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HomeDatabaseMysql Tutorial在异步回调中操作redis的一个异常

在异步回调中操作redis的一个异常

Jun 07, 2016 pm 04:38 PM
redisusecallbackabnormalasynchronousoperateyesterday

昨天在使用node redis的时候报了这样一个错: TypeError: Object [object Object] has no method 'send_command' at RedisClient.(anonymous function) (D:\index.js:991:25) at null._onTimeout (D:\index.js:17:22) at Timer.listOnTimeout [as ontimeout]

昨天在使用node redis的时候报了这样一个错:

TypeError: Object [object Object] has no method 'send_command'
    at RedisClient.(anonymous function) (D:\index.js:991:25)
    at null._onTimeout (D:\index.js:17:22)
    at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)

这个bug比较隐蔽,一步一步来看:

起因

我要实现的是批量插入redis的列表(list),相关的api是这样的:client.rpush(key, [value1, value2, ..., callback]) ,参数必须一个一个列出来,要想批量添加(数组),只能使用apply 方法了:

var array = ['list', '1', '2', '3', '4',
    function() {
        console.log('success');
    }
];
client.rpush.apply(this, array);

数组的第一参数是key,最后一个是回调函数,之间全部是要添加的数据。构造这样一个数组,使用apply 就很完美的解决了批量添加的问题。但是还是太年轻啊,执行demo的时候很正常,但是放入正式代码中就有问题了。

解决

正式代码的数据一般是异步得到的,用setTimeout 模拟一下:

var redis = require('redis'),
    client = redis.createClient(6379, '127.0.0.1', {
        auth_pass: 'home.local.17173.com'
    });
client.on('error', function(err) {
    console.log('redis错误:' + err);
});
client.on('connect', function() {
    setTimeout(function() {
        var array = ['list', '1', '2', '3', '4',
            function() {
                console.log('success');
            }
        ];
        client.rpush.apply(this, array);
    }, 1000);
});

执行上面的代码会报出文章开头的错误,提示“Object [object Object] has no method ‘send_command’”,联系到apply 的this,问题可能出在作用域上,修改倒数第三行代码:

client.rpush.apply(client, array);

执行后就ok了:

所以问题就是出在作用域上,apply 这样的比较明显,但是使用async等就不是那么明显了。在stackoverflow上找到一个问题,有bug的代码是这样的:

var async = require('async');
var redis = require('redis');
var keys = ['key1', 'key2', 'key3'];
var client = redis.createClient();
var multi = client.multi();
for (var key in keys) {
  multi.hmset(key, {'some': 'value'});
}
multi.exec(function(err, res) {
  if (err) throw err;
  console.dir(res);
  var myCallback = function(err, res) {
    console.log('in myCallback');
    console.dir(res);
    client.quit();
    process.exit();
  };
 async.concat(keys, client.hgetall, myCallback);
});

错误还是和文章开头的一样,解决方法是使用bind 函数。修改倒数第二行代码如下:

async.concat(keys, client.hgetall.bind(client), myCallback);

bind函数可以用来设置this 参数,具体用法看这里。

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