yii的db解读

1.yii中与数据库连接的时候，是通过ActiveRecord进行连接的，一般需要与数据库表进行对应的类需要继承ActiveRecord，而对于该表中数据库的查询，同样也是在该

User类中定义的查询方法，不同的是，该查询的方法定义是static的。

2. 对于yii与数据库的链接是在配置文件中已经描写过的

<?php
defined('YII_DEBUG') or define('YII_DEBUG', true);
defined('YII_ENV') or define('YII_ENV', 'dev');

require(__DIR__ . '/../../vendor/autoload.php');
require(__DIR__ . '/../../vendor/yiisoft/yii2/Yii.php');
require(__DIR__ . '/../../common/config/bootstrap.php');
require(__DIR__ . '/../config/bootstrap.php');

$config = yii\helpers\ArrayHelper::merge(
    require(__DIR__ . '/../../common/config/main.php'),
    require(__DIR__ . '/../../common/config/main-local.php'),   //我的数据库配置是在这其中的
    require(__DIR__ . '/../config/main.php'),
    require(__DIR__ . '/../config/main-local.php')
);
(new yii\web\Application($config))->run();

3.而对应的common/config/main-local.php文件内容是这样的：

<?php
return [
    'components' => [
        'db' => [
            'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=10.1.20.36;dbname=db_XXX',
            'username' => 'weihu_dev',
            'password' => 'xxxxxx',
            'charset' => 'utf8',
        ],
        'mailer' => [
            'class' => 'yii\swiftmailer\Mailer',
            'viewPath' => '@common/mail',
            // send all mails to a file by default. You have to set
            // 'useFileTransport' to false and configure a transport
            // for the mailer to send real emails.
            'useFileTransport' => true,
        ],
    ],
];

4.整个初始化Yii::$app->db的初始化过程是这样的，整个配置字符是在 main-local.php当中的，而其内容是在$config中的，这个过程是在base/Application中的

public static function configure($object, $properties)
{  
    foreach ($properties as $name => $value) {

        $object->$name = $value;
    }
    return $object;
}
public function setComponents($components)
{
    foreach ($components as $id => $component) {
        $this->set($id, $component);
    }
}
public function set($id, $definition)
{
    if ($definition === null) {
        unset($this->_components[$id], $this->_definitions[$id]);
        return;
    }

    unset($this->_components[$id]);

    if (is_object($definition) || is_callable($definition, true)) {
        // an object, a class name, or a PHP callable
        $this->_definitions[$id] = $definition;
    } elseif (is_array($definition)) {
        // a configuration array
        if (isset($definition['class'])) {
            $this->_definitions[$id] = $definition;
        } else {
            throw new InvalidConfigException("The configuration for the \"$id\" component must contain a \"class\" element.");
        }
    } else {
        throw new InvalidConfigException("Unexpected configuration type for the \"$id\" component: " . gettype($definition));
    }
}
'db' => [
    'class' => 'yii\db\Connection',
    'dsn' => 'mysql:host=db1-dev.bj1.haodf.net;dbname=db_Hdf',
    'username' => 'weihu_dev',
    'password' => '[e-mail]',
    'charset' => 'utf8',
]
public function getDb()
{
    return $this->get('db');
}
public function get($id, $throwException = true)
{

    if (isset($this->_components[$id])) {
        return $this->_components[$id];
    }

    if (isset($this->_definitions[$id])) {
        $definition = $this->_definitions[$id];
        if (is_object($definition) && !$definition instanceof Closure) {
            return $this->_components[$id] = $definition;
        } else {
            return $this->_components[$id] = Yii::createObject($definition);
        }
    } elseif ($throwException) {
        throw new InvalidConfigException("Unknown component ID: $id");
    } else {
        return null;
    }
}