node封裝mysql模塊

node是基於異步的，所以在進行數據庫查詢操做的一般是經過回調來操做查詢結果。可是在有了es7的async/await，基本再也不須要回調了，因此本篇是基於async/await對mysql進行一次操做封裝，讓查詢更加方便。（node版本需>=7.0）。 

簡單來講，async/await的實現原理是基於promise，根據promise的狀態來判斷是否真正返回，所以咱們能夠在mysql真正查詢到結果後將promise狀態切換爲resolve，返回結果。如出現錯誤經過reject返回錯誤信息，reject須要用try/catch進行捕獲。

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

// 建立鏈接池
if (local) {
    pool = mysql.createPool({
        connectionLimit: 50,
        host: 'localhost',
        user: 'root',
        password: 'root',
        database: 'crawl',
        multipleStatements: true  //是否容許執行多條sql語句
    });
} 

//將結果已對象數組返回
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);
            });
        });
    });
};

//返回一個對象
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);
            });
        });
    });
};

//返回單個查詢結果
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);
            });
        });
    });
}

//執行代碼，返回執行結果
var execute = (sql, ...params) => {
    return new Promise(function (resolve, reject) {
        // 獲取鏈接
        pool.getConnection(function (err, connection) {
            if (err) {
                reject(err);
                return;
            }
            // 操做數據庫
            connection.query(sql, params, function (error, res) {
                // 釋放
                connection.release();
                if (error) {
                    reject(error);
                    return;
                }
                resolve(res);
            });
        });
    });
}

//模塊導出
module.exports = {
    ROW: row,
    FIRST: first,
    SINGLE: single,
    EXECUTE: execute
}

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