Question

我试图获取我保存在neo4j数据库中的idsFromMongo并在mongodb中搜索那些id以返回我想要的对象。它工作一次，但后来我的服务器崩溃，它返回错误无法在发送后设置标题。

这是我的代码：。

routes.get('/advertisements/recommended/:brand', function(req, res) {
  res.contentType('application/json');

  var brandFromUrl = req.params.brand;
  var advertisementIds = [];

  Advertisement.find({'car.brand': brandFromUrl})
    .then(function (ads) {
      // res.status(200).json(ads);
      ads.forEach(function (record) {
        console.log('ids: ' + record._id)
        session
          .run("MERGE(a:Advertisement {idFromMongo: {idParam}, brand: {brandParam}}) WITH a MATCH(b: Advertisement {brand: {brandParam}}) MERGE(a)-[:SHARED_BRAND]->(b)", {idParam: record._id.toString(), brandParam: brandFromUrl})
          .then(function(result) {
            session
              .run("MATCH (n:Advertisement{brand: {brandParam}}) RETURN (n)", {brandParam: brandFromUrl})
              .then(function(result) {
                result.records.forEach(function(record){
                  advertisementIds.push(record._fields[0].properties.idFromMongo);
                });
                Advertisement.find({
                  '_id': { $in: advertisementIds}
                }, function(err, docs){
                  res.status(200).json(docs);
                })
            })
        })
      });
    })
    .catch((error) => {
      res.status(400).json(error);
    });
});

这是我的错误：

Error: Can't set headers after they are sent.
    at validateHeader (_http_outgoing.js:494:11)
    at ServerResponse.setHeader (_http_outgoing.js:501:3)
    at ServerResponse.header (c:\dev\individueel-project\individueel-database\node_modules\express\lib\response.js:767:10)
    at ServerResponse.send (c:\dev\individueel-project\individueel-database\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (c:\dev\individueel-project\individueel-database\node_modules\express\lib\response.js:267:15)
    at c:\dev\individueel-project\individueel-database\api\advertisement.routes.v1.js:70:35
    at model.Query.<anonymous> (c:\dev\individueel-project\individueel-database\node_modules\mongoose\lib\model.js:4046:16)
    at c:\dev\individueel-project\individueel-database\node_modules\kareem\index.js:273:21
    at c:\dev\individueel-project\individueel-database\node_modules\kareem\index.js:131:16
    at _combinedTickCallback (internal/process/next_tick.js:131:7)
    at process._tickCallback (internal/process/next_tick.js:180:9)

Answer 1

这里的问题是你正在执行一个数组并进入你发送响应的数组。因此，最终它会多次发送响应，但只有第一次才会起作用，之后会产生错误。要解决它，你应该在所有promises到数组完成后（Promise.all）回答请求，或者如果你不需要等到整个数组完成，检查你是否已经响应并且不执行它试。

设置后无法设置标题

1 个答案: