may only be called once. Calling it a second time will be
+   * ignored. To queue up multiple sets of values to be inserted at once,
+   * use the values() method.
+   *
+   * @param $fields
+   *   An array of fields on which to insert. This array may be indexed or
+   *   associative. If indexed, the array is taken to be the list of fields.
+   *   If associative, the keys of the array are taken to be the fields and
+   *   the values are taken to be corresponding values to insert. If a
+   *   $values argument is provided, $fields must be indexed.
+   * @param $values
+   *   An array of fields to insert into the database. The values must be
+   *   specified in the same order as the $fields array.
+   *
+   * @return InsertQuery
+   *   The called object.
+   */
+  public function fields(array $fields, array $values = array()) {
+    if (empty($this->insertFields)) {
+      if (empty($values)) {
+        if (!is_numeric(key($fields))) {
+          $values = array_values($fields);
+          $fields = array_keys($fields);
+        }
+      }
+      $this->insertFields = $fields;
+      if (!empty($values)) {
+        $this->insertValues[] = $values;
+      }
+    }
+
+    return $this;
+  }
+
+  /**
+   * Adds another set of values to the query to be inserted.
+   *
+   * If $values is a numeric-keyed array, it will be assumed to be in the same
+   * order as the original fields() call. If it is associative, it may be
+   * in any order as long as the keys of the array match the names of the
+   * fields.
+   *
+   * @param $values
+   *   An array of values to add to the query.
+   *
+   * @return InsertQuery
+   *   The called object.
+   */
+  public function values(array $values) {
+    if (is_numeric(key($values))) {
+      $this->insertValues[] = $values;
+    }
+    else {
+      // Reorder the submitted values to match the fields array.
+      foreach ($this->insertFields as $key) {
+        $insert_values[$key] = $values[$key];
+      }
+      // For consistency, the values array is always numerically indexed.
+      $this->insertValues[] = array_values($insert_values);
+    }
+    return $this;
+  }
+
+  /**
+   * Specifies fields for which the database defaults should be used.
+   *
+   * If you want to force a given field to use the database-defined default,
+   * not NULL or undefined, use this method to instruct the database to use
+   * default values explicitly. In most cases this will not be necessary
+   * unless you are inserting a row that is all default values, as you cannot
+   * specify no values in an INSERT query.
+   *
+   * Specifying a field both in fields() and in useDefaults() is an error
+   * and will not execute.
+   *
+   * @param $fields
+   *   An array of values for which to use the default values
+   *   specified in the table definition.
+   *
+   * @return InsertQuery
+   *   The called object.
+   */
+  public function useDefaults(array $fields) {
+    $this->defaultFields = $fields;
+    return $this;
+  }
+
+  /**
+   * Sets the fromQuery on this InsertQuery object.
+   *
+   * @param SelectQueryInterface $query
+   *   The query to fetch the rows that should be inserted.
+   *
+   * @return InsertQuery
+   *   The called object.
+   */
+  public function from(SelectQueryInterface $query) {
+    $this->fromQuery = $query;
+    return $this;
+  }
+
+  /**
+   * Executes the insert query.
+   *
+   * @return
+   *   The last insert ID of the query, if one exists. If the query
+   *   was given multiple sets of values to insert, the return value is
+   *   undefined. If no fields are specified, this method will do nothing and
+   *   return NULL. That makes it safe to use in multi-insert loops.
+   */
+  public function execute() {
+    // If validation fails, simply return NULL. Note that validation routines
+    // in preExecute() may throw exceptions instead.
+    if (!$this->preExecute()) {
+      return NULL;
+    }
+
+    // If we're selecting from a SelectQuery, finish building the query and
+    // pass it back, as any remaining options are irrelevant.
+    if (!empty($this->fromQuery)) {
+      $sql = (string) $this;
+      // The SelectQuery may contain arguments, load and pass them through.
+      return $this->connection->query($sql, $this->fromQuery->getArguments(), $this->queryOptions);
+    }
+
+    $last_insert_id = 0;
+
+    // Each insert happens in its own query in the degenerate case. However,
+    // we wrap it in a transaction so that it is atomic where possible. On many
+    // databases, such as SQLite, this is also a notable performance boost.
+    $transaction = $this->connection->startTransaction();
+
+    try {
+      $sql = (string) $this;
+      foreach ($this->insertValues as $insert_values) {
+        $last_insert_id = $this->connection->query($sql, $insert_values, $this->queryOptions);
+      }
+    }
+    catch (Exception $e) {
+      // One of the INSERTs failed, rollback the whole batch.
+      $transaction->rollback();
+      // Rethrow the exception for the calling code.
+      throw $e;
+    }
+
+    // Re-initialize the values array so that we can re-use this query.
+    $this->insertValues = array();
+
+    // Transaction commits here where $transaction looses scope.
+
+    return $last_insert_id;
+  }
+
+  /**
+   * Implements PHP magic __toString method to convert the query to a string.
+   *
+   * @return string
+   *   The prepared statement.
+   */
+  public function __toString() {
+    // Create a sanitized comment string to prepend to the query.
+    $comments = $this->connection->makeComment($this->comments);
+
+    // Default fields are always placed first for consistency.
+    $insert_fields = array_merge($this->defaultFields, $this->insertFields);
+
+    if (!empty($this->fromQuery)) {
+      return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') ' . $this->fromQuery;
+    }
+
+    // For simplicity, we will use the $placeholders array to inject
+    // default keywords even though they are not, strictly speaking,
+    // placeholders for prepared statements.
+    $placeholders = array();
+    $placeholders = array_pad($placeholders, count($this->defaultFields), 'default');
+    $placeholders = array_pad($placeholders, count($this->insertFields), '?');
+
+    return $comments . 'INSERT INTO {' . $this->table . '} (' . implode(', ', $insert_fields) . ') VALUES (' . implode(', ', $placeholders) . ')';
+  }
+
+  /**
+   * Preprocesses and validates the query.
+   *
+   * @return
+   *   TRUE if the validation was successful, FALSE if not.
+   *
+   * @throws FieldsOverlapException
+   * @throws NoFieldsException
+   */
+  public function preExecute() {
+    // Confirm that the user did not try to specify an identical
+    // field and default field.
+    if (array_intersect($this->insertFields, $this->defaultFields)) {
+      throw new FieldsOverlapException('You may not specify the same field to have a value and a schema-default value.');
+    }
+
+    if (!empty($this->fromQuery)) {
+      // We have to assume that the used aliases match the insert fields.
+      // Regular fields are added to the query before expressions, maintain the
+      // same order for the insert fields.
+      // This behavior can be overridden by calling fields() manually as only the
+      // first call to fields() does have an effect.
+      $this->fields(array_merge(array_keys($this->fromQuery->getFields()), array_keys($this->fromQuery->getExpressions())));
+    }
+    else {
+      // Don't execute query without fields.
+      if (count($this->insertFields) + count($this->defaultFields) == 0) {
+        throw new NoFieldsException('There are no fields available to insert with.');
+      }
+    }
+
+    // If no values have been added, silently ignore this query. This can happen
+    // if values are added conditionally, so we don't want to throw an
+    // exception.
+    if (!isset($this->insertValues[0]) && count($this->insertFields) > 0 && empty($this->fromQuery)) {
+      return FALSE;
+    }
+    return TRUE;
+  }
+}
+
+/**
+ * General class for an abstracted DELETE operation.
+ */
+class DeleteQuery extends Query implements QueryConditionInterface {
+
+  /**
+   * The table from which to delete.
+   *
+   * @var string
+   */
+  protected $table;
+
+  /**
+   * The condition object for this query.
+   *
+   * Condition handling is handled via composition.
+   *
+   * @var DatabaseCondition
+   */
+  protected $condition;
+
+  /**
+   * Constructs a DeleteQuery object.
+   *
+   * @param DatabaseConnection $connection
+   *   A DatabaseConnection object.
+   * @param string $table
+   *   Name of the table to associate with this query.
+   * @param array $options
+   *   Array of database options.
+   */
+  public function __construct(DatabaseConnection $connection, $table, array $options = array()) {
+    $options['return'] = Database::RETURN_AFFECTED;
+    parent::__construct($connection, $options);
+    $this->table = $table;
+
+    $this->condition = new DatabaseCondition('AND');
+  }
+
+  /**
+   * Implements QueryConditionInterface::condition().
+   */
+  public function condition($field, $value = NULL, $operator = NULL) {
+    $this->condition->condition($field, $value, $operator);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNull().
+   */
+  public function isNull($field) {
+    $this->condition->isNull($field);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNotNull().
+   */
+  public function isNotNull($field) {
+    $this->condition->isNotNull($field);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::exists().
+   */
+  public function exists(SelectQueryInterface $select) {
+    $this->condition->exists($select);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::notExists().
+   */
+  public function notExists(SelectQueryInterface $select) {
+    $this->condition->notExists($select);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::conditions().
+   */
+  public function &conditions() {
+    return $this->condition->conditions();
+  }
+
+  /**
+   * Implements QueryConditionInterface::arguments().
+   */
+  public function arguments() {
+    return $this->condition->arguments();
+  }
+
+  /**
+   * Implements QueryConditionInterface::where().
+   */
+  public function where($snippet, $args = array()) {
+    $this->condition->where($snippet, $args);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::compile().
+   */
+  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) {
+    return $this->condition->compile($connection, $queryPlaceholder);
+  }
+
+  /**
+   * Implements QueryConditionInterface::compiled().
+   */
+  public function compiled() {
+    return $this->condition->compiled();
+  }
+
+  /**
+   * Executes the DELETE query.
+   *
+   * @return int
+   *   The number of rows affected by the delete query.
+   */
+  public function execute() {
+    $values = array();
+    if (count($this->condition)) {
+      $this->condition->compile($this->connection, $this);
+      $values = $this->condition->arguments();
+    }
+
+    return $this->connection->query((string) $this, $values, $this->queryOptions);
+  }
+
+  /**
+   * Implements PHP magic __toString method to convert the query to a string.
+   *
+   * @return string
+   *   The prepared statement.
+   */
+  public function __toString() {
+    // Create a sanitized comment string to prepend to the query.
+    $comments = $this->connection->makeComment($this->comments);
+
+    $query = $comments . 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '} ';
+
+    if (count($this->condition)) {
+
+      $this->condition->compile($this->connection, $this);
+      $query .= "\nWHERE " . $this->condition;
+    }
+
+    return $query;
+  }
+}
+
+
+/**
+ * General class for an abstracted TRUNCATE operation.
+ */
+class TruncateQuery extends Query {
+
+  /**
+   * The table to truncate.
+   *
+   * @var string
+   */
+  protected $table;
+
+  /**
+   * Constructs a TruncateQuery object.
+   *
+   * @param DatabaseConnection $connection
+   *   A DatabaseConnection object.
+   * @param string $table
+   *   Name of the table to associate with this query.
+   * @param array $options
+   *   Array of database options.
+   */
+  public function __construct(DatabaseConnection $connection, $table, array $options = array()) {
+    $options['return'] = Database::RETURN_AFFECTED;
+    parent::__construct($connection, $options);
+    $this->table = $table;
+  }
+
+  /**
+   * Implements QueryConditionInterface::compile().
+   */
+  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) {
+    return $this->condition->compile($connection, $queryPlaceholder);
+  }
+
+  /**
+   * Implements QueryConditionInterface::compiled().
+   */
+  public function compiled() {
+    return $this->condition->compiled();
+  }
+
+  /**
+   * Executes the TRUNCATE query.
+   *
+   * @return
+   *   Return value is dependent on the database type.
+   */
+  public function execute() {
+    return $this->connection->query((string) $this, array(), $this->queryOptions);
+  }
+
+  /**
+   * Implements PHP magic __toString method to convert the query to a string.
+   *
+   * @return string
+   *   The prepared statement.
+   */
+  public function __toString() {
+    // Create a sanitized comment string to prepend to the query.
+    $comments = $this->connection->makeComment($this->comments);
+
+    // In most cases, TRUNCATE is not a transaction safe statement as it is a
+    // DDL statement which results in an implicit COMMIT. When we are in a
+    // transaction, fallback to the slower, but transactional, DELETE.
+    // PostgreSQL also locks the entire table for a TRUNCATE strongly reducing
+    // the concurrency with other transactions.
+    if ($this->connection->inTransaction()) {
+      return $comments . 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '}';
+    }
+    else {
+      return $comments . 'TRUNCATE {' . $this->connection->escapeTable($this->table) . '} ';
+    }
+  }
+}
+
+/**
+ * General class for an abstracted UPDATE operation.
+ */
+class UpdateQuery extends Query implements QueryConditionInterface {
+
+  /**
+   * The table to update.
+   *
+   * @var string
+   */
+  protected $table;
+
+  /**
+   * An array of fields that will be updated.
+   *
+   * @var array
+   */
+  protected $fields = array();
+
+  /**
+   * An array of values to update to.
+   *
+   * @var array
+   */
+  protected $arguments = array();
+
+  /**
+   * The condition object for this query.
+   *
+   * Condition handling is handled via composition.
+   *
+   * @var DatabaseCondition
+   */
+  protected $condition;
+
+  /**
+   * Array of fields to update to an expression in case of a duplicate record.
+   *
+   * This variable is a nested array in the following format:
+   * @code
+   * <some field> => array(
+   *  'condition' => <condition to execute, as a string>,
+   *  'arguments' => <array of arguments for condition, or NULL for none>,
+   * );
+   * @endcode
+   *
+   * @var array
+   */
+  protected $expressionFields = array();
+
+  /**
+   * Constructs an UpdateQuery object.
+   *
+   * @param DatabaseConnection $connection
+   *   A DatabaseConnection object.
+   * @param string $table
+   *   Name of the table to associate with this query.
+   * @param array $options
+   *   Array of database options.
+   */
+  public function __construct(DatabaseConnection $connection, $table, array $options = array()) {
+    $options['return'] = Database::RETURN_AFFECTED;
+    parent::__construct($connection, $options);
+    $this->table = $table;
+
+    $this->condition = new DatabaseCondition('AND');
+  }
+
+  /**
+   * Implements QueryConditionInterface::condition().
+   */
+  public function condition($field, $value = NULL, $operator = NULL) {
+    $this->condition->condition($field, $value, $operator);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNull().
+   */
+  public function isNull($field) {
+    $this->condition->isNull($field);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNotNull().
+   */
+  public function isNotNull($field) {
+    $this->condition->isNotNull($field);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::exists().
+   */
+  public function exists(SelectQueryInterface $select) {
+    $this->condition->exists($select);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::notExists().
+   */
+  public function notExists(SelectQueryInterface $select) {
+    $this->condition->notExists($select);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::conditions().
+   */
+  public function &conditions() {
+    return $this->condition->conditions();
+  }
+
+  /**
+   * Implements QueryConditionInterface::arguments().
+   */
+  public function arguments() {
+    return $this->condition->arguments();
+  }
+
+  /**
+   * Implements QueryConditionInterface::where().
+   */
+  public function where($snippet, $args = array()) {
+    $this->condition->where($snippet, $args);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::compile().
+   */
+  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) {
+    return $this->condition->compile($connection, $queryPlaceholder);
+  }
+
+  /**
+   * Implements QueryConditionInterface::compiled().
+   */
+  public function compiled() {
+    return $this->condition->compiled();
+  }
+
+  /**
+   * Adds a set of field->value pairs to be updated.
+   *
+   * @param $fields
+   *   An associative array of fields to write into the database. The array keys
+   *   are the field names and the values are the values to which to set them.
+   *
+   * @return UpdateQuery
+   *   The called object.
+   */
+  public function fields(array $fields) {
+    $this->fields = $fields;
+    return $this;
+  }
+
+  /**
+   * Specifies fields to be updated as an expression.
+   *
+   * Expression fields are cases such as counter=counter+1. This method takes
+   * precedence over fields().
+   *
+   * @param $field
+   *   The field to set.
+   * @param $expression
+   *   The field will be set to the value of this expression. This parameter
+   *   may include named placeholders.
+   * @param $arguments
+   *   If specified, this is an array of key/value pairs for named placeholders
+   *   corresponding to the expression.
+   *
+   * @return UpdateQuery
+   *   The called object.
+   */
+  public function expression($field, $expression, array $arguments = NULL) {
+    $this->expressionFields[$field] = array(
+      'expression' => $expression,
+      'arguments' => $arguments,
+    );
+
+    return $this;
+  }
+
+  /**
+   * Executes the UPDATE query.
+   *
+   * @return
+   *   The number of rows affected by the update.
+   */
+  public function execute() {
+
+    // Expressions take priority over literal fields, so we process those first
+    // and remove any literal fields that conflict.
+    $fields = $this->fields;
+    $update_values = array();
+    foreach ($this->expressionFields as $field => $data) {
+      if (!empty($data['arguments'])) {
+        $update_values += $data['arguments'];
+      }
+      unset($fields[$field]);
+    }
+
+    // Because we filter $fields the same way here and in __toString(), the
+    // placeholders will all match up properly.
+    $max_placeholder = 0;
+    foreach ($fields as $field => $value) {
+      $update_values[':db_update_placeholder_' . ($max_placeholder++)] = $value;
+    }
+
+    if (count($this->condition)) {
+      $this->condition->compile($this->connection, $this);
+      $update_values = array_merge($update_values, $this->condition->arguments());
+    }
+
+    return $this->connection->query((string) $this, $update_values, $this->queryOptions);
+  }
+
+  /**
+   * Implements PHP magic __toString method to convert the query to a string.
+   *
+   * @return string
+   *   The prepared statement.
+   */
+  public function __toString() {
+    // Create a sanitized comment string to prepend to the query.
+    $comments = $this->connection->makeComment($this->comments);
+
+    // Expressions take priority over literal fields, so we process those first
+    // and remove any literal fields that conflict.
+    $fields = $this->fields;
+    $update_fields = array();
+    foreach ($this->expressionFields as $field => $data) {
+      $update_fields[] = $field . '=' . $data['expression'];
+      unset($fields[$field]);
+    }
+
+    $max_placeholder = 0;
+    foreach ($fields as $field => $value) {
+      $update_fields[] = $field . '=:db_update_placeholder_' . ($max_placeholder++);
+    }
+
+    $query = $comments . 'UPDATE {' . $this->connection->escapeTable($this->table) . '} SET ' . implode(', ', $update_fields);
+
+    if (count($this->condition)) {
+      $this->condition->compile($this->connection, $this);
+      // There is an implicit string cast on $this->condition.
+      $query .= "\nWHERE " . $this->condition;
+    }
+
+    return $query;
+  }
+
+}
+
+/**
+ * General class for an abstracted MERGE query operation.
+ *
+ * An ANSI SQL:2003 compatible database would run the following query:
+ *
+ * @code
+ * MERGE INTO table_name_1 USING table_name_2 ON (condition)
+ *   WHEN MATCHED THEN
+ *   UPDATE SET column1 = value1 [, column2 = value2 ...]
+ *   WHEN NOT MATCHED THEN
+ *   INSERT (column1 [, column2 ...]) VALUES (value1 [, value2 ...
+ * @endcode
+ *
+ * Other databases (most notably MySQL, PostgreSQL and SQLite) will emulate
+ * this statement by running a SELECT and then INSERT or UPDATE.
+ *
+ * By default, the two table names are identical and they are passed into the
+ * the constructor. table_name_2 can be specified by the
+ * MergeQuery::conditionTable() method. It can be either a string or a
+ * subquery.
+ *
+ * The condition is built exactly like SelectQuery or UpdateQuery conditions,
+ * the UPDATE query part is built similarly like an UpdateQuery and finally the
+ * INSERT query part is built similarly like an InsertQuery. However, both
+ * UpdateQuery and InsertQuery has a fields method so
+ * MergeQuery::updateFields() and MergeQuery::insertFields() needs to be called
+ * instead. MergeQuery::fields() can also be called which calls both of these
+ * methods as the common case is to use the same column-value pairs for both
+ * INSERT and UPDATE. However, this is not mandatory. Another convenient
+ * wrapper is MergeQuery::key() which adds the same column-value pairs to the
+ * condition and the INSERT query part.
+ *
+ * Several methods (key(), fields(), insertFields()) can be called to set a
+ * key-value pair for the INSERT query part. Subsequent calls for the same
+ * fields override the earlier ones. The same is true for UPDATE and key(),
+ * fields() and updateFields().
+ */
+class MergeQuery extends Query implements QueryConditionInterface {
+  /**
+   * Returned by execute() if an INSERT query has been executed.
+   */
+  const STATUS_INSERT = 1;
+
+  /**
+   * Returned by execute() if an UPDATE query has been executed.
+   */
+  const STATUS_UPDATE = 2;
+
+  /**
+   * The table to be used for INSERT and UPDATE.
+   *
+   * @var string
+   */
+  protected $table;
+
+  /**
+   * The table or subquery to be used for the condition.
+   */
+  protected $conditionTable;
+
+  /**
+   * An array of fields on which to insert.
+   *
+   * @var array
+   */
+  protected $insertFields = array();
+
+  /**
+   * An array of fields which should be set to their database-defined defaults.
+   *
+   * Used on INSERT.
+   *
+   * @var array
+   */
+  protected $defaultFields = array();
+
+  /**
+   * An array of values to be inserted.
+   *
+   * @var string
+   */
+  protected $insertValues = array();
+
+  /**
+   * An array of fields that will be updated.
+   *
+   * @var array
+   */
+  protected $updateFields = array();
+
+  /**
+   * Array of fields to update to an expression in case of a duplicate record.
+   *
+   * This variable is a nested array in the following format:
+   * @code
+   * <some field> => array(
+   *  'condition' => <condition to execute, as a string>,
+   *  'arguments' => <array of arguments for condition, or NULL for none>,
+   * );
+   * @endcode
+   *
+   * @var array
+   */
+  protected $expressionFields = array();
+
+  /**
+   * Flag indicating whether an UPDATE is necessary.
+   *
+   * @var boolean
+   */
+  protected $needsUpdate = FALSE;
+
+  /**
+  * Constructs a MergeQuery object.
+  *
+  * @param DatabaseConnection $connection
+  *   A DatabaseConnection object.
+  * @param string $table
+  *   Name of the table to associate with this query.
+  * @param array $options
+  *   Array of database options.
+  */
+  public function __construct(DatabaseConnection $connection, $table, array $options = array()) {
+    $options['return'] = Database::RETURN_AFFECTED;
+    parent::__construct($connection, $options);
+    $this->table = $table;
+    $this->conditionTable = $table;
+    $this->condition = new DatabaseCondition('AND');
+  }
+
+  /**
+   * Sets the table or subquery to be used for the condition.
+   *
+   * @param $table
+   *   The table name or the subquery to be used. Use a SelectQuery object to
+   *   pass in a subquery.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  protected function conditionTable($table) {
+    $this->conditionTable = $table;
+    return $this;
+  }
+
+  /**
+   * Adds a set of field->value pairs to be updated.
+   *
+   * @param $fields
+   *   An associative array of fields to write into the database. The array keys
+   *   are the field names and the values are the values to which to set them.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  public function updateFields(array $fields) {
+    $this->updateFields = $fields;
+    $this->needsUpdate = TRUE;
+    return $this;
+  }
+
+  /**
+   * Specifies fields to be updated as an expression.
+   *
+   * Expression fields are cases such as counter = counter + 1. This method
+   * takes precedence over MergeQuery::updateFields() and it's wrappers,
+   * MergeQuery::key() and MergeQuery::fields().
+   *
+   * @param $field
+   *   The field to set.
+   * @param $expression
+   *   The field will be set to the value of this expression. This parameter
+   *   may include named placeholders.
+   * @param $arguments
+   *   If specified, this is an array of key/value pairs for named placeholders
+   *   corresponding to the expression.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  public function expression($field, $expression, array $arguments = NULL) {
+    $this->expressionFields[$field] = array(
+      'expression' => $expression,
+      'arguments' => $arguments,
+    );
+    $this->needsUpdate = TRUE;
+    return $this;
+  }
+
+  /**
+   * Adds a set of field->value pairs to be inserted.
+   *
+   * @param $fields
+   *   An array of fields on which to insert. This array may be indexed or
+   *   associative. If indexed, the array is taken to be the list of fields.
+   *   If associative, the keys of the array are taken to be the fields and
+   *   the values are taken to be corresponding values to insert. If a
+   *   $values argument is provided, $fields must be indexed.
+   * @param $values
+   *   An array of fields to insert into the database. The values must be
+   *   specified in the same order as the $fields array.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  public function insertFields(array $fields, array $values = array()) {
+    if ($values) {
+      $fields = array_combine($fields, $values);
+    }
+    $this->insertFields = $fields;
+    return $this;
+  }
+
+  /**
+   * Specifies fields for which the database-defaults should be used.
+   *
+   * If you want to force a given field to use the database-defined default,
+   * not NULL or undefined, use this method to instruct the database to use
+   * default values explicitly. In most cases this will not be necessary
+   * unless you are inserting a row that is all default values, as you cannot
+   * specify no values in an INSERT query.
+   *
+   * Specifying a field both in fields() and in useDefaults() is an error
+   * and will not execute.
+   *
+   * @param $fields
+   *   An array of values for which to use the default values
+   *   specified in the table definition.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  public function useDefaults(array $fields) {
+    $this->defaultFields = $fields;
+    return $this;
+  }
+
+  /**
+   * Sets common field-value pairs in the INSERT and UPDATE query parts.
+   *
+   * This method should only be called once. It may be called either
+   * with a single associative array or two indexed arrays. If called
+   * with an associative array, the keys are taken to be the fields
+   * and the values are taken to be the corresponding values to set.
+   * If called with two arrays, the first array is taken as the fields
+   * and the second array is taken as the corresponding values.
+   *
+   * @param $fields
+   *   An array of fields to insert, or an associative array of fields and
+   *   values. The keys of the array are taken to be the fields and the values
+   *   are taken to be corresponding values to insert.
+   * @param $values
+   *   An array of values to set into the database. The values must be
+   *   specified in the same order as the $fields array.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  public function fields(array $fields, array $values = array()) {
+    if ($values) {
+      $fields = array_combine($fields, $values);
+    }
+    foreach ($fields as $key => $value) {
+      $this->insertFields[$key] = $value;
+      $this->updateFields[$key] = $value;
+    }
+    $this->needsUpdate = TRUE;
+    return $this;
+  }
+
+  /**
+   * Sets the key field(s) to be used as conditions for this query.
+   *
+   * This method should only be called once. It may be called either
+   * with a single associative array or two indexed arrays. If called
+   * with an associative array, the keys are taken to be the fields
+   * and the values are taken to be the corresponding values to set.
+   * If called with two arrays, the first array is taken as the fields
+   * and the second array is taken as the corresponding values.
+   *
+   * The fields are copied to the condition of the query and the INSERT part.
+   * If no other method is called, the UPDATE will become a no-op.
+   *
+   * @param $fields
+   *   An array of fields to set, or an associative array of fields and values.
+   * @param $values
+   *   An array of values to set into the database. The values must be
+   *   specified in the same order as the $fields array.
+   *
+   * @return MergeQuery
+   *   The called object.
+   */
+  public function key(array $fields, array $values = array()) {
+    if ($values) {
+      $fields = array_combine($fields, $values);
+    }
+    foreach ($fields as $key => $value) {
+      $this->insertFields[$key] = $value;
+      $this->condition($key, $value);
+    }
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::condition().
+   */
+  public function condition($field, $value = NULL, $operator = NULL) {
+    $this->condition->condition($field, $value, $operator);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNull().
+   */
+  public function isNull($field) {
+    $this->condition->isNull($field);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNotNull().
+   */
+  public function isNotNull($field) {
+    $this->condition->isNotNull($field);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::exists().
+   */
+  public function exists(SelectQueryInterface $select) {
+    $this->condition->exists($select);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::notExists().
+   */
+  public function notExists(SelectQueryInterface $select) {
+    $this->condition->notExists($select);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::conditions().
+   */
+  public function &conditions() {
+    return $this->condition->conditions();
+  }
+
+  /**
+   * Implements QueryConditionInterface::arguments().
+   */
+  public function arguments() {
+    return $this->condition->arguments();
+  }
+
+  /**
+   * Implements QueryConditionInterface::where().
+   */
+  public function where($snippet, $args = array()) {
+    $this->condition->where($snippet, $args);
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::compile().
+   */
+  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) {
+    return $this->condition->compile($connection, $queryPlaceholder);
+  }
+
+  /**
+   * Implements QueryConditionInterface::compiled().
+   */
+  public function compiled() {
+    return $this->condition->compiled();
+  }
+
+  /**
+   * Implements PHP magic __toString method to convert the query to a string.
+   *
+   * In the degenerate case, there is no string-able query as this operation
+   * is potentially two queries.
+   *
+   * @return string
+   *   The prepared query statement.
+   */
+  public function __toString() {
+  }
+
+  public function execute() {
+    if (!count($this->condition)) {
+      throw new InvalidMergeQueryException(t('Invalid merge query: no conditions'));
+    }
+    $select = $this->connection->select($this->conditionTable)
+      ->condition($this->condition);
+    $select->addExpression('1');
+    if (!$select->execute()->fetchField()) {
+      try {
+        $insert = $this->connection->insert($this->table)->fields($this->insertFields);
+        if ($this->defaultFields) {
+          $insert->useDefaults($this->defaultFields);
+        }
+        $insert->execute();
+        return self::STATUS_INSERT;
+      }
+      catch (Exception $e) {
+        // The insert query failed, maybe it's because a racing insert query
+        // beat us in inserting the same row. Retry the select query, if it
+        // returns a row, ignore the error and continue with the update
+        // query below.
+        if (!$select->execute()->fetchField()) {
+          throw $e;
+        }
+      }
+    }
+    if ($this->needsUpdate) {
+      $update = $this->connection->update($this->table)
+        ->fields($this->updateFields)
+        ->condition($this->condition);
+      if ($this->expressionFields) {
+        foreach ($this->expressionFields as $field => $data) {
+          $update->expression($field, $data['expression'], $data['arguments']);
+        }
+      }
+      $update->execute();
+      return self::STATUS_UPDATE;
+     }
+  }
+}
+
+/**
+ * Generic class for a series of conditions in a query.
+ */
+class DatabaseCondition implements QueryConditionInterface, Countable {
+
+  /**
+   * Array of conditions.
+   *
+   * @var array
+   */
+  protected $conditions = array();
+
+  /**
+   * Array of arguments.
+   *
+   * @var array
+   */
+  protected $arguments = array();
+
+  /**
+   * Whether the conditions have been changed.
+   *
+   * TRUE if the condition has been changed since the last compile.
+   * FALSE if the condition has been compiled and not changed.
+   *
+   * @var bool
+   */
+  protected $changed = TRUE;
+
+  /**
+   * The identifier of the query placeholder this condition has been compiled against.
+   */
+  protected $queryPlaceholderIdentifier;
+
+  /**
+   * Constructs a DataBaseCondition object.
+   *
+   * @param string $conjunction
+   *   The operator to use to combine conditions: 'AND' or 'OR'.
+   */
+  public function __construct($conjunction) {
+    $this->conditions['#conjunction'] = $conjunction;
+  }
+
+  /**
+   * Implements Countable::count().
+   *
+   * Returns the size of this conditional. The size of the conditional is the
+   * size of its conditional array minus one, because one element is the
+   * conjunction.
+   */
+  public function count() {
+    return count($this->conditions) - 1;
+  }
+
+  /**
+   * Implements QueryConditionInterface::condition().
+   */
+  public function condition($field, $value = NULL, $operator = NULL) {
+    if (!isset($operator)) {
+      if (is_array($value)) {
+        $operator = 'IN';
+      }
+      elseif (!isset($value)) {
+        $operator = 'IS NULL';
+      }
+      else {
+        $operator = '=';
+      }
+    }
+    $this->conditions[] = array(
+      'field' => $field,
+      'value' => $value,
+      'operator' => $operator,
+    );
+
+    $this->changed = TRUE;
+
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::where().
+   */
+  public function where($snippet, $args = array()) {
+    $this->conditions[] = array(
+      'field' => $snippet,
+      'value' => $args,
+      'operator' => NULL,
+    );
+    $this->changed = TRUE;
+
+    return $this;
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNull().
+   */
+  public function isNull($field) {
+    return $this->condition($field);
+  }
+
+  /**
+   * Implements QueryConditionInterface::isNotNull().
+   */
+  public function isNotNull($field) {
+    return $this->condition($field, NULL, 'IS NOT NULL');
+  }
+
+  /**
+   * Implements QueryConditionInterface::exists().
+   */
+  public function exists(SelectQueryInterface $select) {
+    return $this->condition('', $select, 'EXISTS');
+  }
+
+  /**
+   * Implements QueryConditionInterface::notExists().
+   */
+  public function notExists(SelectQueryInterface $select) {
+    return $this->condition('', $select, 'NOT EXISTS');
+  }
+
+  /**
+   * Implements QueryConditionInterface::conditions().
+   */
+  public function &conditions() {
+    return $this->conditions;
+  }
+
+  /**
+   * Implements QueryConditionInterface::arguments().
+   */
+  public function arguments() {
+    // If the caller forgot to call compile() first, refuse to run.
+    if ($this->changed) {
+      return NULL;
+    }
+    return $this->arguments;
+  }
+
+  /**
+   * Implements QueryConditionInterface::compile().
+   */
+  public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) {
+    // Re-compile if this condition changed or if we are compiled against a
+    // different query placeholder object.
+    if ($this->changed || isset($this->queryPlaceholderIdentifier) && ($this->queryPlaceholderIdentifier != $queryPlaceholder->uniqueIdentifier())) {
+      $this->queryPlaceholderIdentifier = $queryPlaceholder->uniqueIdentifier();
+
+      $condition_fragments = array();
+      $arguments = array();
+
+      $conditions = $this->conditions;
+      $conjunction = $conditions['#conjunction'];
+      unset($conditions['#conjunction']);
+      foreach ($conditions as $condition) {
+        if (empty($condition['operator'])) {
+          // This condition is a literal string, so let it through as is.
+          $condition_fragments[] = ' (' . $condition['field'] . ') ';
+          $arguments += $condition['value'];
+        }
+        else {
+          // It's a structured condition, so parse it out accordingly.
+          // Note that $condition['field'] will only be an object for a dependent
+          // DatabaseCondition object, not for a dependent subquery.
+          if ($condition['field'] instanceof QueryConditionInterface) {
+            // Compile the sub-condition recursively and add it to the list.
+            $condition['field']->compile($connection, $queryPlaceholder);
+            $condition_fragments[] = '(' . (string) $condition['field'] . ')';
+            $arguments += $condition['field']->arguments();
+          }
+          else {
+            // For simplicity, we treat all operators as the same data structure.
+            // In the typical degenerate case, this won't get changed.
+            $operator_defaults = array(
+              'prefix' => '',
+              'postfix' => '',
+              'delimiter' => '',
+              'operator' => $condition['operator'],
+              'use_value' => TRUE,
+            );
+            $operator = $connection->mapConditionOperator($condition['operator']);
+            if (!isset($operator)) {
+              $operator = $this->mapConditionOperator($condition['operator']);
+            }
+            $operator += $operator_defaults;
+
+            $placeholders = array();
+            if ($condition['value'] instanceof SelectQueryInterface) {
+              $condition['value']->compile($connection, $queryPlaceholder);
+              $placeholders[] = (string) $condition['value'];
+              $arguments += $condition['value']->arguments();
+              // Subqueries are the actual value of the operator, we don't
+              // need to add another below.
+              $operator['use_value'] = FALSE;
+            }
+            // We assume that if there is a delimiter, then the value is an
+            // array. If not, it is a scalar. For simplicity, we first convert
+            // up to an array so that we can build the placeholders in the same way.
+            elseif (!$operator['delimiter']) {
+              $condition['value'] = array($condition['value']);
+            }
+            if ($operator['use_value']) {
+              foreach ($condition['value'] as $value) {
+                $placeholder = ':db_condition_placeholder_' . $queryPlaceholder->nextPlaceholder();
+                $arguments[$placeholder] = $value;
+                $placeholders[] = $placeholder;
+              }
+            }
+            $condition_fragments[] = ' (' . $connection->escapeField($condition['field']) . ' ' . $operator['operator'] . ' ' . $operator['prefix'] . implode($operator['delimiter'], $placeholders) . $operator['postfix'] . ') ';
+          }
+        }
+      }
+
+      $this->changed = FALSE;
+      $this->stringVersion = implode($conjunction, $condition_fragments);
+      $this->arguments = $arguments;
+    }
+  }
+
+  /**
+   * Implements QueryConditionInterface::compiled().
+   */
+  public function compiled() {
+    return !$this->changed;
+  }
+
+  /**
+   * Implements PHP magic __toString method to convert the conditions to string.
+   *
+   * @return string
+   *   A string version of the conditions.
+   */
+  public function __toString() {
+    // If the caller forgot to call compile() first, refuse to run.
+    if ($this->changed) {
+      return NULL;
+    }
+    return $this->stringVersion;
+  }
+
+  /**
+   * PHP magic __clone() method.
+   *
+   * Only copies fields that implement QueryConditionInterface. Also sets
+   * $this->changed to TRUE.
+   */
+  function __clone() {
+    $this->changed = TRUE;
+    foreach ($this->conditions as $key => $condition) {
+      if ($key !== '#conjunction') {
+        if ($condition['field'] instanceOf QueryConditionInterface) {
+          $this->conditions[$key]['field'] = clone($condition['field']);
+        }
+        if ($condition['value'] instanceOf SelectQueryInterface) {
+          $this->conditions[$key]['value'] = clone($condition['value']);
+        }
+      }
+    }
+  }
+
+  /**
+   * Gets any special processing requirements for the condition operator.
+   *
+   * Some condition types require special processing, such as IN, because
+   * the value data they pass in is not a simple value. This is a simple
+   * overridable lookup function.
+   *
+   * @param $operator
+   *   The condition operator, such as "IN", "BETWEEN", etc. Case-sensitive.
+   *
+   * @return
+   *   The extra handling directives for the specified operator, or NULL.
+   */
+  protected function mapConditionOperator($operator) {
+    // $specials does not use drupal_static as its value never changes.
+    static $specials = array(
+      'BETWEEN' => array('delimiter' => ' AND '),
+      'IN' => array('delimiter' => ', ', 'prefix' => ' (', 'postfix' => ')'),
+      'NOT IN' => array('delimiter' => ', ', 'prefix' => ' (', 'postfix' => ')'),
+      'EXISTS' => array('prefix' => ' (', 'postfix' => ')'),
+      'NOT EXISTS' => array('prefix' => ' (', 'postfix' => ')'),
+      'IS NULL' => array('use_value' => FALSE),
+      'IS NOT NULL' => array('use_value' => FALSE),
+      // Use backslash for escaping wildcard characters.
+      'LIKE' => array('postfix' => " ESCAPE '\\\\'"),
+      'NOT LIKE' => array('postfix' => " ESCAPE '\\\\'"),
+      // These ones are here for performance reasons.
+      '=' => array(),
+      '<' => array(),
+      '>' => array(),
+      '>=' => array(),
+      '<=' => array(),
+    );
+    if (isset($specials[$operator])) {
+      $return = $specials[$operator];
+    }
+    else {
+      // We need to upper case because PHP index matches are case sensitive but
+      // do not need the more expensive drupal_strtoupper because SQL statements are ASCII.
+      $operator = strtoupper($operator);
+      $return = isset($specials[$operator]) ? $specials[$operator] : array();
+    }
+
+    $return += array('operator' => $operator);
+
+    return $return;
+  }
+
+}
+
+/**
+ * @} End of "addtogroup database".
+ */