如何修改SwiftUI+Firebase代码实现帖子按条件排序？

我正在开发基于Firebase的SwiftUI应用，当前帖子按发布日期降序排序。现在需要将upPostPlusDay数组非空的帖子优先展示，其余帖子仍按发布日期排序。

修改思路 #

• 实现两级排序逻辑：第一优先级为upPostPlusDay是否非空（非空帖子靠前），第二优先级为发布日期（降序）
• 推荐使用Firestore端排序（性能更优）：新增一个存储字段标记数组是否非空，让Firestore直接按该字段和发布日期排序
• 若不想修改数据库结构，可选择本地排序，但分页逻辑会存在局限性

修改后的Post模型代码 #

import SwiftUI
import FirebaseFirestoreSwift

struct Post: Identifiable, Codable, Equatable, Hashable {
    @DocumentID var id: String?
    var text: String
    var postHead: String
    var postAddress: String
    var imageURL: URL?
    var imageReferenceID: String = ""
    var publishedDate: Date = Date()
    var likedIDs: [String] = []
    var dislikedIDs: [String] = []
    var plusFavorites: [String] = []
    var upPostPlusDay: [Int] = []
    // 新增存储字段：标记upPostPlusDay是否非空，需在创建帖子时赋值为!upPostPlusDay.isEmpty
    var hasUpPostPlusDay: Bool = false
    var userName: String
    var userUID: String
    var userProfileURL: URL
    var userBioLink: String
    
    enum CodingKeys: CodingKey {
        case id
        case text
        case postHead
        case postAddress
        case imageURL
        case imageReferenceID
        case publishedDate
        case likedIDs
        case dislikedIDs
        case plusFavorites
        case upPostPlusDay
        case hasUpPostPlusDay
        case userName
        case userUID
        case userProfileURL
        case userBioLink
    }
}

方案一：Firestore端排序（推荐） #

修改fetchPosts方法，让Firestore先按hasUpPostPlusDay降序（非空帖子靠前），再按发布日期降序排序：

func fetchPosts() async {
    do {
        var query: Query!
        if let paginationDoc {
            query = Firestore.firestore().collection("Posts")
                .order(by: "hasUpPostPlusDay", descending: true)
                .order(by: "publishedDate", descending: true)
                .start(afterDocument: paginationDoc)
                .limit(to: 5)
        } else {
            query = Firestore.firestore().collection("Posts")
                .order(by: "hasUpPostPlusDay", descending: true)
                .order(by: "publishedDate", descending: true)
                .limit(to: 5)
        }
        
        if basedOnUID {
            query = query.whereField("userUID", isEqualTo: uid)
        }
        
        let docs = try await query.getDocuments()
        let fetchedPosts = docs.documents.compactMap { doc -> Post? in
            try? doc.data(as: Post.self)
        }
        await MainActor.run(body: {
            posts.append(contentsOf: fetchedPosts)
            
            paginationDoc = docs.documents.last
          
            isFetching = false
        })
    } catch {
        print(error.localizedDescription)
    }
}

注意：使用此方案需确保所有已有帖子都更新hasUpPostPlusDay字段，且后续创建帖子时需设置该字段为!upPostPlusDay.isEmpty。

方案二：本地排序（无需修改数据库） #

若不想改动数据库，可在获取帖子后在本地排序，修改fetchPosts中的MainActor代码块：

await MainActor.run(body: {
    let combinedPosts = posts + fetchedPosts
    // 本地排序：非空帖子优先，再按发布日期降序
    let sortedPosts = combinedPosts.sorted {
        if $0.upPostPlusDay.isEmpty != $1.upPostPlusDay.isEmpty {
            return !$0.upPostPlusDay.isEmpty
        } else {
            return $0.publishedDate > $1.publishedDate
        }
    }
    posts = sortedPosts
    
    paginationDoc = docs.documents.last
  
    isFetching = false
})

注意：本地排序会导致分页逻辑异常（Firestore仍按原规则分页），仅适合数据量较小的场景。

内容的提问来源于stack exchange，提问作者avldokuchaev