asynchronous - 在 foreach 循环中，等待不起作用

Question

在此代码下方下载controller.js

// Retrieve all downloads from the database.
exports.findAll = async (req, res) => {
  downloadObj
  .findAll(
    {  
      include: [
        {
            model: composerObj,
            required: false,
        },
        {
            model: raagaObj,
            required: false,
        },
        {
            model: taalaObj,
            required: false,
        },
      ],
      where: req.query,
      raw:true,
      nest: true,     
    })
    .then((data) => {
      
    data.forEach(async (element) => {
        const artistsArray = [];
        let whereConstraint = {};
        JSON.parse(element.artists).forEach( async (ele) => { 
          artistsArray.push(ele.artistId);
        });;
        whereConstraint = {
          id : {
            [Op.in]: artistsArray
          }
        }
        element.Active = "true11";
        const artistData =  artistService.customfindAll(whereConstraint);
        element.artistData = artistData;
        console.log("artistData",artistData); 
    });
      
      console.log("data",data);
      console.log("3");

       res.status(200).send({
         status:200,
         message: "ok",
         data:data
       });
       
       console.log("4");
    })
    .catch((err) => {
      res.status(500).send({
        status:500,
        message:
          err.message || "Some error occurred while retrieving Download.",
      });
    });
};

在此代码下方，artistServer.js 文件

exports.customfindAll = async (whereConstraint) => {
    return new Promise(function(resolve, reject) {
        artistObj
        .findAll({ 
          attributes:{  
            include: [
                  [fn('IF',literal('imagePath!=""'),(fn('CONCAT', artistImagePath, 'artist/', col('imagePath'))),artistImageDefaultPath), 'imageFullPath'],
            ],  
          },    
          where: whereConstraint,
          order: [
                ['artistName', 'ASC'], 
          ],
            raw:true,
            nest: true,     
        })
        .then((data) => {
            resolve(data);
        });  
    }); 
  }

我的问题是
const 艺术家数据 = 艺术家服务.customfindAll(whereConstraint);
不等数据。 .所以我得到了结果，下面有提到。实际上是artistData属性列，需要结果数据。

{
    "status": 200,
    "message": "ok",
    "data": [
        {
            "id": 1,
            "fileType": "1",
            "customFileName": "test filename",
            "artists": "[{\"artistId\":1},{\"artistId\":4},{\"artistId\":2}]",
            "accompanyingArtists": "[{\"instrumentId\":1,\"accompanyingArtistId\":1},{\"instrumentId\":2,\"accompanyingArtistId\":6},{\"instrumentId\":3,\"accompanyingArtistId\":4}]",
            "Active": "true11",
            "artistData": {}
        },
        {
            "id": 2,
            "fileType": "1",
            "customFileName": "new file name",
            "artists": "[{\"artistId\":1},{\"artistId\":4},{\"artistId\":2},{\"artistId\":6},{\"artistId\":3}]",
            "accompanyingArtists": "[{\"instrumentId\":1,\"accompanyingArtistId\":1},{\"instrumentId\":2,\"accompanyingArtistId\":6},{\"instrumentId\":3,\"accompanyingArtistId\":4},{\"instrumentId\":3,\"accompanyingArtistId\":3},{\"instrumentId\":4,\"accompanyingArtistId\":2}]",
            "Active": "true11",
            "artistData": {}
        }
    ]
}

在控制台页面中，我的艺术家数据属性待定...
enter image description here

Answer 1

customFindAll 函数返回一个 Promise，但 forEach 不会等待它。添加一个 await :

const artistData = await artistService.customfindAll(whereConstraint);

此外， forEach 不会等待，它只是触发异步函数并继续前进。要等待 forEach 完成，您需要一个 map 和一个 Promise.all ，如下所示:

    await Promise.all(data.map(async (element) => {
        const artistsArray = [];
        let whereConstraint = {};
        JSON.parse(element.artists).forEach( async (ele) => { 
          artistsArray.push(ele.artistId);
        });;
        whereConstraint = {
          id : {
            [Op.in]: artistsArray
          }
        }
        element.Active = "true11";
        const artistData =  await artistService.customfindAll(whereConstraint);
        element.artistData = artistData;
        console.log("artistData",artistData); 
    }));

它以这种方式工作的方式是 data.forEach(async (e) => ... 运行异步函数并丢弃结果( promise )。如果您使用 map ，例如 data.map(async (e) => ... ，您将获得一个 Promise 数组，然后使用 await Promise.all(...) 等待它们。