I'm using Firebase & Flutter and wondering how many reads does using .contains() produce?
For example: Let's say we have a button that you can click on and whenever the current user clicks on it, it takes their UID and stores it in an array/list in the Firestore Database.
Then I want to check if the current user's UID is inside of that list. To do this, I'm using .contains(uid). So as an example, let's say the list contains a total of 10 different values/UIDs. Does that mean using .contains() would produce 10 reads or only 1?
Firestore read count based only on the entire document. Also you are fetching the doc and do .contains() in the client side. So this results in only 1 read.
By the way, you can add in an array without reading the doc. It adds to the array only if it does not have the item.
FirebaseFirestore.instance
.collection('<collection name>')
.doc('<docId>').update({'<arrayFieldKey>':FieldValue.arrayUnion([<new item>])});
Hope it helps!
Related
I would like to create two queries, with pagination option. On the first one I would like to get the first ten records and the second one I would like to get the other all records:
.startAt(0)
.limit(10)
.startAt(9)
.limit(null)
Can anyone confirm that above code is correct for both condition?
Firestore does not support index or offset based pagination. Your query will not work with these values.
Please read the documentation on pagination carefully. Pagination requires that you provide a document reference (or field values in that document) that defines the next page to query. This means that your pagination will typically start at the beginning of the query results, then progress through them using the last document you see in the prior page.
From CollectionReference:
offset(offset) → {Query}
Specifies the offset of the returned results.
As Doug mentioned, Firestore does not support Index/offset - BUT you can get similar effects using combinations of what it does support.
Firestore has it's own internal sort order (usually the document.id), but any query can be sorted .orderBy(), and the first document will be relative to that sorting - only an orderBy() query has a real concept of a "0" position.
Firestore also allows you to limit the number of documents returned .limit(n)
.endAt(), .endBefore(), .startAt(), .startBefore() all need either an object of the same fields as the orderBy, or a DocumentSnapshot - NOT an index
what I would do is create a Query:
const MyOrderedQuery = FirebaseInstance.collection().orderBy()
Then first execute
MyOrderedQuery.limit(n).get()
or
MyOrderedQuery.limit(n).get().onSnapshot()
which will return one way or the other a QuerySnapshot, which will contain an array of the DocumentSnapshots. Let's save that array
let ArrayOfDocumentSnapshots = QuerySnapshot.docs;
Warning Will Robinson! javascript settings is usually by reference,
and even with spread operator pretty shallow - make sure your code actually
copies the full deep structure or that the reference is kept around!
Then to get the "rest" of the documents as you ask above, I would do:
MyOrderedQuery.startAfter(ArrayOfDocumentSnapshots[n-1]).get()
or
MyOrderedQuery.startAfter(ArrayOfDocumentSnapshots[n-1]).onSnapshot()
which will start AFTER the last returned document snapshot of the FIRST query. Note the re-use of the MyOrderedQuery
You can get something like a "pagination" by saving the ordered Query as above, then repeatedly use the returned Snapshot and the original query
MyOrderedQuery.startAfter(ArrayOfDocumentSnapshots[n-1]).limit(n).get() // page forward
MyOrderedQuery.endBefore(ArrayOfDocumentSnapshots[0]).limit(n).get() // page back
This does make your state management more complex - you have to hold onto the ordered Query, and the last returned QuerySnapshot - but hey, now you're paginating.
BIG NOTE
This is not terribly efficient - setting up a listener is fairly "expensive" for Firestore, so you don't want to do it often. Depending on your document size(s), you may want to "listen" to larger sections of your collections, and handle more of the paging locally (Redux or whatever) - Firestore Documentation indicates you want your listeners around at least 30 seconds for efficiency. For some applications, even pages of 10 can be efficient; for others you may need 500 or more stored locally and paged in smaller chucks.
To help me better understand Flutter and Firebase, I'm making a list sharing app. I'm working on the list home screen that will show a reorderable list tile view with a tile for each of the users' lists, I have not began to work on whats inside of these lists. I have firestore set up so that each list is a sub collection, now I want to create a tile for each sub collection in that user's document ( a list of that user's lists). I'm having a tough time telling flutter to do something for each sub collection without using a specific sub collection's name. I wanted to pass in a list title to each tile by making a collection reference for each sub collection( list) and calling .id on each one. Using the collection ID as the title, I'm not yet sure if I can do this or if ill have to make the list title a field inside of each list. Either way, I need to find out how to do something for each subcollection inside a particular document. .forEach seems to only work on document fields, not subcollections? What am I doing wrong? I'm sure there is a better way to go about this. I have not included any code as this is a big picture kind of question.
There is no method in the Firestore client-side SDKs to get all collections (or subcollections under a specific document). Such API does exist in the server-side SDKs, but not in the client-side SDKs.
See:
Fetching all collections in Firestore
How to get all of the collection ids from document on Firestore?
So you'll need to know the collections already, typically by changing your data model. For example by creating a document for each list's metadata, and then storing the list items in a subcollection with a known name under that document. That way you can get all lists by querying for the documents, which is possible within the API.
I have 2 collections. One of them is named "USERS", and the other one "MATCHES". USERS, can join in the MATCHES, appearing the avatar of the user who has joined in the match. The problem is that when the user changes their avatar image after joining in the match, the match avatar doesn't changed, because the match has the old avatar.
The avatar is saved as Base64 in Firestore, but I will change it to "Storage" in the near future.
I have been trying to set the reference, but that only gives me the path.
If I have to do a Database Api Call for each match which is joined the user, maybe I have to do 20 Api calls updating the matches. It can be a solution, but not the best.
Maybe the solution is in the Google Functions?
I'm out of ideas.
Maybe the solution is in the Google Functions?
Cloud Functions also access Firestore through an SDK, so they can't magically do things that the SDK doesn't allow.
If you're duplicating data and you update one of the duplicates, you'll have to consider updating the others. If they all need to be updated, that indeed requires a separate call for each duplicate.
If you don't want to have to do this, don't store duplicate data.
For more on the strategies for updating duplicated data, see How to write denormalized data in Firebase
I need to query my Cloud Firestore database periodically for maintenance. I'm new to REST and I've spent way too long trying to solve this myself, so I figured I could use some advice.
My Firestore is set up like so:
users > {uid} > uploaded-files > {file-hash}
{file-hash} is a document that contains several fields such as filename, source, and size
All I'm trying to do is get a list of every single filename from every single uploaded-file, including from multiple {uid}'s.
I've managed to send a successful request and get a single filename using the firestore.projects.databases.documents.get method using the API explorer, but I can't seem to get any other methods to work, namely firestore.projects.databases.documents.list
This is the successful request using firestore.projects.databases.documents.get:
GET https://firestore.googleapis.com/v1beta1/projects/{project-id}/databases/(default)/documents/users/7eGfdgGfaG0HSXdfmxMN2/uploaded-files/WGtcJBX9fdGdhdtjB?mask.fieldPaths=filename&key={YOUR_API_KEY}
Part of my issue is that I can't figure out how to get requests to work without hard-linking document names - in other words, I don't know how to to replace {uid}, or any other collection, with a wild-card so that the request returns documents from all uid's.
Really any help is greatly appreciated.
The Use the Cloud Firestore REST API documentation has instructions on getting started. The Firestore REST API documentation shows how to fetch documents.
In your case you would need to list the user-uid documents then go after the uploaded-files for each one, or iterate over the results of the list.
I'm pretty confused concerning this hip thing called NoSQL, especially CloudantDB by Bluemix. As you know, this DB doesn't store the values chronologically. It's the programmer's task to sort the entries in case he wants the data to.. well.. be sorted.
What I try to achive is to simply get the last let's say 100 values a sensor has sent to Watson IoT (which saves everything in the connected CloudantDB) in an ORDERED way. In the end it would be nice to show them in a D3.css style kind of graph but that's another task. I first need the values in an ordered array.
What I tried so far: I used curl to get the data via PHP from https://averylongID-bluemix.cloudant.com/iotp_orgID_iotdb_2018-01-25/_all_docs?limit=20&include_docs=true';
What I get is an unsorted array of 20 row entries with random timestamps. The last 20 entries in the DB. But not in terms of timestamps.
My question is now: Do you know of a way to get the "last" 20 entries? Sorted by timestamp? I did a POST request with a JSON string where I wanted the data to be sorted by the timestamp, but that doesn't work, maybe because of the ISO timestamp string.
Do I really have to write a javascript or PHP script to get ALL the database entries and then look for the 20 or 100 last entries by parsing the timestamp, sorting the array again and then get the (now really) last entries? I can't believe that.
Many thanks in advance!
I finally found out how to get the data in a nice ordered way. The key is to use the _design api together with the _view api.
So a curl request with the following URL / attributes and a query string did the job:
https://alphanumerical_something-bluemix.cloudant.com/iotp_orgID_iotdb_2018-01-25/_design/iotp/_view/by-date?limit=120&q=name:%27timestamp%27
The curl result gets me the first (in terms of time) 120 entries. I just have to find out how to get the last entries, but that's already a pretty good result. I can now pass the data on to a nice JS chart and display it.
One option may be to include the timestamp as part of the ID. The _all_docs query returns documents in order by id.
If that approach does not work for you, you could look at creating a secondary index based on the timestamp field. One type of index is Cloudant Query:
https://console.bluemix.net/docs/services/Cloudant/api/cloudant_query.html#query
Cloudant query allows you to specify a sort argument:
https://console.bluemix.net/docs/services/Cloudant/api/cloudant_query.html#sort-syntax
Another approach that may be useful for you is the _changes api:
https://console.bluemix.net/docs/services/Cloudant/api/database.html#get-changes
The changes API allows you to receive a continuous feed of changes in your database. You could feed these changes into a D3 chart for example.