Develop Reference

Firestore - Query, then update

I want to return an item with a specific ID and perform an update operation on it. My query gets the right result, but it won't let me update it.
I tried following this tutorial: https://www.youtube.com/watch?v=mYyPbfpoZeM
And read the documentation. Both didn't help. Other threads to the same topic are, well, different.
I have a database of objects which have a unique ID stored as integer.
I have an HTML form to get an ID as user input and the query below to retrieve the according object.
I tried this. The query worked, the update didn't.
db.collection('objects').where('ID','==', ID ).get().then((snapshot) => {
snapshot.docs.forEach( doc => {
console.log('debug');
console.log(doc.data().ID);
})
});
I am still new to firebase and js, so please forgive me if my code is uterly wrong.
I am currently stuck with this:
db.collection('objects').where('ID','==', ID ).get().then((doc) => {
console.table(doc);
});
Which is still not working.
For the second snippet an I currently get an unlegible table in which I can't really find the object I was looking for.
How do I update a single value in a single document?
EDIT: I forgot my implementation attempts of the update function.
I tried doc.update({value:0}) inside the for loop in snippet one which yielded doc.update is not a function. Similarly for doc.data().update(...).
In the second snippet I mainly tried to see what I got returned and ran variations of the above mentioned uodate function. With no success.

I managed to get it to work by studying the part of the firestore documentation that goes more into detail about the actual functions. Somehow it was hard for me to find this.
db.collection("users").where("name", "==", somename).limit(1).get().then(query => {
console.log(query);
const thing = query.docs[0];
console.log(thing.data());
let tmp = thing.data();
tmp.current_game_play = tmp.current_game_play + 1;
console.log(tmp);
thing.ref.update(tmp);
});
So I use where to get a Query object, use get to get a a querySnapshot inside the then promise resolve, use docs[0] to retrieve the first (and only) documentSnapshot and finally ref to get a reference that makes the whole thing updatable later.

try this:
var objectRef= db.collection("objects").doc(ID);
objectRef.update({
value: 0
}).then(function() {
console.log("Document successfully updated!");
}).catch(function(error) {
// The document probably doesn't exist.
console.error("Error updating document: ", error);
});

Trying to get a snapshot of a variable from firebase gives me an error

Problem
In a social media app I am making with react native and firebase, I am trying to grab the number of comments a post has using the snapshot function of a variable I have saved on my servers, then I am going to add one to this variable when a user adds a new comment. My code to do so is right here:
firebase.database().ref('posts').child(this.state.passKey).update({
comments: firebase.database().ref('posts/'+this.state.passKey).child('comments').snapshot.val() + 1
})
When I actually run this code, I get an error saying:
Reference.child failed: First argument was an invalid path = "undefined".
Paths must be non-empty strings and can't contain ".","#","$","[", or "["
At first I thought this might be that the "this.state.passKey" wasn't actually passing the key, but putting in a key I copied from the server didn't fix the problem.
My Server
-

To get the comments of particular post you should do like this
let postId='someId'
postRef=`/posts/${postId}`
firebase.database().ref(postRef).once("value", dataSnapshot => {
comment=dataSnapshot.val().comments
});

It looks like you're expecting this bit of code to query the database:
firebase.database().ref('posts/'+this.state.passKey).child('comments').snapshot.val() + 1
Unfortunately, it doesn't work that way. There's no snapshot property on a database Reference object returned by child() or ref().
Instead, you'll need to query the database at that reference, then when you're called back with its value, you can apply it elsewhere.
var ref = firebase.database().ref('posts/'+this.state.passKey+'/comments')
ref.once('value', function(snapshot) {
// use the snapshot here
})

firebase admin with node.js: update in nested JSON tree

I use the below code on my Node.js admin server to retrieve data from my JSON tree, which works fine and prints the content of all snapshot2's to the console.
ref.once("value", function(snapshot0) {
snapshot0.forEach( function(snapshot1) {
snapshot1.child("Food").forEach( function(snapshot2) {
console.log(snapshot2.val());
});
});
});
However, how can I edit the data held at snapshot2?
If I try to call e.g.
snapshot2.update({250:42})
then it gives me the following error:
TypeError: snapshot2.update is not a function
I am really confused and think this must be a problem many people have?

You cannot update a snapshot. but you can update a reference, and you can get reference from snapshot by doing
snapshot.ref
, then you can do this to update
snapshot.ref.update({250:42})

Cloud code not working

i am new at parse..trying code..trying to run a trigger required in my project.but not able to track not even i am getting any error.
i am using cloud code i.e triggers...
what i want to do is, after update or save i want to run a trigger which will a column in a class with value of 200.
Parse.initialize('APPLICATION_ID', 'JAVASCRIPT_KEY');
Parse.Cloud.afterSave("match_status", function(request)
{
var query = new Parse.Query('Wallet');
query.set("wallet_coines_number", 200);
query.equalTo("objectId", "FrbLo6v5ux");
query.save();
});
i am using afterSave trigger in which match_status is my trigger name. after that i making a object called query of Wallet class. This object will set column 'wallet_coines_number' with the value 200 where objectId is FrbLo6v5ux. after that i used save function which will execute query.
Please guide me if i am wrong, or following wrong approach.
Thank You !

Have you read the Parse documentation on Cloud Code ?
The first line of your code is only relevant when you are initialising Parse JavaScript SDK in a web page, you do not need to initialise anything in Parse cloud code in the main.js file. Also you cannot use a query to save/update an object. A query is for searching/finding objects, when you want to save or update an object you need to create a Parse.Object and save that.
So you code should become something like:
Parse.Cloud.afterSave("match_status", function(request) {
var wallet = new Parse.Object('Wallet');
wallet.set("wallet_coines_number", 200);
wallet.set("objectId", "FrbLo6v5ux");
wallet.save();
});

jQuery Deferred returns only last value in loop

So I'm trying to go through one Firebase database to find entries in the database matching a criteria. Therefore I'm using the deferred object of jQuery to handle the database calls.
Once I get a return value from this first database I want to get the user info from a second database for each of those values in the first db. Then the results are added to a JSON array
so its:
<search for value, find one>
<<<search other db for oher info>>>
<continue search for outer value>
But this only returns one value - although everything else is running fine (and the console logs all the info correct).
Here's the code:
function find(searchLocation, profileID) {
var requestUserData = {
data: []
};
var def = $.Deferred();
//This will be executed as long as there are elements in the database that match the criteria and that haven't been loaded yet (so it's a simple loop)
Ref.orderByChild("location").equalTo(searchLocation).on("child_added", function(snapshot) {
def.ressolve(snapshot.val().ID);
});
return def.promise();
};
I hope you guys have any ideas on what to do or how I could solve this. Thanks in advance!
Edit: upon further testing I discovered that this problem already exists in the outer loop - so only the first value is being returned. I think this is related to the posission of the resolve() method but I didn't find a posibility on how to change this behaviour.

Firebase is a real-time database. The events stream as changes occur at the server. You're attempting to take this real-time model and force it into CRUD strategy and do a GET operation on the data. A better solution would be to simply update the values in real-time as they are modified.
See AngularFire, ReactFire, or BackboneFire for an example of how you can do this with your favorite bindings framework.
To directly answer the question, if you want to retrieve a static snapshot of the data, you want to use once() callback with a value event, not a real-time stream from child_added:
Ref.orderByChild("location").equalTo(searchLocation).once("value", function(snapshot) {
def.resolve(snapshot.val());
});