循环访问数据以提取firebase值的数组

Question

我有一个由N条路径组成的数组，用于从firebase数据库中的不同位置检索数据。

searchpaths=[“locations/date1/imageid”,“locations/date2/imageid2”,locations/date3/imageid3,...]

    const searchPaths = ['locations/date1/imageID', 'locations/date2/imageID2']
    const imageURLs = []

     for(var Obj in searchPaths) 
    {
        const path = Obj
        admin.database().ref(path).once('value').then(snapshot => 
        { 
        const URL = snapshot.val().fileURL;
        imageURLs.push(URL);
        console.log('ImageURL: ' + URL );
        })
    // here is where it gets sour
    }.then(() => {
        console.log("All image URL's" + imageURLs")
    }

Answer 1

您可以使用for-loop创建一个许诺数组，然后使用promise.all，我知道它很粗糙，但应该可以工作。

const searchPaths = ['locations/date1/imageID', 'locations/date2/imageID2']
const imageURLs = []
var promises = [];
 for(var Obj in searchPaths) 
{
    promises.push(new Promise(function(resolve, reject) {
      const path = Obj
      admin.database().ref(path).once('value').then(snapshot => 
      { 
      const URL = snapshot.val().fileURL;
      imageURLs.push(URL);
      console.log('ImageURL: ' + URL );

      //resolve the promise after pushing imageURL
      resolve();
      })
    }));
}

//when all of them are done:
Promise.all(promises)
.then(function(results) {
  //code when done...
})