Database Exception – yii\db\Exception

     * Returns the PDO instance for the currently active master connection.
     * This method will open the master DB connection and then return [[pdo]].
     * @return PDO the PDO instance for the currently active master connection.
     */
    public function getMasterPdo()
    {
        $this->open();
        return $this->pdo;
    }
 
    /**
     * Returns the currently active slave connection.
     * If this method is called for the first time, it will try to open a slave connection when [[enableSlaves]] is true.

     * is available and `$fallbackToMaster` is false.
     */
    public function getSlavePdo($fallbackToMaster = true)
    {
        $db = $this->getSlave(false);
        if ($db === null) {
            return $fallbackToMaster ? $this->getMasterPdo() : null;
        }
 
        return $db->pdo;
    }
 
    /**

     *
     * @return bool
     * @see https://dev.mysql.com/doc/refman/5.6/en/fractional-seconds.html
     */
    private function supportsFractionalSeconds()
    {
        $version = $this->db->getSlavePdo()->getAttribute(\PDO::ATTR_SERVER_VERSION);
        return version_compare($version, '5.6.4', '>=');
    }
 
    /**
     * Returns the map for default time type.
     * If the version of MySQL is lower than 5.6.4, then the types will be without fractional seconds,

        $map = [
            Schema::TYPE_DATETIME => 'datetime',
            Schema::TYPE_TIMESTAMP => 'timestamp',
            Schema::TYPE_TIME => 'time',
        ];
 
        if ($this->supportsFractionalSeconds()) {
            $map = [
                Schema::TYPE_DATETIME => 'datetime(0)',
                Schema::TYPE_TIMESTAMP => 'timestamp(0)',
                Schema::TYPE_TIME => 'time(0)',
            ];
        }

     * {@inheritdoc}
     */
    public function init()
    {
        parent::init();
 
        $this->typeMap = array_merge($this->typeMap, $this->defaultTimeTypeMap());
    }
 
    /**
     * {@inheritdoc}
     */
    protected function defaultExpressionBuilders()

     */
    public function __construct($config = [])
    {
        if (!empty($config)) {
            Yii::configure($this, $config);
        }
        $this->init();
    }
 
    /**
     * Initializes the object.
     * This method is invoked at the end of the constructor after the object is initialized with the
     * given configuration.

     * @param Connection $connection the database connection.
     * @param array $config name-value pairs that will be used to initialize the object properties
     */
    public function __construct($connection, $config = [])
    {
        $this->db = $connection;
        parent::__construct($config);
    }
 
    /**
     * {@inheritdoc}
     */
    public function init()

    /**
     * Creates a query builder for the MySQL database.
     * @return QueryBuilder query builder instance
     */
    public function createQueryBuilder()
    {
        return new QueryBuilder($this->db);
    }
 
    /**
     * Resolves the table name and schema name (if any).
     * @param TableSchema $table the table metadata object
     * @param string $name the table name

    /**
     * @return QueryBuilder the query builder for this connection.
     */
    public function getQueryBuilder()
    {
        if ($this->_builder === null) {
            $this->_builder = $this->createQueryBuilder();
        }
 
        return $this->_builder;
    }
 
    /**

    /**
     * Returns the query builder for the current DB connection.
     * @return QueryBuilder the query builder for the current DB connection.
     */
    public function getQueryBuilder()
    {
        return $this->getSchema()->getQueryBuilder();
    }
 
    /**
     * Can be used to set [[QueryBuilder]] configuration via Connection configuration array.
     *
     * @param array $value the [[QueryBuilder]] properties to be configured.

        $modelClass = $this->modelClass;
        if ($db === null) {
            $db = $modelClass::getDb();
        }
 
        if ($this->sql === null) {
            list($sql, $params) = $db->getQueryBuilder()->build($this);
        } else {
            $sql = $this->sql;
            $params = $this->params;
        }
 
        $command = $db->createCommand($sql, $params);

    public function one($db = null)
    {
        if ($this->emulateExecution) {
            return false;
        }
 
        return $this->createCommand($db)->queryOne();
    }
 
    /**
     * Returns the query result as a scalar value.
     * The value returned will be the first column in the first row of the query results.
     * @param Connection $db the database connection used to generate the SQL statement.

     * @return ActiveRecord|array|null a single row of query result. Depending on the setting of [[asArray]],
     * the query result may be either an array or an ActiveRecord object. `null` will be returned
     * if the query results in nothing.
     */
    public function one($db = null)
    {
        $row = parent::one($db);
        if ($row !== false) {
            $models = $this->populate([$row]);
            return reset($models) ?: null;
        }
 
        return null;

                break;
            }
        }
 
        $result = null;
 
        if ($runAction && $this->beforeAction($action)) {
            // run the action
            $result = $action->runWithParams($params);
 
            $result = $this->afterAction($action, $result);
 
            // call afterAction on modules

        $parts = $this->createController($route);
        if (is_array($parts)) {
            /* @var $controller Controller */
            list($controller, $actionID) = $parts;
            $oldController = Yii::$app->controller;
            Yii::$app->controller = $controller;
            $result = $controller->runAction($actionID, $params);
            if ($oldController !== null) {
                Yii::$app->controller = $oldController;
            }
 
            return $result;
        }

            $params = $this->catchAll;
            unset($params[0]);
        }
        try {
            Yii::debug("Route requested: '$route'", __METHOD__);
            $this->requestedRoute = $route;
            $result = $this->runAction($route, $params);
            if ($result instanceof Response) {
                return $result;
            }
 
            $response = $this->getResponse();
            if ($result !== null) {

    {
        try {
            $this->state = self::STATE_BEFORE_REQUEST;
            $this->trigger(self::EVENT_BEFORE_REQUEST);
 
            $this->state = self::STATE_HANDLING_REQUEST;
            $response = $this->handleRequest($this->getRequest());
 
            $this->state = self::STATE_AFTER_REQUEST;
            $this->trigger(self::EVENT_AFTER_REQUEST);
 
            $this->state = self::STATE_SENDING_RESPONSE;
            $response->send();