node封装mysql模块

node是基于异步的，所以在进行数据库查询操做的一般是经过回调来操做查询结果。可是在有了es7的async/await，基本再也不须要回调了，因此本篇是基于async/await对mysql进行一次操做封装，让查询更加方便。（node版本需>=7.0）。 

简单来讲，async/await的实现原理是基于promise，根据promise的状态来判断是否真正返回，所以咱们能够在mysql真正查询到结果后将promise状态切换为resolve，返回结果。如出现错误经过reject返回错误信息，reject须要用try/catch进行捕获。

'use strict';
const mysql = require('mysql');
var local = true
var pool

// 建立链接池
if (local) {
    pool = mysql.createPool({
        connectionLimit: 50,
        host: 'localhost',
        user: 'root',
        password: 'root',
        database: 'crawl',
        multipleStatements: true  //是否容许执行多条sql语句
    });
} 

//将结果已对象数组返回
var row = (sql, ...params) => {
    return new Promise(function (resolve, reject) {
        pool.getConnection(function (err, connection) {
            if (err) {
                reject(err);
                return;
            }
            connection.query(sql, params, function (error, res) {
                connection.release();
                if (error) {
                    reject(error);
                    return;
                }
                resolve(res);
            });
        });
    });
};

//返回一个对象
var first = (sql, ...params) => {
    return new Promise(function (resolve, reject) {
        pool.getConnection(function (err, connection) {
            if (err) {
                reject(err);
                return;
            }
            connection.query(sql, params, function (error, res) {
                connection.release();
                if (error) {
                    reject(error);
                    return;
                }
                resolve(res[0] || null);
            });
        });
    });
};

//返回单个查询结果
var single = (sql, ...params) => {
    return new Promise(function (resolve, reject) {
        pool.getConnection(function (err, connection) {
            if (err) {
                reject(err);
                return;
            }
            connection.query(sql, params, function (error, res) {
                connection.release();
                if (error) {
                    reject(error);
                    return;
                }
                for (let i in res[0]) {
                    resolve(res[0][i] || null);
                    return;
                }
                resolve(null);
            });
        });
    });
}

//执行代码，返回执行结果
var execute = (sql, ...params) => {
    return new Promise(function (resolve, reject) {
        // 获取链接
        pool.getConnection(function (err, connection) {
            if (err) {
                reject(err);
                return;
            }
            // 操做数据库
            connection.query(sql, params, function (error, res) {
                // 释放
                connection.release();
                if (error) {
                    reject(error);
                    return;
                }
                resolve(res);
            });
        });
    });
}

//模块导出
module.exports = {
    ROW: row,
    FIRST: first,
    SINGLE: single,
    EXECUTE: execute
}

/*链接mysql*/
function connectToMysql() {
    var connection = mysql.createConnection({
        host: '',
        user: '',
        password: '',
        database: ''
    });
    connection.connect();
    //查询
    connection.query('SELECT * FROM user;', function (err, rows, fields) {
        if (err) throw err;
        console.log('The solution is: ', rows[0]);
    });
    //关闭链接
    connection.end();
}