如何将nano.uuid添加到从DB读取的promise链中？

Question

我使用这个代码与快速路由和纳米：

router.get('/', function (request, response) {
  db.view('designdoc', 'bydate', { 'descending': true })
    .then(results => {
      // data manipulation of results, all blocking and fine
      return results;
    })
    .then(results => {
        nano.uuids(1)
          .then(uuids => {
            results.uuid = uiids['uuids'][0];
            resolve(); // return ?
          })
          .catch(error => {
          // ?
           });
      });
      return results;
    })
    .then(results => { response.json(results); }) // how to have results.uuid = something from the previous then ?
    .catch(error => { response.json(error); });

我想从nano.uuid添加一个uuid到结果，但我无法弄清楚如何操纵下一个then内的承诺。

如何从nano.uuid获取数据，等待它并将其添加到results？

edit

我正在转向@ narayansharma91建议的异步方法，这段代码解决了我的问题：

    router.get('/', async function (request, response) {
      const results = await db.view('designdoc', 'bydate', { 'descending': true });
      var uuid = await nano.uuids(1);
      results.uuid = uuid.uuids[0];
      response.json(results);
    }

但我仍然希望了解基于承诺的解决方案。

Answer 1

您不需要执行此长脚本来获取结果。您可以使用async/await执行相同的操作，如下所示。

 router.get('/', async function (request, response) {
     const result = await db.view('designdoc', 'bydate', { 'descending': true })
     console.log(result)//do what ever you want to with result
});

Answer 2

   function successcb(results){
    return new Promise(function(resolve, reject) {
    nano.uuids(1)
  .then(uuids => {
    results.uuid = uiids['uuids'][0];
    resolve(results);
  })
  .catch(error => {
    throw err;
   });
  });
}

router.get('/', function (request, response) {
  db.view('designdoc', 'bydate', { 'descending': true })
    .then(results => {

      return results;
    })
    .then(successcb)
    .then(results => { response.json(results); }) 
    .catch(error => { response.json(error); });

Answer 3

我没有改变你的代码，因为你想要一个承诺的解决方案。您不需要调用resolve（），因为.then（）会为您执行此操作。将uuids附加到结果后，只需返回结果。

router.get('/', function (request, response) {
    db.view('designdoc', 'bydate', {
            'descending': true
        })
        .then(results => {
            // data manipulation of results, all blocking and fine
            return results;
        })
        .then(results => {
            results = nano.uuids(1)
                .then(uuids => {
                    results.uuid = uiids['uuids'][0];
                    return results;
                })
                .catch(error => {
                    throw error;
                });
            return results;
        }).then(results => {
            response.json(results);
        }) // how to have results.uuid = something from the previous then ?
        .catch(error => {
            response.json(error);
        });

})

Answer 4

router.get('/', function(request, response) {
            let _results;
            db.view('designdoc', 'bydate', {
                    'descending': true
                })
                .then(results => {
                    // data manipulation of results, all blocking and fine
                    // save results in tempopary variable
                    // since we want to use only one level of Promise chains
                    // we need to save results on controller scope level to allow access in further chains
                    _results = results;
                    // we don't need to return since every `then` by default return `Promise`
                })
                .then(() => {
                    // you can just return, since nano.uuids return Promise
                    // next then chain will be called once action completed
                    return nano.uuids();
                })
                .then(uuids => {
                    // use _results from controller level scope
                    // uuids will be injected as a result of return nano.uuids()
                    _results.uuid = uiids['uuids'][0];
                    response.json(_results);
                })
                .catch(error => {
                    response.json(error);
                });
        }

为了更好地理解Promise链，我总是建议阅读这个great article