在 promise 链中调用 express 中间件 next()

Question

我正在尝试构建一个加载请求的参数中间件 object 并将其附加到 request object，这样我就不必一遍又一遍地编写相同的代码。我正在使用 Sequelize 作为 ORM 来访问基于 Promise (bluebird) 的 MySQL 数据库。代码如下：

router.param('id', function (req, res, next, id) {
  return models.Object.findById(id)
    .then((object) => {
      //Check if the requested object was found
      if (object) {
        //Append the request object to the request object
        //for further usage in upcoming route handlers
        req.object = object
        return next()
      } else {
        //Throw an error, so that it can be caught
        //by the catch block of the promise chain
        let err = new Error('Object not found.')
        err.status = 404
        throw err
      }
    })
    //Catch any error and forward it to the
    //next express error handler
    .catch((err) => { return next(err) })
})

如你所见，我正在检查请求的对象是否存在，如果存在，我将其追加到 express 的请求对象中。如果不是，我会抛出一个错误。当我运行此代码时，我收到警告： Warning: a promise was created in a handler at /*path goes here*/ but was not returned from it。在这一点上，我真的不知道如何摆脱那个错误。

编辑：

我尝试了Hosar的解决方案，但不幸的是仍然出现警告。这是我使用的确切代码：

router.param('aId', function (req, res, next, aId) {
  models.Authorization.findById(aId)
    .then((authorization) => {
      if (authorization) {
        req.authorization = authorization
        next()
      } else {
        let err = new Error('Not Found')
        err.status = 404
        next(err)
      }
    })
    .catch((err) => { return next(err) })
})

错误发生在我想调用不带任何参数的next() 的那一行。完整的警告是： (node:5504) Warning: a promise was created in a handler at C:\Users\dkaiser \repos\lead\lead_backend\routes\auth.js:10:16 but was not returned from it

Answer 1

问题是你在return许诺。只需避免使用第一个 return。
尝试：

router.param('id', function (req, res, next, id) {
  models.Object.findById(id)
    .then((object) => {
      //Check if the requested object was found
      if (object) {
        //Append the request object to the request object
        //for further usage in upcoming route handlers
        req.object = object
        next()
      } else {
        //Throw an error, so that it can be caught
        //by the catch block of the promise chain
        let err = new Error('Object not found.')
        err.status = 404
        next(err);
      }
    })
    //Catch any error and forward it to the
    //next express error handler
    .catch((err) => { next(err) })
})

Answer 2

您可以使用 Node v7.6 中的异步中间件功能直接从已解析的 Promise 中提取数据

router.param('id', async function (req, res, next, id) {
  const object = await models.Object.findById(id);
  if (object) {
    req.object = object;
    next();
  } else {
    let err = new Error('Object not found.')
    err.status = 404
    next(err);
  }
 });

在 promise 链中调用 express 中间件 next()

Call express middlewares next() inside a promise chain

javascript

node.js

express

bluebird

编辑：