Koa js：错误：发送后无法设置标题。 mongoDB

Question

我使用Koa 2的异步函数。

我收到以下错误消息。

events.js:163 1:56 PM throw er; // Unhandled 'error' event 1:56 PM ^ 1:56 PM 1:56 PM Error: Can't set headers after they are sent. 1:56 PM at ServerResponse.setHeader (_http_outgoing.js:371:11) 1:56 PM at Object.set (/app/node_modules/koa/lib/response.js:440:16) 1:56 PM at Object.redirect (/app/node_modules/koa/lib/response.js:261:10) 1:56 PM at Object.proto.(anonymous function) [as redirect] (/app/node_modules/delegates/index.js:40:31) 1:56 PM Jump to at url.findOne (/app/server.js:126:9) 1:56 PM at model.Query. (/app/node_modules/mongoose/lib/model.js:3737:16) 1:56 PM at /app/node_modules/kareem/index.js:277:21 1:56 PM at /app/node_modules/kareem/index.js:131:16 1:56 PM at _combinedTickCallback (internal/process/next_tick.js:73:7) 1:56 PM at process._tickCallback (internal/process/next_tick.js:104:9) 1:56 PM 6 minutes ago

这是我的代码部分。

async function red(ctx) { 
    let redurl = "//url here"; 
    url.findOne({ shortenedLink: redurl }, (err, data) => { 
    //find if short url matches long url in db 
    if (err) throw err; 
    if (data) { 
     //if matches then redirect to long url 
     ctx.redirect(data.url); //getting the error here 
     console.log("matched"); 
    } else console.error("--"); 
    }); 
} 

我完整的代码可以发现here。

Answer 1

如果您使用的是async功能，则应该按照async /`等待？模式和不使用回调。所以，你应该重写你的电话一样：

async function red(ctx) { 
    let redurl = "//url here"; 
    try { 
     data = await url.findOne({ shortenedLink: redurl }) 
     if (data) { 
     ctx.redirect(data.url); //getting the error here 
     console.log("matched"); 
     } else { 
     console.error("--"); 
     } 
    } catch (err) { 
     throw err; 
    } 
} 

Answer 2

我有同样的问题，为我所用链sendStatus功能在我的代码之前。

Country.count({ name: name }, (error, count) => { 
     if (count > 0) { 
      console.log(count); 
      error = name + alreadyExists; 
      res.sendStatus(500).sendStatus(500); 
     } 
}); 

删除多余的sendStatus解决了我的问题。

Country.count({ name: name }, (error, count) => { 
     if (count > 0) { 
      console.log(count); 
      error = name + alreadyExists; 
      res.sendStatus(500); 
     } 
});