問(wèn)題描述

最后用了promise解決，代碼如下：exports.selectByUsername = selectByUsername;function selectByUsername(username){

var promise = new Promise(function(resolve){ var sql = 'SELECT COUNT(*) count FROM wx_user WHERE username = ?'; var sqlParams = [username]; var count; co.query(sql,sqlParams,function(err,result){if(err){ return console.log(err.message);}console.log('------------------------開(kāi)始查詢---------------------');console.log(result);var str = JSON.stringify(result);var json = JSON.parse(str);count = json[0].count;console.log(count);console.log('------------------------查詢結(jié)束---------------------');resolve(count); });});promise.then(function(value){ // console.log(value); return value;});return promise;

}

app.post(’/ajax’,urlencodedParser,function(req,res){

username = req.body.name;console.log(username);var promise = s.selectByUsername(username);promise.then(function(value){ console.log(value); if(value!==1){res.send('用戶名不存在'); }});

});

參考文檔：http://liubin.org/promises-book/

問(wèn)題解答

query里面的function在query完成后才會(huì)執(zhí)行到，而這個(gè)時(shí)候外部函數(shù)已經(jīng)返回了，所以count不會(huì)賦到值，仍然為undefined

寫(xiě)在query里也不會(huì)返回count的，因?yàn)閝uery這個(gè)方法是異步的

簡(jiǎn)而言之，把return count 寫(xiě)在query 里面就好了。