Promise.all with Firebase DataSnapshot.forEach
13,802
You have to execute the Promise.all after you filled the array with promises, i.e. inside the then callback:
function loadMeetings(city,state) {
//$('#meetingsTable').empty();
return ref.child('states').child(state).child(city).once('value').then(function(snapshot) {
var reads = [];
// ^^^^^^^^^^^^^^
snapshot.forEach(function(childSnapshot) {
var id = childSnapshot.key;
var promise = ref.child('meetings').child(id).once('value').then(function(snap) {
// The Promise was fulfilled.
}, function(error) {
// The Promise was rejected.
console.error(error);
});
reads.push(promise);
});
return Promise.all(reads);
// ^^^^^^^^^^^^^^^^^
}, function(error) {
// The Promise was rejected.
console.error(error);
}).then(function(values) {
console.log(values); // [snap, snap, snap]
});
}
Author by
Ronnie Royston
Tulane University (Philosophy '97), Cisco Certified Internetworking Expert (CCIE# 6824), and USPA Master Skydiver (D# 20776).
Updated on June 10, 2022Comments
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Ronnie Royston about 2 years
I have a couple of HTML select's (dropdowns) that are populated from a Firebase node called "states" (see image below). Upon choosing a city, the below function fires and should retrieve all meetings occurring in that City. There is a separate "meetings" node and each meeting has various key/value pairs such as street, time, etc.
I (think that I) want to use Promise.all because I want to do a Firebase read (a .once on each meetingID) inside the DataSnapshot.forEach. Below does not work.
function loadMeetings(city,state){ //$('#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 </label><select class=\"form-control\" id=\"ddState\" disabled></select></div><div class=\"form-group\"><label for=\"ddState\"> </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 } } } }
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Ronnie Royston over 8 yearsI'm not getting anything in the final values. undefined.
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Bergi over 8 yearsThat means you're returning
undefined(or don'treturnanything) from thethencallback where you are creating the promises you're pushing intoreads. If you just want toreturn snap;there, omit the callback completely. -
Frank van Puffelen over 8 years@Bergi the
snapshotvariable is a DataSnapshot object from the Firebase JavaScript SDK. While it implementsforEach()it doesn't implementmap(). -
Frank van Puffelen over 8 yearsWorking jsbin of Bergi's code: jsbin.com/hotemaquho/edit?js,console. The only change is that you need to ensure you return something from the inner
then(). -
Haves almost 7 yearsYou also have to change childSnapshot.key(); to childSnapshot.key;
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Bergi almost 7 years@Haves no idea, I just took the OP's code from the question.
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Mustafa over 4 yearsI have tried all kinds of solutions for 2 days but I have not been successful. Finally I solved it thanks to your solution! Thanks @Bergi
