How can I display user-interest posts first in an iOS feed without excluding other posts?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I'm using Swift with Firebase Firestore to implement a paginated feed where posts matching a user's interest categories are prioritized and shown first, while still displaying posts outside these categories afterward.

My current implementation fetches the current user, extracts their interest categories, and then builds a query that filters posts based on these categories (if available), orders them by timestamp, and paginates the results. Below is the code I have so far:

SWIFT
static func fetchFeedPostsWithPagination(lastDocument: DocumentSnapshot?, limit: Int) async throws -> (posts: [Post], lastDocument: DocumentSnapshot?) {
        
        let uid = Auth.auth().currentUser?.uid
        let currentUser = try await UserService.fetchUser(withUid: uid ?? "")
        let userCategories = currentUser.categories?.keys.map { $0 } ?? []  // Convert keys to an array
        
        var query: Query = postsCollection
        
        if !userCategories.isEmpty {
            query = query.whereField("category", in: userCategories)
        }
        
        query = query.order(by: "timestamp", descending: true)
        
        query = query.limit(to: limit)
        
        if let lastDocument = lastDocument {
            query = query.start(afterDocument: lastDocument)
        }
        
        let snapshot = try await query.getDocuments()
        var posts = try snapshot.documents.compactMap { try $0.data(as: Post.self) }
        
        for i in 0 ..< posts.count {
            let ownerUid = posts[i].ownerUid
            let postUser = try await UserService.fetchUser(withUid: ownerUid)
            posts[i].user = postUser
        }
        
        let lastDoc = snapshot.documents.last
        return (posts, lastDoc)
    }

I would like to know the best approach to modify or extend this implementation so that it prioritizes posts matching the user's interests without completely filtering out posts that don't match. Any suggestions or adjustments are appreciated.

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

Below is a breakdown of how the provided code works:

Explanation

Fetch Current User & Categories
The function first retrieves the current Firebase Authentication user’s ID and fetches the corresponding user document. It then extracts the keys from the user's categories (if any) to form an array. This array is used to filter posts so that only those matching the user's categories are queried.
Building the Firestore Query
- Conditional Filtering:
  If the user has any categories, the query is filtered using:
```
SWIFT
query = query.whereField("category", in: userCategories)
```
- Ordering:
  The posts are then ordered by the "timestamp" field in descending order:
```
SWIFT
query = query.order(by: "timestamp", descending: true)
```
- Limiting Results:
  The query limits the number of documents returned:
```
SWIFT
query = query.limit(to: limit)
```
- Pagination:
  If a lastDocument exists, the query starts after this document so that the next set of posts is retrieved:
```
SWIFT
if let lastDocument = lastDocument {
    query = query.start(afterDocument: lastDocument)
}
```
Fetching Documents
The code then asynchronously fetches the documents that match the built query:
```
SWIFT
let snapshot = try await query.getDocuments()
```

Mapping to Model Objects
Each document is decoded to a Post object:

SWIFT
var posts = try snapshot.documents.compactMap { try $0.data(as: Post.self) }

Fetching Additional Data
For each post, the code fetches the post owner's user data and assigns it to the user property of the Post:

SWIFT
for i in 0 ..< posts.count {
    let ownerUid = posts[i].ownerUid
    let postUser = try await UserService.fetchUser(withUid: ownerUid)
    posts[i].user = postUser
}

Pagination Handling
The last document from the snapshot is stored and returned along with the posts. This can be used as the starting point for the next paginated query:
```
SWIFT
let lastDoc = snapshot.documents.last
return (posts, lastDoc)
```

Summary

This function efficiently handles paginated loading of "feed posts" by:

Filtering posts based on the current user’s categories.
Sorting posts by timestamp in descending order.
Limiting the number of posts per query.
Fetching the next batch using the last retrieved document as a starting point.
Enriching each post with its owner’s user data.

This approach ensures that your feed is loaded incrementally and only shows posts relevant to the user.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by MeteorExplorer162 • 1 month ago

You can't use a single query to get both the posts that the user is interested in and those that don't match their interests; the two query criteria are opposite.

Since you want to show the "interesting" posts first, followed by the remainders, you can use two queries.

First, request posts with query.whereField("category", in: userCategories)
Once you have retrieved all of these documents, then you can issue a new query query.whereField("category", notIn: userCategories) - You can be sure that none of these documents were in the initial query.

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How can I display user-interest posts first in an iOS feed without excluding other posts?

2 Answers

Explanation

Summary

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