CODEWITHSUNDEEP
javascriptfirebasegoogle-cloud-firestore
Pascal
Pascal

Reputation: 1751

How to paginate Firestore dataset by individual page?

I want to paginate my forum posts stored in Firebase by pages of 20 items, like so:

and so on.

Now I am aware I can work with query cursors (as mentioned here), which works perfectly fine for e.g. infinite scroll, because there I start with page 1->2->3 and so on, and each time I have the last visible document available to reference to in my .startAfter(lastVisible) method.

But what if I want users to be able to access e.g. page 13 to see posts 241-260 directly? Is there a way to start at page document 241, without doing (multiple) queries first to get the lastVisible documents?

Addition:

This is probably very bad, so be carful in implementing the below. I found following way to "solve" this issue:

const pageNo = 1 /* variable */
const postsPerPage = 20

const baseRef = fireDb.collection("posts")

let currentPageRef

if (pageNo === 1) {
  currentPageRef = baseRef.limit(postsPerPage)

} else {

  let lastVisibleRef = baseRef.limit((pageNo-1) * postsPerPage)
  const lastVisibleQuerySnapshot = await lastVisibleRef.get()
  const lastVisiblePost = lastVisibleQuerySnapshot.docs[lastVisibleQuerySnapshot.docs.length-1]

  currentPageRef = baseRef.startAfter(lastVisiblePost).limit(postsPerPage)
}
const currentPageQuerySnapshot = await currentPageRef.get()

That needs two queries. But it achieves what I want to achieve. Can anyone judge how bad that solution is efficiency/billing? E.g. if someone would access page 999 I fear that will be costly?

Upvotes: 7

Views: 2314

Answers (2)

Ninja Dev
Ninja Dev

Reputation: 826

I'm trying to solve this, and I think a cloud function that runs daily or weekly and assigns each document a manual order might help you

for example, if you want the documents sorted by rating, then the cloud function will run each day, get the documents by their rating, and and assigns the most ranked document order = 1, 2nd document order = 2 ....

this way, you can query documents 1-10 for page 1, query documents 11-20 for page 2 ....

  • the downside is that you will pay the cost of reading and writing to all the documents every day or week
  • you also need to do this manual order for every sort order ( rank, most viewed ... )
  • and you increase the complexity

but if you simply want the results sorted by most recent, then you can simply assign a manual increasing order for each new document

  • and store the newest document order in an info document
  • so if you have a 100 documents
  • and you want the oldest 10 documents, you will simply get documents ordered 1-10

however, given how little I use google search pages and how little I scroll through a youtube search

  • this might not be worth the effort and the cost

good luck

Upvotes: 1

Doug Stevenson
Doug Stevenson

Reputation: 317427

With the Firestore client SDKs, there is no ability to specify an offset into query results. You can read a discussion about this on GitHub.

The server SDKs do have offset, however.

Upvotes: 4

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