<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
/**
* CodeIgniter
*
* An open source application development framework for PHP 5.1.6 or newer
*
* @package CodeIgniter
* @author ExpressionEngine Dev Team
* @copyright Copyright (c) 2008 - 2011, EllisLab, Inc.
* @license http://codeigniter.com/user_guide/license.html
* @link http://codeigniter.com
* @since Version 1.0
* @filesource
*/
// ------------------------------------------------------------------------
/**
* MySQL Database Adapter Class
*
* mysql 数据库的适配器类
*
* Note: _DB is an extender class that the app controller
* creates dynamically based on whether the active record
* class is being used or not.
*
* 注：_DB是一个扩展类应用控制器
* 创建动态的基础上是否活动记录类正在使用与否。
* @package CodeIgniter
* @subpackage Drivers
* @category Database
* @author ExpressionEngine Dev Team
* @link http://codeigniter.com/user_guide/database/
*/
class CI_DB_mysql_driver extends CI_DB {
var $dbdriver = 'mysql'; //数据库类型
// The character used for escaping 用于转义字符
var $_escape_char = '`';
// clause and character used for LIKE escape sequences - not used in MySQL
// 在MySQL中使用条款和字符用于LIKE转义序列 -
var $_like_escape_str = '';
var $_like_escape_chr = '';
/**
* Whether to use the MySQL "delete hack" which allows the number
* of affected rows to be shown. Uses a preg_replace when enabled,
* adding a bit more processing to all queries.
* *是否使用MySQL的“删除”，它允许黑客的数量
* 受影响的行显示。 preg_replace函数使用一个启用时，
* 添加更多一点的处理所有的查询。
*/
var $delete_hack = TRUE;
/**
* The syntax to count rows is slightly different across different
* database engines, so this string appears in each driver and is
* used for the count_all() and count_all_results() functions.
* 在不同的数行的语法略有不同
* 数据库引擎，所以这个字符串出现在每个驱动器和
* 用于count_all（）和count_all_results（）函数。
*
*/
var $_count_string = 'SELECT COUNT(*) AS ';
var $_random_keyword = ' RAND()'; // database specific random keyword 数据库特定的随机关键字
// whether SET NAMES must be used to set the character set
// 是否SET名称必须使用设置字符集
var $use_set_names;
/**
* Non-persistent database connection
* 非持久性数据库连接
* @access private called by the base class 私人称为基类
* @return resource 返回资源
*/
function db_connect()
{
//发果接口不为空
if ($this->port != '')
{
//拼接到hostname后面
$this->hostname .= ':'.$this->port;
}
//返回一个数据库链接资源
return @mysql_connect($this->hostname, $this->username, $this->password, TRUE);
}
// --------------------------------------------------------------------
/**
* Persistent database connection
* 持久数据库连接
* @access private called by the base class
* @return resource
*/
function db_pconnect()
{
if ($this->port != '')
{
$this->hostname .= ':'.$this->port;
}
return @mysql_pconnect($this->hostname, $this->username, $this->password);
}
// --------------------------------------------------------------------
/**
* Reconnect
* 重新连接
*
* Keep / reestablish the db connection if no queries have been
* sent for a length of time exceeding the server's idle timeout
* 保持/重新建立数据库连接，如果没有查询
* 发送的时间长度超过服务器的空闲超时
* @access public
* @return void
*/
function reconnect()
{
//mysql_ping($this->conn_id) === false
//mysql_ping 检查与服务端的连接是否正常检查与服务端的连接是否正常。连接断开时，如果自动重新连接功能未被禁用，则尝试重新连接服务器。该函数可被客户端用来检测闲置许久以后，与服务端的连接是否关闭，如有需要，则重新连接。
if (mysql_ping($this->conn_id) === FALSE) //如果链接已经也断开
{
$this->conn_id = FALSE; //将链接资源设置为false
}
}
// --------------------------------------------------------------------
/**
* Select the database
* 选择数据库
*
* @access private called by the base class
* @return resource
*/
function db_select()
{
return @mysql_select_db($this->database, $this->conn_id);
}
// --------------------------------------------------------------------
/**
* Set client character set
* 设置客户端的字符编码
*
* @access public
* @param string
* @param string
* @return resource
*/
function db_set_charset($charset, $collation)
{
//如果没有设置字符
if ( ! isset($this->use_set_names))
{
// mysql_set_charset() requires PHP >= 5.2.3 and MySQL >= 5.0.7, use SET NAMES as fallback
// 在指定的php版本和mysql版本才能设置mysql_set_charset()函数
$this->use_set_names = (version_compare(PHP_VERSION, '5.2.3', '>=') && version_compare(mysql_get_server_info(), '5.0.7', '>=')) ? FALSE : TRUE;
}
if ($this->use_set_names === TRUE)
{
//合适的版本，设置 set names
return @mysql_query("SET NAMES '".$this->escape_str($charset)."' COLLATE '".$this->escape_str($collation)."'", $this->conn_id);
}
else
{
return @mysql_set_charset($charset, $this->conn_id);
}
}
// --------------------------------------------------------------------
/**
* Version number query string
* 取得版本信息
* @access public
* @return string
*/
function _version()
{
return "SELECT version() AS ver";
}
// --------------------------------------------------------------------
/**
* Execute the query
* 执行查询
*
* @access private called by the base class
* @param string an SQL query
* @return resource
*/
function _execute($sql)
{
$sql = $this->_prep_query($sql);
return @mysql_query($sql, $this->conn_id);
}
// --------------------------------------------------------------------
/**
* Prep the query
* 准备查询
*
* If needed, each database adapter can prep the query string
* 如果需要，每个数据库适配器可以预先准备的查询字符串
*
* @access private called by execute()
* @param string an SQL query
* @return string
*/
function _prep_query($sql)
{
// "DELETE FROM TABLE" returns 0 affected rows This hack modifies
// the query so that it returns the number of affected rows
// “DELETE FROM表”，返回受影响的行黑客修改
// 查询，以便它返回受影响的行数
// delete hack=破解
if ($this->delete_hack === TRUE)
{
//如果字符串是为什 delete + FROM 一些字符串
if (preg_match('/^\s*DELETE\s+FROM\s+(\S+)\s*$/i', $sql))
{
//替换为delete from 1 where 1=1
$sql = preg_replace("/^\s*DELETE\s+FROM\s+(\S+)\s*$/", "DELETE FROM \\1 WHERE 1=1", $sql);
}
}
return $sql;
}
// --------------------------------------------------------------------
/**
* Begin Transaction
* 开始交易
*
* @access public
* @return bool
*/
function trans_begin($test_mode = FALSE)
{
if ( ! $this->trans_enabled)
{
return TRUE;
}
// When transactions are nested we only begin/commit/rollback the outermost ones
// 当事务被嵌套，我们才开始/提交/回滚最外层的
if ($this->_trans_depth > 0)
{
return TRUE;
}
// Reset the transaction failure flag.
// If the $test_mode flag is set to TRUE transactions will be rolled back
// even if the queries produce a successful result.
// 复位的交易失败标志。
// 如果$ TEST_MODE标志设置为TRUE交易将回滚
// 即使查询产生一个成功的结果。
$this->_trans_failure = ($test_mode === TRUE) ? TRUE : FALSE;
//开始事务处理
//set AUTOCOMMIT=0 禁止自动提交
$this->simple_query('SET AUTOCOMMIT=0');
$this->simple_query('START TRANSACTION'); // can also be BEGIN or BEGIN WORK 也可以开始或开始工作
return TRUE;
}
// --------------------------------------------------------------------
/**
* Commit Transaction
* commit 事务
*
* @access public
* @return bool
*/
function trans_commit()
{
if ( ! $this->trans_enabled)
{
return TRUE;
}
// When transactions are nested we only begin/commit/rollback the outermost ones
// 当事务被嵌套，我们才开始/提交/回滚最外层的
if ($this->_trans_depth > 0)
{
return TRUE;
}
//COMMIT 确定一个事务
$this->simple_query('COMMIT');
//SET AUTOCOMMIT=1 开启自动提交
$this->simple_query('SET AUTOCOMMIT=1');
return TRUE;
}
// --------------------------------------------------------------------
/**
* Rollback Transaction
* 回滚事务
*
* @access public
* @return bool
*/
function trans_rollback()
{
if ( ! $this->trans_enabled)
{
return TRUE;
}
// When transactions are nested we only begin/commit/rollback the outermost ones
if ($this->_trans_depth > 0)
{
return TRUE;
}
//判断当前操作失败时回滚
//ROLLBACK 判断当前操作失败时回滚
$this->simple_query('ROLLBACK');
$this->simple_query('SET AUTOCOMMIT=1');
//set AUTOCOMMIT =1; 开启自动提交
return TRUE;
}
// --------------------------------------------------------------------
/**
* Escape String
* 转义字符串
* @access public
* @param string
* @param bool whether or not the string will be used in a LIKE condition
* @return string 是否该字符串将被用于在LIKE条件
*/
function escape_str($str, $like = FALSE)
{
//如果是数组 循环进行递归操作
if (is_array($str))
{
foreach ($str as $key => $val)
{
$str[$key] = $this->escape_str($val, $like);
}
return $str;
}
//判断是存存在mysql_real_escape_string函数
//mysql_real_escape_string() 函数转义sql语句中使用的字符串的特殊字符
/*
下列字符受影响：
\x00
\n
\r
\
'
"
\x1a
如果成功，则该函数返回被转义的字符串。如果失败，则返回 false。
* */
if (function_exists('mysql_real_escape_string') AND is_resource($this->conn_id))
{
$str = mysql_real_escape_string($str, $this->conn_id);
}
//mysql_escape_string() PHP 4 >= 4.0.3, PHP 5, 注意：在PHP5.3中已经弃用这种方法，不推荐使用
elseif (function_exists('mysql_escape_string'))
{
$str = mysql_escape_string($str);
}
else
{
$str = addslashes($str); //直接用addslashes操作
}
// escape LIKE condition wildcards
// 逃离LIKE条件通配符
if ($like === TRUE)
{
$str = str_replace(array('%', '_'), array('\\%', '\\_'), $str);
}
return $str;
}
// --------------------------------------------------------------------
/**
* Affected Rows
* 受影响的列 mysql_sffected_rows($this->conn_id)
* @access public
* @return integer
*/
function affected_rows()
{
return @mysql_affected_rows($this->conn_id);
}
// --------------------------------------------------------------------
/**
* Insert ID
* 最提插入的列id, 也就是取得最近一次插入数据的id号 mysql_insert_id($this->conn_id)
* @access public
* @return integer
*/
function insert_id()
{
return @mysql_insert_id($this->conn_id);
}
// --------------------------------------------------------------------
/**
* "Count All" query
* 获取所有查询
*
* Generates a platform-specific query string that counts all records in
* the specified database
* 生成一个平台特定的查询字符串中的所有记录计数指定的数据库
* @access public
* @param string
* @return string
*/
function count_all($table = '')
{
if ($table == '')
{
return 0;
}
// SELECT COUNT(*) AS numrows from tableName;
$query = $this->query($this->_count_string . $this->_protect_identifiers('numrows') . " FROM " . $this->_protect_identifiers($table, TRUE, NULL, FALSE));
//如果记录数为0
if ($query->num_rows() == 0)
{
return 0;
}
$row = $query->row(); //取得一行数据
$this->_reset_select(); //重置查询条件
return (int) $row->numrows; //返回记录总数
}
// --------------------------------------------------------------------
/**
* List table query
* 清单表查询
*
* Generates a platform-specific query string so that the table names can be fetched
* 生成一个特定于平台的查询字符串，以便可以获取表名
*
* @access private
* @param boolean
* @return string
*/
function _list_tables($prefix_limit = FALSE)
{
//取得数据库的所有表信息
$sql = "SHOW TABLES FROM ".$this->_escape_char.$this->database.$this->_escape_char;
//like 指定表名的数据
//SHOW tables FROM databasename like '%TB%'
if ($prefix_limit !== FALSE AND $this->dbprefix != '')
{
$sql .= " LIKE '".$this->escape_like_str($this->dbprefix)."%'";
}
return $sql;
}
// --------------------------------------------------------------------
/**
* Show column query
* 显示查询列信息
*
* Generates a platform-specific query string so that the column names can be fetched
* 生成一个特定于平台的查询字符串，所以也可以获取列名
*
* @access public
* @param string the table name
* @return string
*/
function _list_columns($table = '')
{
//show COLUMNS FROM tablename
return "SHOW COLUMNS FROM ".$this->_protect_identifiers($table, TRUE, NULL, FALSE);
}
// --------------------------------------------------------------------
/**
* Field data query
* 现场数据查询
* Generates a platform-specific query so that the column data can be retrieved
* 所以也可以检索列数据，生成特定平台查询
* @access public
* @param string the table name
* @return object
*/
function _field_data($table)
{
return "DESCRIBE ".$table;
}
// --------------------------------------------------------------------
/**
* The error message string
* 该错误消息字符串
* @access private
* @return string
*/
function _error_message()
{
return mysql_error($this->conn_id);
}
// --------------------------------------------------------------------
/**
* The error message number
* 该错误消息的数值
*
* @access private
* @return integer
*/
function _error_number()
{
return mysql_errno($this->conn_id);
}
// --------------------------------------------------------------------
/**
* Escape the SQL Identifiers
* 逃离SQL标识符
* This function escapes column and table names
* 此功能逃脱列和表名
* @access private
* @param string
* @return string
*/
function _escape_identifiers($item)
{
//如果为空，直接返回
if ($this->_escape_char == '')
{
return $item;
}
//
foreach ($this->_reserved_identifiers as $id)
{
//在teim中存在.加上$id的话，
if (strpos($item, '.'.$id) !== FALSE)
{
// ` + `.
// a.name;
//`a`.name
$str = $this->_escape_char. str_replace('.', $this->_escape_char.'.', $item);
// remove duplicates if the user already included the escape
// 删除重复，如果用户已经逃逸
// [`]+ 如果出现多次，那么`进行替换
return preg_replace('/['.$this->_escape_char.']+/', $this->_escape_char, $str);
}
}
//如果item中没有.
if (strpos($item, '.') !== FALSE)
{
// a.name
//`a`.`name`
$str = $this->_escape_char.str_replace('.', $this->_escape_char.'.'.$this->_escape_char, $item).$this->_escape_char;
}
else
{
$str = $this->_escape_char.$item.$this->_escape_char;
}
// remove duplicates if the user already included the escape
// 删除重复，如果用户已经逃逸
return preg_replace('/['.$this->_escape_char.']+/', $this->_escape_char, $str);
}
// --------------------------------------------------------------------
/**
* From Tables
*
* This function implicitly groups FROM tables so there is no confusion
* about operator precedence in harmony with SQL standards
* 此功能隐含团队从表所以没有混乱
* 运算符优先级在和谐与SQL标准
*
* @access public
* @param type
* @return type
*/
function _from_tables($tables)
{
if ( ! is_array($tables))
{
$tables = array($tables);
}
return '('.implode(', ', $tables).')';
}
// --------------------------------------------------------------------
/**
* Insert statement
* insert 语句
*
* Generates a platform-specific insert string from the supplied data
* 从所提供的数据，生成特定平台插入字符串
*
* @access public
* @param string the table name
* @param array the insert keys
* @param array the insert values
* @return string
*/
function _insert($table, $keys, $values)
{
return "INSERT INTO ".$table." (".implode(', ', $keys).") VALUES (".implode(', ', $values).")";
}
// --------------------------------------------------------------------
/**
* Replace statement
* 替换语句
*
* Generates a platform-specific replace string from the supplied data
* 从所提供的数据，生成一个特定于平台的替换字符串
*
* @access public
* @param string the table name
* @param array the insert keys
* @param array the insert values
* @return string
*/
function _replace($table, $keys, $values)
{
return "REPLACE INTO ".$table." (".implode(', ', $keys).") VALUES (".implode(', ', $values).")";
}
// --------------------------------------------------------------------
/**
* Insert_batch statement
* 插入批量语句
*
* Generates a platform-specific insert string from the supplied data
* 从所提供的数据，生成特定平台插入字符串
*
* @access public
* @param string the table name
* @param array the insert keys
* @param array the insert values
* @return string
*/
function _insert_batch($table, $keys, $values)
{
return "INSERT INTO ".$table." (".implode(', ', $keys).") VALUES ".implode(', ', $values);
}
// --------------------------------------------------------------------
/**
* Update statement
* 更新语句
*
* Generates a platform-specific update string from the supplied data
* 从所提供的数据，生成特定平台的更新字符串
*
* @access public
* @param string the table name
* @param array the update data
* @param array the where clause
* @param array the orderby clause
* @param array the limit clause
* @return string
*/
function _update($table, $values, $where, $orderby = array(), $limit = FALSE)
{
//对$values的值进行拼接
foreach ($values as $key => $val)
{
$valstr[] = $key . ' = ' . $val;
}
//如果有 limit
$limit = ( ! $limit) ? '' : ' LIMIT '.$limit;
//如明 order by
$orderby = (count($orderby) >= 1)?' ORDER BY '.implode(", ", $orderby):'';
//开始拼接update 语句
$sql = "UPDATE ".$table." SET ".implode(', ', $valstr);
//如果有条件，where
$sql .= ($where != '' AND count($where) >=1) ? " WHERE ".implode(" ", $where) : '';
$sql .= $orderby.$limit;
return $sql;
}
// --------------------------------------------------------------------
/**
* Update_Batch statement
* 批量更新语句
*
* Generates a platform-specific batch update string from the supplied data
* 从所提供的数据，生成一个特定于平台的批量更新字串
*
* @access public
* @param string the table name
* @param array the update data
* @param array the where clause
* @return string
*/
function _update_batch($table, $values, $index, $where = NULL)
{
$ids = array();
//如果$where条件不为空，那么用空格拼接成字符串 后面加上AND
$where = ($where != '' AND count($where) >=1) ? implode(" ", $where).' AND ' : '';
//开始循环需要更新的值
foreach ($values as $key => $val)
{
$ids[] = $val[$index]; //取得$val中指定的索引值
//取得$val数组中的所有key值数组，并循环
foreach (array_keys($val) as $field)
{
//拼接成 WHEN......THEN......
//总算弄明白case when then 什么意思了，跟php 中的switch case差不多
if ($field != $index)
{
$final[$field][] = 'WHEN '.$index.' = '.$val[$index].' THEN '.$val[$field];
}
}
}
$sql = "UPDATE ".$table." SET ";
$cases = '';
//整个这个循环有点没弄清楚什么情
foreach ($final as $k => $v)
{
$cases .= $k.' = CASE '."\n";
foreach ($v as $row)
{
$cases .= $row."\n";
}
$cases .= 'ELSE '.$k.' END, ';
}
$sql .= substr($cases, 0, -2);
$sql .= ' WHERE '.$where.$index.' IN ('.implode(',', $ids).')';
return $sql;
}
// --------------------------------------------------------------------
/**
* Truncate statement
* 截断语句
*
* Generates a platform-specific truncate string from the supplied data
* If the database does not support the truncate() command
* This function maps to "DELETE FROM table"
* 从所提供的数据，生成一个特定于平台的截断字符串
* 如果数据库不支持的截断（）命令。
* 此功能映射到“DELETE FROM表”
* @access public
* @param string the table name
* @return string
*/
function _truncate($table)
{
return "TRUNCATE ".$table;
//TRUNCATE talbename 是sql中的一个删除数据表内容的语句
}
// --------------------------------------------------------------------
/**
* Delete statement
*
* Generates a platform-specific delete string from the supplied data
* 从所提供的数据，生成一个特定于平台的删除字符串
*
* @access public
* @param string the table name
* @param array the where clause
* @param string the limit clause
* @return string
*/
function _delete($table, $where = array(), $like = array(), $limit = FALSE)
{
$conditions = '';
if (count($where) > 0 OR count($like) > 0)
{
$conditions = "\nWHERE ";
$conditions .= implode("\n", $this->ar_where);
if (count($where) > 0 && count($like) > 0)
{
$conditions .= " AND ";
}
$conditions .= implode("\n", $like);
}
$limit = ( ! $limit) ? '' : ' LIMIT '.$limit;
return "DELETE FROM ".$table.$conditions.$limit;
}
// --------------------------------------------------------------------
/**
* Limit string
*
* Generates a platform-specific LIMIT clause
* 生成特定平台的限制条款
* @access public
* @param string the sql query string
* @param integer the number of rows to limit the query to
* @param integer the offset value
* @return string
*/
function _limit($sql, $limit, $offset)
{
if ($offset == 0)
{
$offset = '';
}
else
{
$offset .= ", ";
}
return $sql."LIMIT ".$offset.$limit;
}
// --------------------------------------------------------------------
/**
* Close DB Connection
* 关闭数据库链接
* @access public
* @param resource
* @return void
*/
function _close($conn_id)
{
@mysql_close($conn_id);
}
}
/* End of file mysql_driver.php */
/* Location: ./system/database/drivers/mysql/mysql_driver.php */
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