I thought I read that you can query subcollections with the new Firebase Firestore, but I don't see any examples. For example I have my Firestore setup in the following way:
Dances [collection]
danceName
Songs [collection]
songName
How would I be able to query "Find all dances where songName == 'X'"
Update 2019-05-07
Today we released collection group queries, and these allow you to query across subcollections.
So, for example in the web SDK:
db.collectionGroup('Songs')
.where('songName', '==', 'X')
.get()
This would match documents in any collection where the last part of the collection path is 'Songs'.
Your original question was about finding dances where songName == 'X', and this still isn't possible directly, however, for each Song that matched you can load its parent.
Original answer
This is a feature which does not yet exist. It's called a "collection group query" and would allow you query all songs regardless of which dance contained them. This is something we intend to support but don't have a concrete timeline on when it's coming.
The alternative structure at this point is to make songs a top-level collection and make which dance the song is a part of a property of the song.
UPDATE
Now Firestore supports array-contains
Having these documents
{danceName: 'Danca name 1', songName: ['Title1','Title2']}
{danceName: 'Danca name 2', songName: ['Title3']}
do it this way
collection("Dances")
.where("songName", "array-contains", "Title1")
.get()...
#Nelson.b.austin Since firestore does not have that yet, I suggest you to have a flat structure, meaning:
Dances = {
danceName: 'Dance name 1',
songName_Title1: true,
songName_Title2: true,
songName_Title3: false
}
Having it in that way, you can get it done:
var songTitle = 'Title1';
var dances = db.collection("Dances");
var query = dances.where("songName_"+songTitle, "==", true);
I hope this helps.
UPDATE 2019
Firestore have released Collection Group Queries. See Gil's answer above or the official Collection Group Query Documentation
Previous Answer
As stated by Gil Gilbert, it seems as if collection group queries is currently in the works. In the mean time it is probably better to use root level collections and just link between these collection using the document UID's.
For those who don't already know, Jeff Delaney has some incredible guides and resources for anyone working with Firebase (and Angular) on AngularFirebase.
Firestore NoSQL Relational Data Modeling - Here he breaks down the basics of NoSQL and Firestore DB structuring
Advanced Data Modeling With Firestore by Example - These are more advanced techniques to keep in the back of your mind. A great read for those wanting to take their Firestore skills to the next level
What if you store songs as an object instead of as a collection? Each dance as, with songs as a field: type Object (not a collection)
{
danceName: "My Dance",
songs: {
"aNameOfASong": true,
"aNameOfAnotherSong": true,
}
}
then you could query for all dances with aNameOfASong:
db.collection('Dances')
.where('songs.aNameOfASong', '==', true)
.get()
.then(function(querySnapshot) {
querySnapshot.forEach(function(doc) {
console.log(doc.id, " => ", doc.data());
});
})
.catch(function(error) {
console.log("Error getting documents: ", error);
});
NEW UPDATE July 8, 2019:
db.collectionGroup('Songs')
.where('songName', isEqualTo:'X')
.get()
I have found a solution.
Please check this.
var museums = Firestore.instance.collectionGroup('Songs').where('songName', isEqualTo: "X");
museums.getDocuments().then((querySnapshot) {
setState(() {
songCounts= querySnapshot.documents.length.toString();
});
});
And then you can see Data, Rules, Indexes, Usage tabs in your cloud firestore from console.firebase.google.com.
Finally, you should set indexes in the indexes tab.
Fill in collection ID and some field value here.
Then Select the collection group option.
Enjoy it. Thanks
You can always search like this:-
this.key$ = new BehaviorSubject(null);
return this.key$.switchMap(key =>
this.angFirestore
.collection("dances").doc("danceName").collections("songs", ref =>
ref
.where("songName", "==", X)
)
.snapshotChanges()
.map(actions => {
if (actions.toString()) {
return actions.map(a => {
const data = a.payload.doc.data() as Dance;
const id = a.payload.doc.id;
return { id, ...data };
});
} else {
return false;
}
})
);
Query limitations
Cloud Firestore does not support the following types of queries:
Queries with range filters on different fields.
Single queries across multiple collections or subcollections. Each query runs against a single collection of documents. For more
information about how your data structure affects your queries, see
Choose a Data Structure.
Logical OR queries. In this case, you should create a separate query for each OR condition and merge the query results in your app.
Queries with a != clause. In this case, you should split the query into a greater-than query and a less-than query. For example, although
the query clause where("age", "!=", "30") is not supported, you can
get the same result set by combining two queries, one with the clause
where("age", "<", "30") and one with the clause where("age", ">", 30).
I'm working with Observables here and the AngularFire wrapper but here's how I managed to do that.
It's kind of crazy, I'm still learning about observables and I possibly overdid it. But it was a nice exercise.
Some explanation (not an RxJS expert):
songId$ is an observable that will emit ids
dance$ is an observable that reads that id and then gets only the first value.
it then queries the collectionGroup of all songs to find all instances of it.
Based on the instances it traverses to the parent Dances and get their ids.
Now that we have all the Dance ids we need to query them to get their data. But I wanted it to perform well so instead of querying one by one I batch them in buckets of 10 (the maximum angular will take for an in query.
We end up with N buckets and need to do N queries on firestore to get their values.
once we do the queries on firestore we still need to actually parse the data from that.
and finally we can merge all the query results to get a single array with all the Dances in it.
type Song = {id: string, name: string};
type Dance = {id: string, name: string, songs: Song[]};
const songId$: Observable<Song> = new Observable();
const dance$ = songId$.pipe(
take(1), // Only take 1 song name
switchMap( v =>
// Query across collectionGroup to get all instances.
this.db.collectionGroup('songs', ref =>
ref.where('id', '==', v.id)).get()
),
switchMap( v => {
// map the Song to the parent Dance, return the Dance ids
const obs: string[] = [];
v.docs.forEach(docRef => {
// We invoke parent twice to go from doc->collection->doc
obs.push(docRef.ref.parent.parent.id);
});
// Because we return an array here this one emit becomes N
return obs;
}),
// Firebase IN support up to 10 values so we partition the data to query the Dances
bufferCount(10),
mergeMap( v => { // query every partition in parallel
return this.db.collection('dances', ref => {
return ref.where( firebase.firestore.FieldPath.documentId(), 'in', v);
}).get();
}),
switchMap( v => {
// Almost there now just need to extract the data from the QuerySnapshots
const obs: Dance[] = [];
v.docs.forEach(docRef => {
obs.push({
...docRef.data(),
id: docRef.id
} as Dance);
});
return of(obs);
}),
// And finally we reduce the docs fetched into a single array.
reduce((acc, value) => acc.concat(value), []),
);
const parentDances = await dance$.toPromise();
I copy pasted my code and changed the variable names to yours, not sure if there are any errors, but it worked fine for me. Let me know if you find any errors or can suggest a better way to test it with maybe some mock firestore.
var songs = []
db.collection('Dances')
.where('songs.aNameOfASong', '==', true)
.get()
.then(function(querySnapshot) {
var songLength = querySnapshot.size
var i=0;
querySnapshot.forEach(function(doc) {
songs.push(doc.data())
i ++;
if(songLength===i){
console.log(songs
}
console.log(doc.id, " => ", doc.data());
});
})
.catch(function(error) {
console.log("Error getting documents: ", error);
});
It could be better to use a flat data structure.
The docs specify the pros and cons of different data structures on this page.
Specifically about the limitations of structures with sub-collections:
You can't easily delete subcollections, or perform compound queries across subcollections.
Contrasted with the purported advantages of a flat data structure:
Root-level collections offer the most flexibility and scalability, along with powerful querying within each collection.
My situation is that I am creating a social media app, and I have an array of all of the people that the user is following. It looks like this:
let followingArray:[String] = ["user1Uid", "user2Uid", "user3Uid", "user4Uid"]
So, I want to perform a function using every userUid in the array to fetch their posts and display it onto a collectionView.
To give more context the function looks like this (the "userUid" is the element that I need to repeat with all of the userUid's using the array):
databaseRef.child("posts").child(userUid).observeSingleEvent(of: .value) { (snapshot) in
// all of the code to get the posts information into another array to display on the collection view.
}
Thanks a lot!
To do something with every element in an array you can always use forEach(_:). Try:
let followingArray:[String] = ["user1Uid", "user2Uid", "user3Uid", "user4Uid"]
for userID in followingArray {
databaseRef.child("posts").child(userID).observeSingleEvent(of: .value) { (snapshot) in
// all of the code to get the posts information into another array to display on the collection view.
}
}
I'm currently developing an App using Ionic 3 and Firebase. I'm using ionic-selectable (you can see my stackblitz here) for the user to select an option from my firebase database array and return the selected option to the user's id.
I have got everything to work, except that ionic-selectable is not reading the retrieved array form firebase.
I'm retrieving the array using the following code:
this.itemsRefdiag = afg.list('medicalhx');
this.items = this.itemsRefdiag.snapshotChanges().map(changes => {
return changes.map(c => ({ ...c.payload.val() }));
});
const dgRef = this.afg.database.ref();
dgRef.child('medicalhx').orderByChild('name').on('value', snapshot => { this.snapshot2 = JSON.stringify(snapshot).replace(/"[0-9]":{"name":|{|}/g, ""); })
My console.log results in:
"Hyperthyroidism","Hypothyroidism","Diabetes Type 1","Diabetes Type 2"
However, when using ionic-selectable for private diagnoses: Diagnosis[] = [this.snapshot2], I get 'undefined' options. However, when I manually type in private diagnoses: Diagnosis[] = ["Hyperthyroidism","Hypothyroidism","Diabetes Type 1","Diabetes Type 2"], it works. I also tried parsing the JSON array using the following code instead:
this.itemsRefdiag = afg.list('medicalhx');
this.items = this.itemsRefdiag.snapshotChanges().map(changes => {
return changes.map(c => ({ ...c.payload.val() }));
});
const dbRef = this.afg.database.ref();
dbRef.child('medicalhx').orderByChild('name').on('value', snapshot =>
{ let snapshot3 = JSON.stringify(snapshot).replace(/"}/g, `"`);
let snapshot4 = snapshot3.replace(/"[0-9]":{"name":|{|}|"/g, "");
this.snapshot2 = snapshot4.split(",");
});
My console.log results in an Object with separate strings (an array):
["Hyperthyroidism","Hypothyroidism","Diabetes Type 1","Diabetes Type 2"]
However, ionic-selectable still doesn't seem to read that and I get undefined error. Any ideas on what I may be doing wrong with the array?
EDIT
It actually does work the second time around, however the console error pops up the first time and I believe this is because it's not waiting for the array results to pop-up the first time around. Is there a way to add a wait time until the array loads?
The second code listed in the question converting it to a real array worked but required a loading time, hence poping up a console error. I managed to get around the loading time issue by implementing Asynchronous searching as per this stackblitz.
Suppose I have 2 Schema's in Mongoose that look like this:
var movieSchema = mongoose.Schema({
name: String,
type: String
});
var moviePlaylistSchema = mongoose.Schema({
name: String,
movies: [{type: mongoose.Schema.Types.ObjectId, ref: 'Movie'}]
});
var Movie = mongoose.model('Movie', movieSchema);
var MoviePlaylist = mongoose.model('MoviePlaylist', moviePlaylistSchema);
If a query was made along the following lines:
MoviePlaylist.find({}).populate('movies').exec(function(err, res) {
if (err) console.log('err', err);
else {
console.log('res', res);
res.forEach(function(elem, index) {
console.log('elem.name', elem.name);
});
}
});
Would the order of the elements in the array be maintained? The objective here is to allow the user to maintain a playlist order of their movies. If, when the "populate" method fires, the array order of Movie object Ids is not maintained, then this will not serve my purpose. Hence thought I'd ask someone who is more knowledgeable in this area.
If this works, then I have another task which is allowing the user to change the order of movies in the playlist, which should be straight forward by allowing the movie object id index to be swapped in the array.
Thanks for your help in advance.
MongoDB will keep the order of the array, much like an array in any programming language.
You can view the BSON/JSON spec for reference which highlights that the array must contain integer values for keys, and be maintained in ascending numerical order.
Additionally, the Mongoose populate on an array works by calling Model.populate via forEach on each element of the array. This modifies the array in place, hence the order is preserved. You can see the relevant source code here.
Using Parse.com and its Cloud code, I want to fetch users that are not in array of users.
...
var query = new Parse.Query(Parse.User);
query.notContainedIn("objectId", request.object.get("recipients"));
...
query.find().then(
function(results) {
console.log("# of users:" + results.length);
},
function(error) {
console.error(error)
}
);
The constraint notContainedIn doesn't seem to work, all users are returned, not just the ones not contained in the recipients array coming as part of the request object.
The recipients array in REST request is defined like this
"recipients":[
{"__type":"Pointer","className":"_User","objectId":"qwerty1234"},
{"__type":"Pointer","className":"_User","objectId":"asdfgh1234"}]
The data I get as part of the request is ok, because e.g. request.object.get("recipients")[0].id returns the qwerty1234 value.
What am I doing wrong here?
You are asking parse to compare the objectId to an array of pointers. This would work fine if the column was a Pointer to a User, but you're using just the ID.
The easy solution is to map or extract the ID from the array of pointers, e.g.
// at the top, so you can use the Underscore library
var _ = require('underscore');
// ...
// in your Cloud function
var query = new Parse.Query(Parse.User);
// _.pluck() creates an array of a property from each object in the parent array
var recipientObjectIds = _.pluck(request.object.get('recipients'), 'objectId');
query.notContainedIn('objectId', recipientObjectIds);