Jesse Jesse - 1 month ago 13
Node.js Question

Node.js + Firebase orderByChild not working

I am trying to figure out this nested ordering and nothing I do will work.

Here is a sample of the data structure I am trying to order:

{
"-KV_Lrm_93Agm8kAuXql": {
"body": {
"Acceleration": "0.0",
"Altitude": "11",
"Battery": "12.7",
"Date": "2016/09/10",
"order": 1,
"time": "2016-10-19T20:26:32Z"
}
},
"-KV_LuTfJ9VrKRHoRWuw": {
"body": {
"Acceleration": "0.0",
"Altitude": "11",
"Battery": "12.7",
"Date": "2016/09/10",
"order": 5,
"time": "2016-10-21T20:26:32Z"
}
},
"-KV_Lx9VABuEB8D3I-i1": {
"body": {
"Acceleration": "0.0",
"Altitude": "11",
"Battery": "12.7",
"Date": "2016/09/10",
"order": 2,
"time": "2016-10-01T20:26:32Z"
}
},
"-KV_LzQOM3rHEKQuwyHQ": {
"body": {
"Acceleration": "0.0",
"Altitude": "11",
"Battery": "12.7",
"Date": "2016/09/10",
"order": 10,
"time": "2016-09-01T20:26:32Z"
}
},
"-KV_M0fdznAbKanHoY91": {
"body": {
"Acceleration": "0.0",
"Altitude": "11",
"Battery": "12.7",
"Date": "2016/09/10",
"order": 6,
"time": "2016-09-20T20:26:32Z"
}
}
}


Per the firebase documentation (https://firebase.googleblog.com/2015/09/introducing-multi-location-updates-and_86.html) you can do a "deep path query". In my case, if I want to sort by order I should be able to do:

.orderByChild("body/order")


But this does nothing. It has no effect on the ordering of the results. I have tried ordering on Date and time as well and neither work. Here is my full node function. This returns the results, just not ordered:

app.get('/api/xirgo-data', function(req, res)
{
var ref = db.ref("xirgo");
ref
.orderByChild("body/order")
.on("value", function(snap) {
return res.json(snap.val());
});
});


Thanks!

Answer

When you request the value of a query in Firebase, the resulting snapshot contains the keys, values and ordering information for the matching children.

But when you then convert this to a dictionary/associative array/JavaScript object, the ordering information is lost since JavaScript objects are inherently unordered.

To ensure you can access the matching items in the correct order, use the built-in DataSnapshot.forEach() method:

var ref = db.ref("xirgo");
ref
.orderByChild("body/order")
.on("value", function(snapshot) {
    snapshot.forEach(function(child) {
        console.log(child.key+': '+child.val());
    });
});
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