I'm making a note app and I have a problem. It is how to check if Firebase Firestore user data collection is empty.
Query query = firebaseFirestore.collection("mNotes").document(firebaseUser.getUid()).collection("userNotes").orderBy("title", Query.Direction.ASCENDING);
FirestoreRecyclerOptions<firebasemodel> allusernotes = new FirestoreRecyclerOptions.Builder<firebasemodel>().setQuery(query, firebasemodel.class).build(); ```
this code is used to get data from Firestore.
how can I check user data collection is empty with the if statement.
I am a beginner.
How to check Firebase Firestore user data collection is empty?
Firestore doesn't have the concept of an empty collection. If a collection doesn't contain any documents, it doesn't exist at all. So there is no API that can help you check if a collection actually exists. A collection in Firestore will start to exist if there is at least one document present in it.
So to solve this, you might consider checking the number of documents within the collection or subcollection like this:
val db = Firebase.firestore
val usersRef = db.collection("users")
usersRef.get().addOnCompleteListener {
if (it.isSuccessful) {
val numberOfDocs = it.result.documents.size
if (numberOfDocs > 0) {
Log.d(TAG,"users collection already exists!")
}
}
}
I have tried this code but it giving me blank list.
Future getDocs() async {
QuerySnapshot querySnapshot = await FirebaseFirestore.instance.collection("users").get();
for (int i = 0; i < querySnapshot.docs.length; i++) {
var a = querySnapshot.docs[i];
print(a.id);
}
}
If you check the bottom right of your screenshots, it says:
The document does not exist, it will not appear in queries or snapshots.
So while there is a document ID, that is only shown in the console so that you can select the subcollections. There is no actual document data for the selected document ID.
In fact, all the document IDs in your users collection are shown in italic, because there are no actual documents for any of them. And as the message says, that means they won't show up in read operations.
The simplest way to get the user documents too, is to actually create those documents when you also add the subcollection. What fields you add to the document doesn't really matter, but I tend to start with a createdAt timestamp.
Alternatively, you can run a collection group query across one of the subcollections and then for each resulting document look up the parent document, so determine the IDs.
Something like:
QuerySnapshot querySnapshot = await
FirebaseFirestore.instance.collectionGroup("user_info").get();
// 👆 collection group query
for (int i = 0; i < querySnapshot.docs.length; i++) {
var doc = querySnapshot.docs[i];
print(doc.id);
print(doc.reference.parent.parent.id); // 👈 print parent document id
}
Given that you may end up reading way more documents here, I'd consider this a workaround though, and typically only use it to generate the missing data once.
Also see:
Firestore DB - documents shown in italics
How to access all documents, my all documents only have sub collection in firestore
I am trying to show to user items, he participated in (for example liked posts). Now I store in user document (in users collection) IDs of documents from another collection (posts) and when I want to show them in recycler view firstly I get IDs from user document. Then I get all posts by IDs. Is there any workaround, where I would be able to store user ID in subcollection of post document and then get query of all liked/commented/whatever posts by user? So user document will not have reference to post's IDs and in posts collection I am able to do something like:
Query ref = from db.collection("posts") get all posts where post.likedBy == user;
I do no like idea of putting all users who liked the post into post document - user downloads all ids.
posts (collection)
-postID (post document)
-authorID, ... (fields)
users (collections)
-userID (user document)
-string[] idsOfPosts (fields)
You should use Subcollections as your data model.
Documents in subcollections can contain subcollections as well,
allowing you to further nest data. You can nest data up to 100 levels
deep.
Also you can use a collection group query to retrieve documents from a collection group instead of from a single collection. The link provides you with sample code snippets in different languages.
EDIT:
Based on the use case you have provided in the comments:
I would say the way you are describing your data model to get all posts liked by a user, it would need a query inside a query. Not sure if it's even feasible or efficient.
Here is my suggestion:
Build your data model similar to the following
This way running the following query (I'm using NodeJs) would give you all posts liked by user1.
let postsRef = db.collection('posts');
const user1 = postsRef.where('Liked', 'array-contains',
'user1');
let query1 = user1.get()
.then(snapshot => {
if (snapshot.empty) {
console.log('No matching documents.');
return;
}
snapshot.forEach(doc => {
console.log(doc.id, '=>', doc.data());
});
})
.catch(err => {
console.log('Error getting documents', err);
});
Output:
EDIT: (11/12/2019)
Based on what you have described in the comments, here is an idea that might solve your issue:
Instead of having a list of the Users who liked the post, you can have a reference to a Document that contains the list of users. You can reference to as many Documents as you wish.
Example:
The Documents can be even in a different Collection.
I have a collection called lists and it has documents who is ID represents the list ID. This document has a collection called employees and another one called locations.
The structure looks like this:
(lists)
-listId
(employees)
(locations)
If the user wants to delete a specific list then the problem is that we can't delete listId because that will keep the collection (as was mentioned by Firestore docs).
How can the structure be modeled to fit the needs? I can't seem to get around the need for subcollection.
Any recommendation?
There is no need to restructure your database in order to delete some collections. To delete an entire collection or subcollection in Cloud Firestore, retrieve all the documents within the collection or subcollection and delete them. So in order to delete a specific list, please use the following steps:
Find all documents beneath employees collection and delete them
Find all documents beneath locations collection and delete them
Delete the listId document
If you have larger collections, you may want to delete the documents in smaller batches to avoid out-of-memory errors. Repeat the process until you've deleted the entire collection or subcollection.
Even if the delete operation is not recomended by Firebase team because it has negative security and performance implications, you can still do it but only for small collections. If you need to delete entire collections for web, do so only from a trusted server environment.
For Android, you can use the following code:
private void deleteCollection(final CollectionReference collection, Executor executor) {
Tasks.call(executor, () -> {
int batchSize = 10;
Query query = collection.orderBy(FieldPath.documentId()).limit(batchSize);
List<DocumentSnapshot> deleted = deleteQueryBatch(query);
while (deleted.size() >= batchSize) {
DocumentSnapshot last = deleted.get(deleted.size() - 1);
query = collection.orderBy(FieldPath.documentId()).startAfter(last.getId()).limit(batchSize);
deleted = deleteQueryBatch(query);
}
return null;
});
}
#WorkerThread
private List<DocumentSnapshot> deleteQueryBatch(final Query query) throws Exception {
QuerySnapshot querySnapshot = Tasks.await(query.get());
WriteBatch batch = query.getFirestore().batch();
for (DocumentSnapshot snapshot : querySnapshot) {
batch.delete(snapshot.getReference());
}
Tasks.await(batch.commit());
return querySnapshot.getDocuments();
}
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.