Promise.all with Firebase DataSnapshot.forEach

2019-01-23 07:24发布

站内问答 / JavaScript
1255 1 4

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.

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.

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" : "<form class=\"outline\"><div class=\"row\"><h1 class=\"blue topTitle col-xs-10 col-xs-offset-1 col-md-4 col-md-offset-4\">New Meeting</h1></div><br><div class=\"form-group row\"><div class=\"col-xs-10 col-xs-offset-1 col-md-3 col-md-offset-2\"> <input type=\"text\" class=\"form-control\" id=\"meetingName\" placeholder=\"Meeting Name\"> </div><div class=\"col-xs-10 col-xs-offset-1 col-md-4 col-md-pull-1\"> <input type=\"text\" class=\"form-control\" id=\"meetingStreet\" placeholder=\"Street\" required> </div></div><div class=\"form-group row\"><div class=\"col-xs-10 col-xs-offset-1 col-md-3 col-md-offset-2\"> <input type=\"text\" class=\"form-control\" id=\"meetingCity\" placeholder=\"City\" required> </div><div class=\"col-xs-10 col-xs-offset-1 col-md-2 col-md-pull-1\"> <select class=\"form-control c-select\" id=\"meetingState\" required><option>Alabama </option><option>Alaska</option><option>Arizona</option><option>Arkansas</option><option>California</option><option>Colorado</option><option>Connecticut</option><option>Delaware</option><option>Florida</option><option>Georgia</option><option>Hawaii</option><option>Idaho</option><option>Illinois</option><option>Indiana</option><option>Iowa</option><option>Kansas</option><option>Kentucky</option><option>Louisiana</option><option>Maine</option><option>Maryland</option><option>Massachusetts</option><option>Michigan</option><option>Minnesota</option><option>Mississippi</option><option>Missouri</option><option>Montana</option><option>Nebraska</option><option>Nevada</option><option>New Hampshire</option><option>New Jersey</option><option>New Mexico</option><option>New York</option><option>North Carolina</option><option>North Dakota</option><option>Ohio</option><option>Oklahoma</option><option>Oregon</option><option>Pennsylvania</option><option>Rhode Island</option><option>South Carolina</option><option>South Dakota</option><option>Tennessee</option><option>Texas</option><option>Utah</option><option>Vermont</option><option>Virginia</option><option>Washington</option><option>West Virginia</option><option>Wisconsin</option><option>Wyoming</option></select></div><div class=\"col-xs-10 col-xs-offset-1 col-md-2 col-md-pull-2\"> <input type=\"text\" class=\"form-control\" id=\"meetingZip\" placeholder=\"ZIP\" required> </div></div><div class=\"form-group row\"><div class=\"col-xs-5 col-xs-offset-1 col-md-2 col-md-offset-2\"> <input type=\"text\" class=\"form-control\" id=\"latitude\" placeholder=\"latitude\" disabled> </div><div class=\"col-xs-5 col-md-2 pull-left\"> <input type=\"text\" class=\"form-control\" id=\"longitude\" placeholder=\"longitude\" disabled> </div></div><div class=\"form-group row\"><div class=\"col-xs-10 col-xs-offset-1 col-md-2 col-md-offset-2\"><select class=\"form-control c-select\" id=\"weekday\"><option>Sunday</option><option>Monday</option><option>Tuesday</option><option>Wednesday</option><option>Thursday</option><option>Friday</option><option>Saturday</option></select></div><div class=\"col-xs-10 col-xs-offset-1 col-md-3 col-md-pull-1\"><div class=\"form-inline\"><div class=\"form-group\"><select class=\"form-control c-select\" id=\"hour\"><option>1</option><option>2</option><option>3</option><option>4</option><option>5</option><option>6</option><option>7</option><option>8</option><option>9</option><option>10</option><option>11</option><option>12</option></select><select class=\"form-control c-select\" id=\"minute\"><option>:00</option><option>:15</option><option>:30</option><option>:45</option></select><select class=\"form-control c-select\" id=\"timeframe\"><option>AM</option><option>PM</option></select></div></div></div></div><div class=\"form-group row\"><div class=\"col-xs-10 col-xs-offset-1 col-md-4 col-md-offset-2\"> <label class=\"radio-inline c-input c-radio\"> <input type=\"radio\" name=\"meetingType\" id=\"openMeeting\"> <span class=\"c-indicator\"></span> Open Meeting </label> <label class=\"radio-inline c-input c-radio\"> <input type=\"radio\" name=\"meetingType\" id=\"closedMeeting\" checked> <span class=\"c-indicator\"></span> Closed Meeting </label> </div></div><div class=\"form-group row\"><div class=\"col-xs-5 col-xs-offset-1 col-md-2 col-md-offset-2\"> <label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"mensOnly\"> <span class=\"c-indicator\"></span> Mens Only </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"womensOnly\"> <span class=\"c-indicator\"></span> Womens Only </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"childcare\"> <span class=\"c-indicator\"></span> Childcare </label> </div><div class=\"col-xs-5 col-xs-offset-1 col-md-2 col-md-pull-1\"> <label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"meditation\"> <span class=\"c-indicator\"></span> Meditation </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"speaker\"> <span class=\"c-indicator\"></span> Speaker </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"step\"> <span class=\"c-indicator\"></span> Step </label> </div></div><div class=\"form-group row\"><div class=\"col-xs-5 col-xs-offset-1 col-md-2 col-md-offset-2\"> <label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"spanish\"> <span class=\"c-indicator\"></span> Español </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"bigBook\"> <span class=\"c-indicator\"></span> Big Book </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"discussion\"> <span class=\"c-indicator\"></span> Discussion </label> </div><div class=\"col-xs-5 col-xs-offset-1 col-md-2 col-md-pull-1\"> <label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"tradition\"> <span class=\"c-indicator\"></span> Tradition </label><br><label class=\"c-input c-checkbox\"> <input type=\"checkbox\" id=\"beginner\"> <span class=\"c-indicator\"></span> Beginner </label> </div></div><div class=\"form-group row\"><div class=\"col-xs-5 col-xs-offset-8 col-md-2 col-md-offset-8\"> <input class=\"btn btn-primary\" type=\"submit\" id=\"submit\"></input> </div></div></form>",
    "admin" : "<ul id=\"tabs\" class=\"nav nav-tabs\"> <li class=\"nav-item\"> <a data-toggle=\"tab\" class=\"nav-link active\" href=\"#adminWelcome\" role=\"tab\">Welcome</a> </li><li class=\"nav-item dropdown\"> <a class=\"nav-link dropdown-toggle\" data-toggle=\"dropdown\" href=\"#\" role=\"button\" aria-haspopup=\"true\" aria-expanded=\"false\">Meetings</a> <div class=\"dropdown-menu\"> <a data-toggle=\"tab\" class=\"dropdown-item\" href=\"#addMeeting\">Add</a> <a data-toggle=\"tab\" class=\"dropdown-item\" href=\"#manageMeeting\">Manage</a> </div></li><li class=\"nav-item dropdown\"> <a class=\"nav-link dropdown-toggle\" data-toggle=\"dropdown\" href=\"#\" role=\"button\" aria-haspopup=\"true\" aria-expanded=\"false\">Users</a> <div class=\"dropdown-menu\"> <a data-toggle=\"tab\" class=\"dropdown-item\" href=\"#addUser\">Add</a> <a data-toggle=\"tab\" class=\"dropdown-item\" href=\"#manageUser\">Manage</a> </div></li></ul> <div class=\"tab-content\"> <div id=\"adminWelcome\" class=\"tab-pane fade in active\" role=\"tabpanel\"> <h3 class=\"topTitle\">Welcome.</h3><div class=\"loader\"><img src=\"images/loading.gif\"><p class=\"blue\">Running Scripts...</p></div><script>adminInit();</script> </div><div id=\"addMeeting\" class=\"tab-pane fade\" role=\"tabpanel\"><div class=\"loader\"><img src=\"images/loading.gif\"><p class=\"blue\">Running Scripts...</p></div></div><div id=\"manageMeeting\" class=\"tab-pane fade\" role=\"tabpanel\"><div class=\"loader\"><img src=\"images/loading.gif\"><p class=\"blue\">Running Scripts...</p></div></div><div id=\"addUser\" class=\"tab-pane fade\" role=\"tabpanel\"><div class=\"loader\"><img src=\"images/loading.gif\"><p class=\"blue\">Running Scripts...</p></div></div><div id=\"manageUser\" class=\"tab-pane fade\" role=\"tabpanel\"><div class=\"loader\"><img src=\"images/loading.gif\"><p class=\"blue\">Running Scripts...</p></div></div></div>",
    "adminWelcome" : "<p>This is the admin welcome pane</p>",
    "login" : "<div class=\"row topMargin myLogin col-xs-10 col-xs-offset-1 col-md-6 col-md-offset-3\"><br><h1 class=\"\">Log In</h1><br><div class=\"btn-group-vertical\" role=\"group\"><button class=\"btn btn-secondary myButton\" id=\"facebook\"><img src=\"images/facebook.png\" class=\"middle\" alt=\"Facebook logo\" height=\"24\"> Facebook</button><button class=\"btn btn-secondary myButton\" id=\"google\"><img src=\"images/google.png\" class=\"middle\" alt=\"Google logo\" height=\"24\"> Google</button><button class=\"btn btn-secondary myButton\" id=\"twitter\"><img src=\"images/twitter.png\" class=\"middle\" alt=\"Twitter logo\" height=\"24\"> Twitter</button></div><br><br><br></div>",
    "manageMeeting" : "<form class=\"form-inline outline\"><div class=\"form-group\"><label for=\"ddState\">Filter&nbsp; </label><select class=\"form-control\" id=\"ddState\" disabled></select></div><div class=\"form-group\"><label for=\"ddState\">&nbsp;&nbsp;&nbsp; </label><select class=\"form-control state\" id=\"ddCity\" disabled></select></div></form>"
  },
  "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条回答
我欲成王，谁敢阻挡
2楼-- · 2019-01-23 08:00

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

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.

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