Yii2.0 API改造（返回数据库对应字段数据类型）

【改造背景】

使用Yii2.0开发api时，使用asArray()函数时，框架本身默认将所有数据类型都转换成字符串处理。在与前端强类型语言交互时极不方便。所以希望改造框架返回数据表对应字段类型，而无需每次手工进行转换。

【改造步骤】

1、数据库连接配置attributes中增加两个PDO参数：

return [
    'class' => 'commonextConnectionExt', // 这里使用自定义数据库连接拓展类
    'dsn' => 'mysql:host=127.0.0.1;dbname=test',
    'username' => 'root',
    'password' => '123456',
    'charset' => 'utf8mb4',
    'enableSchemaCache' => true,
    'schemaCacheDuration' => 60,
    'enableLogging' => true,
    'commandClass' => 'commonextCommandExt',
    'attributes'  => [
        PDO::ATTR_STRINGIFY_FETCHES => false,
        PDO::ATTR_EMULATE_PREPARES  => false,
    ]
];

2、Yii2.0 （use version：2.0.31）嵌套事务改造：

　　重要说明：因为增加了上面两个PDO参数后，Yii2.0的原有嵌套事务执行会报错，主要原因是框架本身的嵌套事务依赖于模拟预处理。所以还需要下面的改造处理。

　　继承覆写原有的数据库连接类yiidbConnection：

<?php

namespace commonext;

use yiidbConnection;

/**
 * 数据库连接拓展类
 *
 * Class ConnectionExt
 * @package commonext
 */
class ConnectionExt extends Connection
{
    /**
     * @var Transaction the currently active transaction
     */
    private $_transaction;


    /**
     * Returns the currently active transaction.
     * @return Transaction|null the currently active transaction. Null if no active transaction.
     */
    public function getTransaction()
    {
        return $this->_transaction && $this->_transaction->getIsActive() ? $this->_transaction : null;
    }

    /**
     * Starts a transaction.
     * @param string|null $isolationLevel The isolation level to use for this transaction.
     * See [[Transaction::begin()]] for details.
     * @throws
     * @return Transaction the transaction initiated
     */
    public function beginTransaction($isolationLevel = null)
    {
        $this->open();

        if (($transaction = $this->getTransaction()) === null) {
            $transaction = $this->_transaction = new TransactionExt(['db' => $this]); // 这里实例新的事务类
        }
        $transaction->begin($isolationLevel);

        return $transaction;
    }
}

　　继承覆写事务处理类yiidbTransaction：

<?php

namespace commonext;

use Yii;
use yiiaseInvalidConfigException;
use yiiaseNotSupportedException;
use yiidbConnection;
use yiidbException;
use yiidbTransaction;

/**
 * 事务拓展类
 *
 * Class TransactionExt
 * @package commonext
 */
class TransactionExt extends Transaction
{
    /**
     * @var int the nesting level of the transaction. 0 means the outermost level.
     */
    private $_level = 0;


    /**
     * Returns a value indicating whether this transaction is active.
     * @return bool whether this transaction is active. Only an active transaction
     * can [[commit()]] or [[rollBack()]].
     */
    public function getIsActive()
    {
        return $this->_level > 0 && $this->db && $this->db->isActive;
    }

    /**
     * 覆写开始事务method
     *
     * @param string|null $isolationLevel The [isolation level][] to use for this transaction.
     * This can be one of [[READ_UNCOMMITTED]], [[READ_COMMITTED]], [[REPEATABLE_READ]] and [[SERIALIZABLE]] but
     * also a string containing DBMS specific syntax to be used after `SET TRANSACTION ISOLATION LEVEL`.
     * If not specified (`null`) the isolation level will not be set explicitly and the DBMS default will be used.
     *
     * > Note: This setting does not work for PostgreSQL, where setting the isolation level before the transaction
     * has no effect. You have to call [[setIsolationLevel()]] in this case after the transaction has started.
     *
     * > Note: Some DBMS allow setting of the isolation level only for the whole connection so subsequent transactions
     * may get the same isolation level even if you did not specify any. When using this feature
     * you may need to set the isolation level for all transactions explicitly to avoid conflicting settings.
     * At the time of this writing affected DBMS are MSSQL and SQLite.
     *
     * [isolation level]: http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels
     *
     * Starting from version 2.0.16, this method throws exception when beginning nested transaction and underlying DBMS
     * does not support savepoints.
     * @throws InvalidConfigException if [[db]] is `null`
     * @throws NotSupportedException if the DBMS does not support nested transactions
     * @throws Exception if DB connection fails
     */
    public function begin($isolationLevel = null)
    {
        if ($this->db === null) {
            throw new InvalidConfigException('Transaction::db must be set.');
        }
        $this->db->open();

        if ($this->_level === 0) {
            if ($isolationLevel !== null) {
                $this->db->getSchema()->setTransactionIsolationLevel($isolationLevel);
            }
            Yii::debug('Begin transaction' . ($isolationLevel ? ' with isolation level ' . $isolationLevel : ''), __METHOD__);

            $this->db->trigger(Connection::EVENT_BEGIN_TRANSACTION);
            $this->db->pdo->beginTransaction();
            $this->_level = 1;

            return;
        }

        $schema = $this->db->getSchema();
        if ($schema->supportsSavepoint()) {
            Yii::debug('Set savepoint ' . $this->_level, __METHOD__);
            // Notice: solute error: SQLSTATE[HY000]: General error: 2014 Cannot execute queries while other unbuffered queries are active
            $this->db->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
            $schema->createSavepoint('LEVEL' . $this->_level);
            $this->db->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
        } else {
            Yii::info('Transaction not started: nested transaction not supported', __METHOD__);
            throw new NotSupportedException('Transaction not started: nested transaction not supported.');
        }
        $this->_level++;
    }

    /**
     * 覆写提交事务method
     *
     * Commits a transaction.
     * @throws Exception
     */
    public function commit()
    {
        if (!$this->getIsActive()) {
            throw new Exception('Failed to commit transaction: transaction was inactive.');
        }

        $this->_level--;
        if ($this->_level === 0) {
            Yii::debug('Commit transaction', __METHOD__);
            $this->db->pdo->commit();
            $this->db->trigger(Connection::EVENT_COMMIT_TRANSACTION);
            return;
        }

        $schema = $this->db->getSchema();
        if ($schema->supportsSavepoint()) {
            Yii::debug('Release savepoint ' . $this->_level, __METHOD__);
            $this->db->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
            $schema->releaseSavepoint('LEVEL' . $this->_level);
            $this->db->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
        } else {
            Yii::info('Transaction not committed: nested transaction not supported', __METHOD__);
        }
    }

    /**
     * 覆写回滚事务method
     *
     * Rolls back a transaction.
     */
    public function rollBack()
    {
        if (!$this->getIsActive()) {
            // do nothing if transaction is not active: this could be the transaction is committed
            // but the event handler to "commitTransaction" throw an exception
            return;
        }

        $this->_level--;
        if ($this->_level === 0) {
            Yii::debug('Roll back transaction', __METHOD__);
            $this->db->pdo->rollBack();
            $this->db->trigger(Connection::EVENT_ROLLBACK_TRANSACTION);
            return;
        }

        $schema = $this->db->getSchema();
        if ($schema->supportsSavepoint()) {
            Yii::debug('Roll back to savepoint ' . $this->_level, __METHOD__);
            $this->db->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
            $schema->rollBackSavepoint('LEVEL' . $this->_level);
            $this->db->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
        } else {
            Yii::info('Transaction not rolled back: nested transaction not supported', __METHOD__);
        }
    }
}

【补充说明】

1、PDO相关参数说明：

array(
        // 强制 PDO 获取的表字段字符的大小写转换，或原样使用列信息
        PDO::ATTR_CASE              => PDO::CASE_LOWER,
        // 执行出错时抛出异常
        PDO::ATTR_ERRMODE           => PDO::ERRMODE_EXCEPTION,
        //  将返回的空字符串转换为 SQL 的 NULL
        PDO::ATTR_ORACLE_NULLS      => PDO::NULL_NATURAL,
        // 返回数据的时候不将数值转换为字符串
        PDO::ATTR_STRINGIFY_FETCHES => false,
        // 设置为false禁止PDO模拟预处理语句，而使用真正的预处理语句，即有MySQL执行预处理语句
        PDO::ATTR_EMULATE_PREPARES  => false,
    ));

 2、此api改造不受框架对数据类型的处理，参考文章：https://www.cnblogs.com/itsharehome/p/12275979.html