我正在尝试基于codeigniter中的会话变量加载其他数据库，但出现错误遇到错误您尚未选择要连接的数据库类型。下面有我的admin_init_elements库文件
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
/*
| -------------------------------------------------------------------
| DATABASE CONNECTIVITY SETTINGS
| -------------------------------------------------------------------
| This file will contain the settings needed to access your database.
|
| For complete instructions please consult the 'Database Connection'
| page of the User Guide.
|
| -------------------------------------------------------------------
| EXPLANATION OF VARIABLES
| -------------------------------------------------------------------
|
| ['hostname'] The hostname of your database server.
| ['username'] The username used to connect to the database
| ['password'] The password used to connect to the database
| ['database'] The name of the database you want to connect to
| ['dbdriver'] The database type. ie: mysql. Currently supported:
mysql, mysqli, postgre, odbc, mssql, sqlite, oci8
| ['dbprefix'] You can add an optional prefix, which will be added
| to the table name when using the Active Record class
| ['pconnect'] TRUE/FALSE - Whether to use a persistent connection
| ['db_debug'] TRUE/FALSE - Whether database errors should be displayed.
| ['cache_on'] TRUE/FALSE - Enables/disables query caching
| ['cachedir'] The path to the folder where cache files should be stored
| ['char_set'] The character set used in communicating with the database
| ['dbcollat'] The character collation used in communicating with the database
| NOTE: For MySQL and MySQLi databases, this setting is only used
| as a backup if your server is running PHP < 5.2.3 or MySQL < 5.0.7
| (and in table creation queries made with DB Forge).
| There is an incompatibility in PHP with mysql_real_escape_string() which
| can make your site vulnerable to SQL injection if you are using a
| multi-byte character set and are running versions lower than these.
| Sites using Latin-1 or UTF-8 database character set and collation are unaffected.
| ['swap_pre'] A default table prefix that should be swapped with the dbprefix
| ['autoinit'] Whether or not to automatically initialize the database.
| ['stricton'] TRUE/FALSE - forces 'Strict Mode' connections
| - good for ensuring strict SQL while developing
|
| The $active_group variable lets you choose which connection group to
| make active. By default there is only one group (the 'default' group).
|
| The $active_record variables lets you determine whether or not to load
| the active record class
*/
$active_group = 'default';
$active_record = TRUE;
$db['default']['hostname'] = 'localhost';
$db['default']['username'] = 'root';
$db['default']['password'] = 'pass';
$db['default']['database'] = 'latestdb';
$db['default']['dbdriver'] = 'mysql';
$db['default']['dbprefix'] = '';
$db['default']['pconnect'] = TRUE;
$db['default']['db_debug'] = TRUE;
$db['default']['cache_on'] = FALSE;
$db['default']['cachedir'] = '';
$db['default']['char_set'] = 'utf8';
$db['default']['dbcollat'] = 'utf8_general_ci';
$db['default']['swap_pre'] = '';
$db['default']['autoinit'] = TRUE;
$db['default']['stricton'] = FALSE;
$db['latestdb']['hostname'] = 'localhost';
$db['latestdb']['username'] = 'root';
$db['latestdb']['password'] = 'pass';
$db['latestdb']['database'] = 'latestdb';
$db['latestdb']['dbdriver'] = 'mysql';
$db['latestdb']['dbprefix'] = '';
$db['latestdb']['pconnect'] = TRUE;
$db['latestdb']['db_debug'] = TRUE;
$db['latestdb']['cache_on'] = FALSE;
$db['latestdb']['cachedir'] = '';
$db['latestdb']['char_set'] = 'utf8';
$db['latestdb']['dbcollat'] = 'utf8_general_ci';
$db['latestdb']['swap_pre'] = '';
$db['latestdb']['autoinit'] = TRUE;
$db['latestdb']['stricton'] = FALSE;
$db['sit']['hostname'] = 'localhost';
$db['sit']['username'] = 'root';
$db['sit']['password'] = 'pass';
$db['sit']['database'] = 'sit';
$db['sit']['dbdriver'] = 'mysql';
$db['sit']['dbprefix'] = '';
$db['sit']['pconnect'] = TRUE;
$db['sit']['db_debug'] = TRUE;
$db['sit']['cache_on'] = FALSE;
$db['sit']['cachedir'] = '';
$db['sit']['char_set'] = 'utf8';
$db['sit']['dbcollat'] = 'utf8_general_ci';
$db['sit']['swap_pre'] = '';
$db['mappsit']['autoinit'] = TRUE;
$db['mappsit']['stricton'] = FALSE;
$db['fold']['hostname'] = 'localhost';
$db['fold']['username'] = 'root';
$db['fold']['password'] = 'pass';
$db['fold']['database'] = 'fold';
$db['fold']['dbdriver'] = 'mysql';
$db['fold']['dbprefix'] = '';
$db['fold']['pconnect'] = TRUE;
$db['fold']['db_debug'] = TRUE;
$db['fold']['cache_on'] = FALSE;
$db['fold']['cachedir'] = '';
$db['fold']['char_set'] = 'utf8';
$db['fold']['dbcollat'] = 'utf8_general_ci';
$db['fold']['swap_pre'] = '';
$db['fold']['autoinit'] = TRUE;
$db['fold']['stricton'] = FALSE;
/* End of file database.php */
/* Location: ./application/config/database.php */我知道错误出在构造函数第$DB2 = $CI->load->database($DB, TRUE);行中，我必须从所选数据库中插入，更新和删除，否则它将使用默认数据库并将其插入。
您可以在每次执行查询时加载数据库，在$ load->数据库（'localhos或Latestdb或sit ...，TRUE）函数中，第一个参数可以是变量或函数。
function myfuntion{
$SomeDataBase = $this->load->database('localhost for example', TRUE);
$result=$SomeDataBase->query('SELECT...');
}