[
  'components' => [
    'db'   => [
      'class'     => 'yii\db\Connection',
      'dsn'      => 'mysql:host=localhost;dbname=yii',
      'username'   => 'root',
      'password'   => 'xxxxxx',
      'charset'    => 'utf8'
    ],
    'session' => [
      'class' => 'yii\web\DbSession', //session 操作对象
      'db'  => 'db',   //指定数据库操作组件是上面的组件db
      'sessionTable' => 'yii_session' //session 数据库表名称
    ]
  ]
]

CREATE TABLE yii_session
(
  id CHAR(40) NOT NULL PRIMARY KEY,
  expire INTEGER,
  data BLOB
)

namespace app\controllers\home;
use Yii;
use yii\web\Controller;
class IndexController
{
  public function actionIndex()
  {
    $session = Yii::$app->session;
    if(isset($session['name']) && isset($session['tel']))
    {
      var_dump($session);
    }else{
      $session['name'] = '谭勇';
      $session['tel'] = 22;
      echo 'set session';
    }
  }
}