diff --git a/core/lib/Drupal/Core/Database/StatementPrefetch.php b/core/lib/Drupal/Core/Database/StatementPrefetch.php
index af87d0d..92eab43 100644
--- a/core/lib/Drupal/Core/Database/StatementPrefetch.php
+++ b/core/lib/Drupal/Core/Database/StatementPrefetch.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Definition of Drupal\Core\Database\StatementPrefetch
+ * Definition of Drupal\Core\Database\StatementPrefetch.
  */
 
 namespace Drupal\Core\Database;
@@ -87,6 +87,7 @@ class StatementPrefetch implements \Iterator, StatementInterface {
 
   /**
    * Holds the current fetch style (which will be used by the next fetch).
+   *
    * @see \PDOStatement::fetch()
    *
    * @var int
@@ -131,6 +132,18 @@ class StatementPrefetch implements \Iterator, StatementInterface {
    */
   public $allowRowCount = FALSE;
 
+  /**
+   * Constructor for StatementPrefetch object.
+   *
+   * @param \PDO $pdo_connection
+   *   PDO database handler.
+   * @param \Drupal\Core\Database\Connection $connection
+   *   Drupal database connection object.
+   * @param string $query
+   *   Database query string.
+   * @param array $driver_options
+   *   Database driver options (optional).
+   */
   public function __construct(\PDO $pdo_connection, Connection $connection, $query, array $driver_options = array()) {
     $this->pdoConnection = $pdo_connection;
     $this->dbh = $connection;
@@ -141,11 +154,12 @@ public function __construct(\PDO $pdo_connection, Connection $connection, $query
   /**
    * Executes a prepared statement.
    *
-   * @param $args
-   *   An array of values with as many elements as there are bound parameters in the SQL statement being executed.
-   * @param $options
+   * @param array $args
+   *   An array of values with as many elements as there are bound parameters
+   *   in the SQL statement being executed.
+   * @param array $options
    *   An array of options for this query.
-   * @return
+   * @return bool
    *   TRUE on success, or FALSE on failure.
    */
   public function execute($args = array(), $options = array()) {
@@ -224,7 +238,7 @@ protected function throwPDOException() {
    * Some drivers (including SQLite) will need to perform some preparation
    * themselves to get the statement right.
    *
-   * @param $query
+   * @param string $query
    *   The query.
    * @param array $args
    *   An array of arguments.
@@ -243,6 +257,8 @@ public function getQueryString() {
   }
 
   /**
+   * Sets the fetch mode of the prefetch statement.
+   *
    * @see \PDOStatement::setFetchMode()
    */
   public function setFetchMode($fetchStyle, $a2 = NULL, $a3 = NULL) {
@@ -274,7 +290,7 @@ public function setFetchMode($fetchStyle, $a2 = NULL, $a3 = NULL) {
    * array position in $this->data and format it according to $this->fetchStyle
    * and $this->fetchMode.
    *
-   * @return
+   * @return mixed
    *  The current row formatted as requested.
    */
   public function current() {
@@ -327,16 +343,23 @@ public function current() {
     }
   }
 
-  /* Implementations of Iterator. */
-
+  /**
+   * {@inheritdoc}
+   */
   public function key() {
     return $this->currentKey;
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function rewind() {
     // Nothing to do: our DatabaseStatement can't be rewound.
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function next() {
     if (!empty($this->data)) {
       $this->currentRow = reset($this->data);
@@ -347,7 +370,9 @@ public function next() {
       $this->currentRow = NULL;
     }
   }
-
+  /**
+   * {@inheritdoc}
+   */
   public function valid() {
     return isset($this->currentRow);
   }
@@ -365,7 +390,19 @@ public function rowCount() {
     }
   }
 
-  public function fetch($fetch_style = NULL, $cursor_orientation = \PDO::FETCH_ORI_NEXT, $cursor_offset = NULL) {
+  /**
+   * Sets the default fetch mode for this statement.
+   *
+   * See http://php.net/manual/pdo.constants.php for the definition of the
+   * constants used.
+   *
+   * @param  $fetch_style (optional)
+   *   One of the \PDO::FETCH_* constants.
+   * @return mixed
+   *   Returns current row and sets record pointer to next record
+   *   or FALSE if there is no result set.
+   */
+  public function fetch($fetch_style = NULL) {
     if (isset($this->currentRow)) {
       // Set the fetch parameter.
       $this->fetchStyle = isset($fetch_style) ? $fetch_style : $this->defaultFetchStyle;
@@ -386,6 +423,14 @@ public function fetch($fetch_style = NULL, $cursor_orientation = \PDO::FETCH_ORI
     }
   }
 
+  /**
+   * Returns an entire single column of a result set as an indexed array.
+   *
+   * @param  int $index
+   *    The index of the column number to fetch.
+   * @return mixed
+   *    An indexed array, or FALSE if there is no result set.
+   */
   public function fetchColumn($index = 0) {
     if (isset($this->currentRow) && isset($this->columnNames[$index])) {
       // We grab the value directly from $this->data, and format it.
@@ -398,10 +443,27 @@ public function fetchColumn($index = 0) {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function fetchField($index = 0) {
     return $this->fetchColumn($index);
   }
 
+  /**
+   * Fetches the next row and returns it as an object.
+   *
+   * The object will be of the class specified by
+   * StatementInterface::setFetchMode() or stdClass if not specified.
+   *
+   * @param string $class_name
+   *    Name of class (optional).
+   * @param array $constructor_args
+   *    Constructor arguments (optional).
+   *
+   * @return mixed
+   *    result as an object or FALSE.
+   */
   public function fetchObject($class_name = NULL, $constructor_args = array()) {
     if (isset($this->currentRow)) {
       if (!isset($class_name)) {
@@ -427,6 +489,9 @@ public function fetchObject($class_name = NULL, $constructor_args = array()) {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function fetchAssoc() {
     if (isset($this->currentRow)) {
       $result = $this->currentRow;
@@ -438,6 +503,21 @@ public function fetchAssoc() {
     }
   }
 
+  /**
+   * Returns an array containing all of the result set rows.
+   *
+   * @param  mixed $fetch_style
+   *    One of the PDO::FETCH_* constants (optional).
+   * @param  int $fetch_column
+   *    If $mode is PDO::FETCH_COLUMN, the index of the column to
+   *    fetch (optional).
+   * @param  mixed $constructor_args
+   *    If $mode is PDO::FETCH_CLASS, the arguments to pass
+   *    to the constructor (optional).
+   *
+   * @return array
+   *   An array of result set.
+   */
   public function fetchAll($fetch_style = NULL, $fetch_column = NULL, $constructor_args = NULL) {
     $this->fetchStyle = isset($fetch_style) ? $fetch_style : $this->defaultFetchStyle;
     $this->fetchOptions = $this->defaultFetchOptions;
@@ -462,6 +542,9 @@ public function fetchAll($fetch_style = NULL, $fetch_column = NULL, $constructor
     return $result;
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function fetchCol($index = 0) {
     if (isset($this->columnNames[$index])) {
       $result = array();
@@ -477,6 +560,9 @@ public function fetchCol($index = 0) {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function fetchAllKeyed($key_index = 0, $value_index = 1) {
     if (!isset($this->columnNames[$key_index]) || !isset($this->columnNames[$value_index]))
       return array();
@@ -493,6 +579,9 @@ public function fetchAllKeyed($key_index = 0, $value_index = 1) {
     return $result;
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function fetchAllAssoc($key, $fetch_style = NULL) {
     $this->fetchStyle = isset($fetch_style) ? $fetch_style : $this->defaultFetchStyle;
     $this->fetchOptions = $this->defaultFetchOptions;