Question

我正在使用运行Express的Node.js / TypeScript创建API。以下是我的get方法的摘录。格式化方法中会触发错误，该方法会抛出promise所捕获的错误，但不会在抛出后传播到父承诺：

            this.getModel(objectName).findAll(queryParameters).then(function(databaseObjects) {
                for (let databaseObject of databaseObjects) {
                    var jsonObject = {};
                    //console.log("Database object: ");
                    //console.log(databaseObject);
                    transform.baseFormat(databaseObject, jsonObject)
                    .then(() => transform.format(databaseObject, jsonObject))
                    .then(() => {
                        res.locals.retval.addData(jsonObject);
                    }).catch((e) => {
                        console.log("Caught error during format of existing object: ");
                        console.log(e);
                        throw e;
                    });
                }
            })
            .then(() => {
                if (metadata) {
                    this.metadata(objectName, false, transform, res.locals.retval);

                    delete queryParameters.limit;
                    delete queryParameters.offset;
                    console.log("RUNNING METADATA COUNT: ");
                    this.getModel(objectName).count(queryParameters).then(function(count) {
                        res.locals.retval.setMetadata("records", count);
                        return next();
                    }).catch(function(e) {
                        this.error(e, res);
                        return next();
                    });
                } else {
                    console.log("NO METADATA");
                    return next();
                }
            })
            .catch((e) => {
                // TODO: Move status into error() function
                console.log("500 Error on GET");
                console.error(e);
                res.locals.retval.addError(ErrorCode.InternalError, e);
                res.status(ErrorCode.InternalError).send(res.locals.retval);
                return next();
            });

这是输出：

(node:8277) Warning: a promise was created in a handler at /Library/WebServer/adstudio/dist/server.js:555:51 but was not returned from it, see
at Function.Promise.bind (/Library/WebServer/adstudio/node_modules/bluebird/js/release/bind.js:65:20)
Caught error during format of existing object: 
Test Error
END FUNCTION HAS BEEN REACHED!

然后请求无法完成。

我在Promises上阅读了很多内容，但我找不到类似于我的问题/解决方案。

Answer 1

在for循环中运行不是异步的，所以你的承诺基本上在循环结束后立即解决，但在所有格式化完成之前。

使用承诺控制流程，例如bluebird的Promise.each，它是串行的，只是Promise.all。然后会抓住任何例外。

this.getModel(objectName).findAll(queryParameters).then(function (databaseObjects) {
  var promises = databaseObjects.map(databaseObject => {
    var jsonObject = {}
          // console.log("Database object: ");
          // console.log(databaseObject);
    return transform.baseFormat(databaseObject, jsonObject)
          .then(() => transform.format(databaseObject, jsonObject))
          .then(() => {
            res.locals.retval.addData(jsonObject)
          }).catch((e) => {
            console.log('Caught error during format of existing object: ')
            console.log(e)
            throw e
          })
  })
  return Promise.all(promises)
})
.catch((e) => {
    // TODO: Move status into error() function
  console.log('500 Error on GET')
  console.error(e)
  res.locals.retval.addError(ErrorCode.InternalError, e)
  res.status(ErrorCode.InternalError).send(res.locals.retval)
  return next()
})

嵌套Promise不会将错误传播到Node.js中的父Promise？

1 个答案: