Question

service.js文件中包含以下代码。

exports.getSeminarDetailsById = async function (seminarId) {
try {
    let SeminarList = [];
    var seminarData = await SeminarRepository.getSeminarDetailsById(seminarId);
    if (seminarData && seminarData.length > 0) {
        let userIdList = [...new Set(seminarData.map(x => x.user_id))];
        if (userIdList && userIdList.length > 0) {
            let userDetails = await EmployeeRepository.getEmployeeDetailsByUserIds(userIdList);
            if (userDetails && userDetails.length > 0) {
                seminarData.forEach(element => {
                    let seminarDetail;
                    let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
                    let categoryName;
                    if (element.category_id == 1)
                        categoryName = AppConstants.seminarCategoryName.TECHNICAL;
                    else
                        categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;

                    seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
                    await mapAttachmentWithSeminar(seminarId, seminarDetail);
                    console.log("second", seminarDetail);
                    SeminarList.push(seminarDetail);
                });
            }
        }
    }
    return SeminarList;
} catch (err) {
    console.log(err);
    throw err;
}
}

await mapAttachmentWithSeminar(seminarId, seminarDetail);出现错误，并且在以下相同文件中定义了该错误。

async function mapAttachmentWithSeminar(seminarId, seminarDetail) {
var seminarAttachmentDetails = await SeminarRepository.getSeminarAttachmentDetailsById(seminarId);
  if (seminarAttachmentDetails && seminarAttachmentDetails.length > 0) {
    let AttachmentDetails = [];
    seminarAttachmentDetails.forEach(element => {
        let attachmentDetails = new SeminarAttachmentDetails(element);
        AttachmentDetails.push(attachmentDetails);
    });
    seminarDetail.SeminarAttachmentDetails = AttachmentDetails;
  }
  else {
    seminarDetail.SeminarAttachmentDetails = null;
    console.log("first", seminarDetail);
  }
}

如果我删除了等待功能，那么在执行功能console.log("second", seminarDetail);之前，将首先执行mapAttachmentWithSeminar()。因此，该函数返回的SeminarAttachmentDetails的值将被遗漏，如下所示：

这是预期的输出。

Answer 1

您可以使用经典的.forEach循环来代替for

for(let i = 0; i < seminarData.length; i++){
    let element = seminarData[i];
    let seminarDetail;
    let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
    let categoryName;
    if (element.category_id == 1)
        categoryName = AppConstants.seminarCategoryName.TECHNICAL;
    else
        categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;

    seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
    await mapAttachmentWithSeminar(seminarId, seminarDetail);
    console.log("second", seminarDetail);
    SeminarList.push(seminarDetail);
}

Answer 2

每个嵌套函数以及父函数都应声明为async。如果您在嵌套级别之一中缺少此声明，请注意这部分代码

seminarData.forEach(async element => {
//                  ^^^^ async missed here
 let seminarDetail;
 let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
 let categoryName;
 if (element.category_id == 1)
  categoryName = AppConstants.seminarCategoryName.TECHNICAL;
 else
  categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;
 seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
 await mapAttachmentWithSeminar(seminarId, seminarDetail); 
 console.log("second", seminarDetail); 
 SeminarList.push(seminarDetail);
});

Answer 3

首先，您使用了错误的异步等待。您正在等待非异步功能的范围。在这里：

 seminarData.forEach(element => {
                let seminarDetail;
                let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
                let categoryName;
                if (element.category_id == 1)
                    categoryName = AppConstants.seminarCategoryName.TECHNICAL;
                else
                    categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;

                seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
                await mapAttachmentWithSeminar(seminarId, seminarDetail);
                console.log("second", seminarDetail);
                SeminarList.push(seminarDetail);
            });

你应该有这个

 // here you have the SeminarList but promisified
 // with the form Promise<SeminarListItem>[]
 // to get the values out of the promises you have to await this array     
    const promisifiedSeminarList = seminarData.map((element)=>{
         let userName = userDetails.filter(x => x.user_id == element.user_id).map(
            x => x.userfullname)[0]
         );

        const categoryName = elemenet.category_id == 1
          ? AppConstants.seminarCategoryName.TECHNICAL
          : AppConstants.seminarCategoryName.NONTTECHNICAL;

       const seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
       return mapAttachmentWithSeminar(seminarId, seminarDetail);
    });
  // now
   const seminarList = await Promise.all(promisifiedSeminarList);

为此，您需要mapAttachmentWithSemniar函数返回一个未发生的值

节点Js-SyntaxError：await仅在异步功能中有效

3 个答案: