Node.js中按顺序从Firebase Storage获取文件URL并存入MongoDB

业务场景 #

Firebase Storage中有一个主文件夹，其下包含多个子文件夹，每个子文件夹内有两个文件。需要在Node.js中遍历每个子文件夹，获取其中每个文件的下载URL，并将每个子文件夹的两个URL作为一个文档存储到MongoDB中。

原实现代码 #

const info={}
const Ref = ref(storage, 'main folder in firebase')
listAll(Ref).then((res) => {
  res.prefixes.forEach((folderRef) => {
    console.log("prefix" + folderRef);
    listAll(folderRef).then((res) => {
      getDownloadURL(res.items[0])
        .then((url) => {
          console.log(url);
          if (url.search("html") === -1) {
            info.image = `${url}`;
          } else {
            info.doc = `${url}`;
          }
          return info;
        })
        .then((info) => {
          getDownloadURL(res.items[1])
            .then((url) => {
              console.log(url);
              if (url.search("html") === -1) {
                info.image = `${url}`;
              } else {
                info.doc = `${url}`;
              }
              return info;
            })
            .then((info) => {
              console.log(info);
            });
        });
    });
  });
});

Firebase Storage结构 #

main folder --> template1 (CV1.png, test.html) --> template2 (CV2.png, test.html) --> template3 (CV3.png, test.html)

错误输出 #

执行后生成的对象并未包含同一子文件夹的两个文件URL，输出示例：

prefixgs://my-first-project.appspot.com/data/template1
prefixgs://my-first-project.appspot.com/data/template2
prefixgs://my-first-project.appspot.com/data/template3
https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate1%2Fcv1.PNG
https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate2%2Fcv2.PNG?
https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate3%2Fcv3.PNG?
https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate1%2Ftest.html?

{
image: 'https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate3%2Fcv3.PNG?',
doc: 'https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate1%2Ftest.html?'
}
https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate2%2Ftest.html?

{
image: 'https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate3%2Fcv3.PNG?',
doc: 'https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate2%2Ftest.html?'
}
https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate3%2Ftest.html?

{
image: 'https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate3%2Fcv3.PNG?',
doc: 'https://firebasestorage.googleapis.com/v0/b/my-first-project-9f749.appspot.com/o/data%2Ftemplate3%2Ftest.html?'
}

解决方案 #

问题根源在于listAll()和getDownloadURL()都是异步函数，原代码未正确等待异步操作完成，导致不同子文件夹的URL互相覆盖。通过Promise.all()批量等待异步操作完成，确保每个子文件夹的两个URL被正确关联后再存入MongoDB。

修正后的代码：

listAll('main folder Reference').then((res) => {
  const folders = res.prefixes.map(folderRef => listAll(folderRef));
  Promise.all(folders).then((folderResults) => {
    folderResults.forEach((folderData) => {
      const fileUrlPromises = folderData.items.map(itemRef => getDownloadURL(itemRef));
      Promise.all(fileUrlPromises).then((urls) => {
        const info = {};
        urls.forEach((url) => {
          if (url.search("html") === -1) {
            info.image = url;
          } else {
            info.doc = url;
          }
        });
        console.log(info);
        const newList = new templates({
          ...info,
        });
        try {
          newList.save();
          console.log(info);
        } catch (error) {
          console.log(error);
        }
      });
    });
  });
});

内容的提问来源于stack exchange，提问作者Hasnain Ali