使用FirebaseDataSnapshot.forEach进行Promise.all-Promise.allwithFirebaseDataSnapshot.forEach

作者：goxtop | 来源：互联网 | 2023-05-19 16:21

IhaveacoupleofHTMLselects(dropdowns)thatarepopulatedfromaFirebasenodecalledstates

I have a couple of HTML select's (dropdowns) that are populated from a Firebase node called "states" (see image below). Upon choosing a city, the below function fires and should retrieve all meetings occurring in that City. There is a separate "meetings" node and each meeting has various key/value pairs such as street, time, etc.

我有几个HTML select（下拉列表），它们是从名为“states”的Firebase节点填充的（见下图）。选择城市后，以下功能将触发，并应检索该城市中发生的所有会议。有一个单独的“会议”节点，每个会议都有各种键/值对，如街道，时间等。

I (think that I) want to use Promise.all because I want to do a Firebase read (a .once on each meetingID) inside the DataSnapshot.forEach. Below does not work.

我（认为我）想要使用Promise.all，因为我想在DataSnapshot.forEach中执行Firebase读取（每个meetingID上的.once）。以下不起作用。

function loadMeetings(city,state){
    //$('#meetingsTable').empty();
    var reads = [];
    ref.child('states').child(state).child(city).once('value').then(function(snapshot) {
        snapshot.forEach(function(childSnapshot) {
            var id = childSnapshot.key();
            var dfd = ref.child('meetings').child(id).once('value').then(function(snap) {
                // The Promise was fulfilled.
            }, function(error) {
                // The Promise was rejected.
                console.error(error);
            });
            reads.push( dfd );
        });       
    }, function(error) {
        // The Promise was rejected.
        console.error(error);
    });

    Promise.all(reads).then(function(values) { 
      console.log(values); // [snap, snap, snap] 
    });
}

{
  "geofire" : {
    "25dbab9c-8e4e-45ce-a69b-8641b6579560" : {
      ".priority" : "9q5cc9ye4w",
      "g" : "9q5cc9ye4w",
      "l" : [ 34.0677809, -118.4016105 ]
    },
    "3d2c7948-16e5-466c-b0d8-0a9e24ed7529" : {
      ".priority" : "7zzzzzzzzz",
      "g" : "7zzzzzzzzz",
      "l" : [ 0, 0 ]
    },
    "3fc846d4-7e55-4134-a0f5-9393aaf02269" : {
      ".priority" : "dhyy1zhnu1",
      "g" : "dhyy1zhnu1",
      "l" : [ 27.8130538, -80.42524100000003 ]
    },
    "5952bd9f-8438-44b0-addb-a5b806dab5da" : {
      ".priority" : "9vw1zzv421",
      "g" : "9vw1zzv421",
      "l" : [ 31.288082, -92.46505450000001 ]
    },
    "7001c8a7-c4f0-44ba-a4fc-2dba32097cc6" : {
      ".priority" : "9vqe68qs06",
      "g" : "9vqe68qs06",
      "l" : [ 30.1046126, -91.99056969999998 ]
    },
    "ecb350d6-6664-4f95-9c1c-2fd1d2f11a40" : {
      ".priority" : "9vrk9tstc9",
      "g" : "9vrk9tstc9",
      "l" : [ 30.353474, -90.98251599999998 ]
    }
  },
  "markup" : {
    "addMeeting" : "New Meeting

  
  
  
 
  
  
  
    Open Meeting     Closed Meeting  
    Mens Only 
   Womens Only 
   Childcare  
    Meditation 
   Speaker 
   Step  
    Español 
   Big Book 
   Discussion  
    Tradition 
   Beginner  
  ",
    "admin" : "  Welcome 
 Meetings  Add Manage 
 Users  Add Manage 
   Welcome.
Running Scripts...
 
Running Scripts...
Running Scripts...
Running Scripts...
Running Scripts...",
    "adminWelcome" : "This is the admin welcome pane",
    "login" : "
Log In




",
    "manageMeeting" : "Filter  
    "
  },
  "meetings" : {
    "25dbab9c-8e4e-45ce-a69b-8641b6579560" : {
      "author" : "Ron Royston",
      "beginner" : true,
      "bigBook" : true,
      "childcare" : false,
      "city" : "los angeles",
      "day" : "sunday",
      "discussion" : false,
      "hour" : "4",
      "key" : "25dbab9c-8e4e-45ce-a69b-8641b6579560",
      "latitude" : 34.0677809,
      "layer" : "",
      "longitude" : -118.4016105,
      "meditation" : false,
      "meetingOpen" : false,
      "min" : ":00",
      "name" : "highrise",
      "onlyMen" : false,
      "onlyWomen" : true,
      "spanish" : true,
      "speaker" : false,
      "state" : "california",
      "step" : false,
      "street" : "111 rodeo",
      "timeframe" : "pm",
      "timestamp" : 1457470568863,
      "tradition" : true,
      "type" : "",
      "user" : "facebook:196986260658947",
      "zip" : "90210"
    },
    "3d2c7948-16e5-466c-b0d8-0a9e24ed7529" : {
      "author" : "Ron Royston",
      "beginner" : false,
      "bigBook" : false,
      "childcare" : false,
      "city" : "baton rouge",
      "day" : "sunday",
      "discussion" : false,
      "hour" : "1",
      "key" : "3d2c7948-16e5-466c-b0d8-0a9e24ed7529",
      "latitude" : 0,
      "layer" : "",
      "longitude" : 0,
      "meditation" : false,
      "meetingOpen" : false,
      "min" : ":00",
      "name" : "asdf",
      "onlyMen" : false,
      "onlyWomen" : false,
      "spanish" : false,
      "speaker" : false,
      "state" : "louisiana",
      "step" : false,
      "street" : "234 kjhkj",
      "timeframe" : "am",
      "timestamp" : 1457470215505,
      "tradition" : false,
      "type" : "",
      "user" : "facebook:196986260658947",
      "zip" : "70817"
    },
    "3fc846d4-7e55-4134-a0f5-9393aaf02269" : {
      "author" : "Ron Royston",
      "beginner" : false,
      "bigBook" : true,
      "childcare" : true,
      "city" : "miami",
      "day" : "sunday",
      "discussion" : true,
      "hour" : "1",
      "key" : "3fc846d4-7e55-4134-a0f5-9393aaf02269",
      "latitude" : 27.8130538,
      "layer" : "",
      "longitude" : -80.42524100000003,
      "meditation" : false,
      "meetingOpen" : false,
      "min" : ":00",
      "name" : "beach",
      "onlyMen" : false,
      "onlyWomen" : false,
      "spanish" : true,
      "speaker" : false,
      "state" : "florida",
      "step" : false,
      "street" : "120 a1a",
      "timeframe" : "am",
      "timestamp" : 1457470499310,
      "tradition" : false,
      "type" : "",
      "user" : "facebook:196986260658947",
      "zip" : "33101"
    },
    "5952bd9f-8438-44b0-addb-a5b806dab5da" : {
      "author" : "Ron Royston",
      "beginner" : true,
      "bigBook" : false,
      "childcare" : false,
      "city" : "alexandria",
      "day" : "sunday",
      "discussion" : false,
      "hour" : "1",
      "key" : "5952bd9f-8438-44b0-addb-a5b806dab5da",
      "latitude" : 31.288082,
      "layer" : "",
      "longitude" : -92.46505450000001,
      "meditation" : false,
      "meetingOpen" : false,
      "min" : ":00",
      "name" : "howdy",
      "onlyMen" : false,
      "onlyWomen" : false,
      "spanish" : false,
      "speaker" : false,
      "state" : "louisiana",
      "step" : false,
      "street" : "5676 city park",
      "timeframe" : "am",
      "timestamp" : 1457470284850,
      "tradition" : true,
      "type" : "",
      "user" : "facebook:196986260658947",
      "zip" : "71301"
    },
    "7001c8a7-c4f0-44ba-a4fc-2dba32097cc6" : {
      "author" : "Ron Royston",
      "beginner" : false,
      "bigBook" : false,
      "childcare" : false,
      "city" : "lafayette",
      "day" : "sunday",
      "discussion" : false,
      "hour" : "1",
      "key" : "7001c8a7-c4f0-44ba-a4fc-2dba32097cc6",
      "latitude" : 30.1046126,
      "layer" : "",
      "longitude" : -91.99056969999998,
      "meditation" : false,
      "meetingOpen" : false,
      "min" : ":00",
      "name" : "test3",
      "onlyMen" : false,
      "onlyWomen" : false,
      "spanish" : false,
      "speaker" : false,
      "state" : "louisiana",
      "step" : false,
      "street" : "234 kjhkj",
      "timeframe" : "am",
      "timestamp" : 1457470252872,
      "tradition" : false,
      "type" : "",
      "user" : "facebook:196986260658947",
      "zip" : "70500"
    },
    "ecb350d6-6664-4f95-9c1c-2fd1d2f11a40" : {
      "author" : "Ron Royston",
      "beginner" : false,
      "bigBook" : false,
      "childcare" : false,
      "city" : "baton rouge",
      "day" : "sunday",
      "discussion" : false,
      "hour" : "5",
      "key" : "ecb350d6-6664-4f95-9c1c-2fd1d2f11a40",
      "latitude" : 30.353474,
      "layer" : "",
      "longitude" : -90.98251599999998,
      "meditation" : true,
      "meetingOpen" : false,
      "min" : ":00",
      "name" : "test1",
      "onlyMen" : false,
      "onlyWomen" : false,
      "spanish" : false,
      "speaker" : true,
      "state" : "louisiana",
      "step" : false,
      "street" : "18432 lake iris",
      "timeframe" : "pm",
      "timestamp" : 1457470192281,
      "tradition" : false,
      "type" : "",
      "user" : "facebook:196986260658947",
      "zip" : "70817"
    }
  },
  "states" : {
    "california " : {
      "los angeles" : {
        "25dbab9c-8e4e-45ce-a69b-8641b6579560" : true
      }
    },
    "florida " : {
      "miami" : {
        "3fc846d4-7e55-4134-a0f5-9393aaf02269" : true
      }
    },
    "louisiana " : {
      "alexandria" : {
        "5952bd9f-8438-44b0-addb-a5b806dab5da" : true
      },
      "baton rouge" : {
        "3d2c7948-16e5-466c-b0d8-0a9e24ed7529" : true,
        "ecb350d6-6664-4f95-9c1c-2fd1d2f11a40" : true
      },
      "lafayette" : {
        "7001c8a7-c4f0-44ba-a4fc-2dba32097cc6" : true
      }
    }
  }
}

enter image description here

1 个解决方案

#1

You have to execute the Promise.all after you filled the array with promises, i.e. inside the then callback:

在用promises填充数组后，你必须执行Promise.all，即在then回调中：

function loadMeetings(city,state) {
    //$('#meetingsTable').empty();
    return ref.child('states').child(state).child(city).once('value').then(function(snapshot) {
        var reads = [];
//      ^^^^^^^^^^^^^^
        snapshot.forEach(function(childSnapshot) {
            var id = childSnapshot.key();
            var promise = ref.child('meetings').child(id).once('value').then(function(snap) {
                // The Promise was fulfilled.
            }, function(error) {
                // The Promise was rejected.
                console.error(error);
            });
            reads.push(promise);
        });
        return Promise.all(reads);
//      ^^^^^^^^^^^^^^^^^
    }, function(error) {
        // The Promise was rejected.
        console.error(error);
    }).then(function(values) { 
        console.log(values); // [snap, snap, snap] 
    });
}

Btw, if snapshot is an array you can simplify your code by using map instead of forEach.

顺便说一下，如果快照是一个数组，你可以使用map而不是forEach来简化你的代码。

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