使用app.get（..）进行路由后，Express JS'this'未定义

I have a basic Node JS server which is designed to be used as an API, I've created a log and database module and I've started adding other modules to deal with different request types.

我有一个基本的Node JS服务器，它被设计用作API，我创建了一个日志和数据库模块，我已经开始添加其他模块来处理不同的请求类型。

I'm using Express.js and node-mysql

我正在使用Express.js和node-mysql

When I visit /v1/group I get the following error -

当我访问/ v1 / group时，我收到以下错误 -

TypeError: Cannot read property 'database' of undefined
    at Group.getAll (C:\code\javascript\node\api\api\v1\groups.js:12:23)
    at callbacks (C:\code\javascript\node\api\node_modules\express\lib\router\index.js:161:37) ...

So I guess after recieving a request and calling group.getAll() that this is undefined but I don't understand why, is there a way to set this or have I structured my application all wrong?

所以我想在收到一个请求并调用group.getAll（）之后，这是未定义但我不明白为什么，有没有办法设置这个或者我的应用程序结构错了？

sever.js

sever.js

"use strict";

var Express = require('express');
var Log = require('./database/log');
var Database = require('./database/database');
var dbConfig = require('./dbconfig.json');

var Group = require('./api/v1/groups');


//Init express
var app = new Express();

//Init log and database
var log = new Log();
var database = new Database(dbConfig, log);

var initCallback = function() {
    //Init routes
    var group = new Group(database, log);

    //Group routes
    app.get('/v1/group', group.getAll);
    app.get('/v1/group/:id', group.getByID);

    app.listen(3000);
    log.logMessage("INFO", "Listening on port 3000");
};

//Test database connection
database.getConnection(function(err, connection) {
    if (err) {
        log.logMessage("FATAL", "Error connecting to database, check database is running and the dbconfig.json file is present and correct.");
        process.exit(1);
    }
    connection.end();

    initCallback();
});

database.js

database.js

"use strict";

var mysql = require('mysql');


var Database = function(dbConfig, log) {
    this.connected = false;
    this.log = log;

    this.log.logMessage("INFO", "Connecting to database with: Host - " + dbConfig.dbhost + ", Database port - " + dbConfig.dbport + ", Database name - " + dbConfig.dbname + ", User " + dbConfig.dbuser + ", Password length - " + dbConfig.dbpass.length);

    this.pool  = mysql.createPool({
        host : dbConfig.dbhost,
        user : dbConfig.dbuser,
        port: dbConfig.dbport,
        password : dbConfig.dbpass,
        database: dbConfig.dbname
    });
};

Database.prototype.getConnection = function() {
    var args = arguments;
    return this.pool.getConnection.apply(this.pool, arguments);
};

module.exports = Database;

groups.js

groups.js

"use strict";

var Group = function(database, log) {
    this.database = database;
    this.log = log;
};

Group.prototype.getAll = function(req, res) {
    console.log(this); // --> undefined

    var query = 'SELECT * FROM invgroups WHERE published = 1';

    this.database.getConnection(function(err, connection) { // --> error line
        if (err) { res.send(500, "Database error"); }

        connection.query(query, function(err, results) {
            if (err) { res.send(500, "Database error"); }
            res.send(results);
        });

        connection.end();
    });

};


Group.prototype.getByID = function(req, res) {
    console.log(this);
    res.send({name: "Group Item 1"});
};

module.exports = Group;

1 个解决方案

#1

You need to properly bind the function.

您需要正确绑定该功能。

app.get('/v1/group', group.getAll);

only passes the getAll function as a handler, but the function itself has no concept of this. this is decided based on the context that is bound, or based on how the function is called. This blog post is useful for understanding how function context works.

只将getAll函数作为处理程序传递，但函数本身没有这个概念。这是根据绑定的上下文或基于函数的调用方式决定的。此博客文章有助于了解函数上下文的工作原理。

app.get('/v1/group', group.getAll.bind(group));