In my app, I have comments that have a field value of threadCommentCount. I want to order the comments using orderBy threadCommentCount descending and then have pagination continue this using startAfter(lastThreadCommentCount). The problem is when threadCommentCount is 0, which is a lot of them, it will return and the same data every time since it starts at 0 everytime. Here is the query:
popularCommentsQuery = db
.collection('comments')
.where('postId', '==', postId)
.orderBy('threadCommentCount', 'desc')
.startAfter(startAfter)
.limit(15)
.get()
This will return the same comments everytime once threadComment count is 0. I'm unable to send the last document snapshot because im using cloud functions and I dont want to send the documentSnapshot in a get query parameter. I don;t really care how the comments are ordered after threadCommentCount is 0, I just need to not get any duplicates. Any help is great!
All Firestore queries have an implicit orderBy("__name__", direction) to resolve any ties between documents that have the same values for the other named orderBy fields. This makes the final sort order stable. But it also enables you to pass another argument to startAfter to provide the document ID of the anchor document that you wish to use for the purpose of pagination.
.startAfter(lastThreadCommentCount, lastDocumentId)
Between these two values, you should be able to uniquely identify the document in the result set to start the next page.
so, I was trying OrderBy and StartAfter with two different fields(time,key) in firestore to establish pagination in flastList.
Key point is that we can pass document snapshot to define the query cursor [reference]
Here is how I managed to do it.
step 1: get the document Id(which is auto generated by firebase) with where() [reference]
const docRef = firestore().collection('shots').where('key','==','custom_key')
const fbDocIdGeneratedByFirebase= await docRef.get().docs[0].id;
step 2: get document snapshot with firebase generated document Id (which we got in the 1st step)
const docRef2= firestore().collection('shots').doc(fbDocIdGeneratedByFirebase)
const snapshot = await docRef2.get();
step 3: pass the snapshot got in step 2 to startAfter() so that the cursor will point there [reference]
let additionalQuery = firestore().collection('shots')
.orderBy("time", "desc")
.startAfter(snapshot)
.limit(this.state.limit)
let documentSnapshots = await additionalQuery.get(); // you know what to do next
...
Can you Improve the solution??
Related
I am trying to delete an entire object stored in Redis using LREM, but I don't think I am doing it right, below is the code I tried:
GraphQL mutation:
deleteImage: async(_,args) => {
let data = await client.lrem("postedImagesList",0,JSON.stringify(args.id));
return data
}
postedImagesList is a redis collection of all the object elements stringified:
1) "{\"id\":\"aadc8456-a5c9-46b9-a58c-670446d95c70\",\"url\":\"chas\",\"description\":\"asd\",\"posterName\":\"asda\",\"binned\":false,\"userPosted\":true}"
2) "{\"id\":\"a24d6d1b-224f-400d-8b84-dac83d8eaf92\",\"url\":\"ihir\",\"description\":\"helped\",\"posterName\":\"bhi\",\"binned\":false,\"userPosted\":true}"
I am given the id as an argument and I have to delete the entire object, how can I do so? I am adding the elements using lpushasync.
Please see the LREM docs.
LREM key count element
The element argument has to have an exact match, so you can't match by ID.
You might want to consider using the RedisJSON using the JSON.DEL you should be easily achieve what you're looking for.
I use firebase admin and realtime database on node.js
Data look like
When I want to get data where batch = batch-7, I was doing
let batch = "batch-7";
let ref = admin.database().ref('qr/');
ref.orderByChild("batch").equalTo(batch).on('value', (snapshot) =>
{
res.json(Object.assign({}, snapshot.val()));
ref.off();
});
All was OK!
But now i should create pagination, i.e. I should receive data on 10 elements depending on the page.
I use this code:
let page = req.query.page;// num page
let batch = req.params.batch;// batch name
let ref = admin.database().ref('qr/');
ref.orderByChild("batch").startAt(+page*10).limitToFirst(10).equalTo(batch)
.on('value', (snapshot) =>
{
res.json(Object.assign({}, snapshot.val()));
ref.off();
});
But I have error:
Query.equalTo: Starting point was already set (by another call to startAt or equalTo)
How do I get data in the amount of N, starting at position M, where batch equal my batch
You can only call one startAt (and/or endAt) OR equalTo. Calling both is not possible, nor does it make a lot of sense.
You seem to have a general misunderstanding of how startAt works though, as you're passing in an offset. Firebase queries are not offset based, but work purely on the value, often also referred to as an anchor node.
So when you want to get the data for a second page, and you order by batch, you need to pass in the value of batch for the anchor node; first item that you want to be returned. This anchor node is typically the last item of the previous page, since you don't know the first item of the next page yet. And for this anchor node, you need to know the value of the item you order on (batch) and usually also its key (if/when there may be multiple nodes with the same value for batch).
It also means that you usually request one item more than you need, which is the anchor node.
So when you request the first page, you should track the key/batch of the last node:
var lastKey, lastValue;
ref.orderByChild("batch").equalTo(batch).limitToFirst(10).on('value', (snapshot) => {
snapshot.forEach((child) => {
lastKey = child.key;
lastValue = child.child('batch').value();
})
})
Then when you need the second page, you do a query like that:
ref.orderByChild("batch").start(lastValue, lastKey).endAt(lastValue+"\uf8ff").limitToFirst(11).on('value', (snapshot) => {
snapshot.forEach((child) => {
lastKey = child.key;
lastValue = child.child('batch').value();
})
})
There's one more trick above here: I use startAt instead of equalTo, so that we can get pagination working. But it then uses endAt to ensure we still end at the correct item, by using the last known Unicode character as the last batch value to return.
I'd also highly recommend checking out some of the previous questions on pagination with the Firebase Realtime Database.
How do I limit .once('value') in firebase-admin?
Code:
async function GetStuff(limit, page){
const data = await ref.limitToFirst(parseInt(limit)).once('value')
return data.val();
}
I wanted to create a page system, where a it sends request for a limited amount of data, and the user can change the page to get different data, but for some reason, I can't get it to work.
The code above only gets the first 20(when limit is 20), but how can I make it start at 20, so I can make this page feature.
I thought:
Code:
async function GetStuff(limit, page){
const data = await ref.startAt(limit*page).limitToFirst(parseInt(limit)).once('value')
return data.val();
}
You might want to review the relevant documentation. It looks like you're trying to pass the offset of a child to startAt, but that's not how startAt works. It accepts the actual value of the child to start at. Pagination by offset index is not supported.
The way you use startAt is typically passing the last sorted value retrieved by the prior query (or, if you don't want to retrieve that value again, 1 + that value, or a string that is lexically greater than the last string received. As such, some data sets might actually be difficult to paginate if they have the same sorted value repeated many times.
Is there a way to get the index of the results within an aql query?
Something like
FOR user IN Users sort user.age DESC RETURN {id:user._id, order:{index?}}
If you want to enumerate the result set and store these numbers in an attribute order, then this is possible with the following AQL query:
LET sorted_ids = (
FOR user IN Users
SORT user.age DESC
RETURN user._key
)
FOR i IN 0..LENGTH(sorted_ids)-1
UPDATE sorted_ids[i] WITH { order: i+1 } IN Users
RETURN NEW
A subquery is used to sort users by age and return an array of document keys. Then a loop over a numeric range from the first to the last index of the that array is used to iterate over its elements, which gives you the desired order value (minus 1) as variable i. The current array element is a document key, which is used to update the user document with an order attribute.
Above query can be useful for a one-off computation of an order attribute. If your data changes a lot, then it will quickly become stale however, and you may want to move this to the client-side.
For a related discussion see AQL: Counter / enumerator
If I understand your question correctly - and feel free to correct me, this is what you're looking for:
FOR user IN Users
SORT user.age DESC
RETURN {
id: user._id,
order: user._key
}
The _key is the primary key in ArangoDB.
If however, you're looking for example data entered (in chronological order) then you will have to have to set the key on your inserts and/or create a date / time object and filter using that.
Edit:
Upon doing some research, I believe this link might be of use to you for AI the keys: https://www.arangodb.com/2013/03/auto-increment-values-in-arangodb/
What is wrong with this query?
const db = firebase.firestore()
const query = db.doc(this.props.user.uid).collection('statements').orderBy('uploadedOn', 'desc').limit(50)
I get the following error:
Uncaught Error: Invalid document reference. Document references must have an even number of segments, but FrMd6Wqch8XJm32HihF14tl6Wui2 has 1
at new FirestoreError (index.cjs.js:346)
at Function.DocumentReference.forPath (index.cjs.js:15563)
at Firestore.doc (index.cjs.js:15368)
at UploadStatementPresentation.componentWillMount (UploadStatementPage.jsx:61)
at UploadStatementPresentation.componentWillMount (createPrototypeProxy.js:44)
at callComponentWillMount (react-dom.development.js:6872)
at mountClassInstance (react-dom.development.js:6968)
at updateClassComponent (react-dom.development.js:8337)
at beginWork (react-dom.development.js:8982)
at performUnitOfWork (react-dom.development.js:11814)
Since you haven't described what exactly you're trying to query, I'll just point out that all documents must be in a collection, without exception. So, if you say this:
db.doc(this.props.user.uid)
Firestore assumes that the string you're passing to doc() contains both the collection and document id separated by a slash. But this seems to be highly unlikely in your case. You need to determine which collection the uid is in, and use that first when you build the reference to the collection you want to query. Assuming that you do have a statements subcollection in the uid document, and that some other collection contains the uid document, you'll have to specify the full path like this:
db.collection('that-other-collection').doc(this.props.user.uid).collection('statements')
Of course, only you know the actual structure of your data.
If you want to get a collection of documents with querying, you don’t have to specify a document id. Below code should work in this case.
const query = db.collection('statements').orderBy('uploadedOn', 'desc').limit(50)
Or if you want to get the document, you can pass the document id to doc() method. In that case, the code should be.
const query = db.collection('statements').doc(this.props.user.uid)
For more details about querying firestorm data: https://firebase.google.com/docs/firestore/query-data/get-data?authuser=0
For others having this issue, make sure that no document reference has an empty string.
I had this issue when using a get method with uid input as below and forgot to check if uid is empty
private fun getFullRef(uid: String): CollectionReference {
return ref.document(uid).collection(FireContact.SUB_PATH)
}