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;
        } else {
            return $db->pdo;
        }
    }
 
    /**

 
        if ($this->db->getTransaction()) {
            // master is in a transaction. use the same connection.
            $forRead = false;
        }
        if ($forRead || $forRead === null && $this->db->getSchema()->isReadQuery($sql)) {
            $pdo = $this->db->getSlavePdo();
        } else {
            $pdo = $this->db->getMasterPdo();
        }
 
        try {
            $this->pdoStatement = $pdo->prepare($sql);

                    Yii::trace('Query result served from cache', 'yii\db\Command::query');
                    return $result[0];
                }
            }
        }
 
        $this->prepare(true);
 
        $token = $rawSql;
        try {
            Yii::beginProfile($token, 'yii\db\Command::query');
 
            $this->pdoStatement->execute();

     * @return array all rows of the query result. Each array element is an array representing a row of data.
     * An empty array is returned if the query results in nothing.
     * @throws Exception execution failed
     */
    public function queryAll($fetchMode = null)
    {
        return $this->queryInternal('fetchAll', $fetchMode);
    }
 
    /**
     * Executes the SQL statement and returns the first row of the result.
     * This method is best used when only the first row of result is needed for a query.
     * @param int $fetchMode the result fetch mode. Please refer to [PHP manual](http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php)

     * @throws \Exception if DB query fails
     */
    protected function findColumns($table)
    {
        $sql = 'SHOW FULL COLUMNS FROM ' . $this->quoteTableName($table->fullName);
        try {
            $columns = $this->db->createCommand($sql)->queryAll();
        } catch (\Exception $e) {
            $previous = $e->getPrevious();
            if ($previous instanceof \PDOException && strpos($previous->getMessage(), 'SQLSTATE[42S02') !== false) {
                // table does not exist
                // https://dev.mysql.com/doc/refman/5.5/en/error-messages-server.html#error_er_bad_table_error
                return false;

     */
    protected function loadTableSchema($name)
    {
        $table = new TableSchema;
        $this->resolveTableNames($table, $name);
 
        if ($this->findColumns($table)) {
            $this->findConstraints($table);
 
            return $table;
        } else {
            return null;
        }

                }
 
                return $this->_tables[$name];
            }
        }
 
        return $this->_tables[$name] = $this->loadTableSchema($realName);
    }
 
    /**
     * Returns the cache key for the specified table name.
     * @param string $name the table name
     * @return mixed the cache key

     * @throws InvalidConfigException if the table for the AR class does not exist.
     */
    public static function getTableSchema()
    {
        $tableSchema = static::getDb()
            ->getSchema()
            ->getTableSchema(static::tableName());
 
        if ($tableSchema === null) {
            throw new InvalidConfigException('The table does not exist: ' . static::tableName());
        }
 
        return $tableSchema;

     * Note that an array should be returned even for a table with single primary key.
     *
     * @return string[] the primary keys of the associated database table.
     */
    public static function primaryKey()
    {
        return static::getTableSchema()->primaryKey;
    }
 
    /**
     * Returns the list of all attribute names of the model.
     * The default implementation will return all column names of the table associated with this AR class.
     * @return array list of attribute names.

    protected static function findByCondition($condition)
    {
        $query = static::find();
 
        if (!ArrayHelper::isAssociative($condition)) {
            // query by primary key
            $primaryKey = static::primaryKey();
            if (isset($primaryKey[0])) {
                $pk = $primaryKey[0];
                if (!empty($query->join) || !empty($query->joinWith)) {
                    $pk = static::tableName() . '.' . $pk;
                }
                $condition = [$pk => $condition];

    /**
     * @inheritdoc
     * @return static ActiveRecord instance matching the condition, or `null` if nothing matches.
     */
    public static function findOne($condition)
    {
        return static::findByCondition($condition)->one();
    }
 
    /**
     * @inheritdoc
     * @return static[] an array of ActiveRecord instances, or an empty array if nothing matches.
     */

        $args = $this->controller->bindActionParams($this, $params);
        Yii::trace('Running action: ' . get_class($this->controller) . '::' . $this->actionMethod . '()', __METHOD__);
        if (Yii::$app->requestedParams === null) {
            Yii::$app->requestedParams = $args;
        }
 
        return call_user_func_array([$this->controller, $this->actionMethod], $args);
    }
}

        }
 
        $result = null;
 
        if ($runAction && $this->beforeAction($action)) {
            // run the action
            $result = $action->runWithParams($params);
 
            $result = $this->afterAction($action, $result);
 
            // call afterAction on modules
            foreach ($modules as $module) {
                /* @var $module Module */

        $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::trace("Route requested: '$route'", __METHOD__);
            $this->requestedRoute = $route;
            $result = $this->runAction($route, $params);
            if ($result instanceof Response) {
                return $result;
            } else {
                $response = $this->getResponse();
                if ($result !== null) {
                    $response->data = $result;

        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();