为何CoreData预加载生成重复条目而非唯一实体？

我想在视图首次加载且无成就条目时，向CoreData预加载成就数据，每个成就都是唯一的Achievements实体，后续用户达成成就时只更新completed属性。但现在虽然能生成正确数量的条目，却全是重复值。

实现代码 #

import SwiftUI
import CoreData

struct AchievementView: View {
    
    @Environment(\.managedObjectContext) private var viewContext
    @FetchRequest(entity: Achievements.entity(), sortDescriptors: [
        NSSortDescriptor(key: "id", ascending: true)])
      private var achievements: FetchedResults<Achievements>


    var body: some View {
        NavigationView {
            ZStack {
                Color("Background")
                    .ignoresSafeArea(.all)
                VStack {
                    HStack {
                        let completedCount = achievements.filter(\.completed).count
                        let totalCount = achievements.count
                        let pctComp: Double = (Double(completedCount) / Double(totalCount)) * 100
                        
                        Image(systemName: "star.circle").padding(.leading, 5)
                            .foregroundColor(.secondary)
                        Text("Achievements".uppercased())
                            .fontWeight(.heavy)
                            .foregroundColor(.secondary)
                        Spacer()
                        Text("\(completedCount) OF \(totalCount) (\(pctComp, specifier: "%.f")%)")
                            .font(.system(size:16))
                            .fontWeight(.heavy)
                            .foregroundColor(.secondary)
                            .padding(.trailing, 10)
                    }
                    ScrollView(showsIndicators: false) {
                        VStack {
                            ForEach(achievements) { achievement in
                                HStack {
                                    VStack {
                                        if achievement.completed == false {
                                            Text(achievement.image ?? "")
                                                .padding()
                                                .grayscale(0.99)
                                                .overlay (
                                                    Circle()
                                                        .stroke(Color(.systemGray6), lineWidth: 2)
                                                ).padding()
                                        } else {
                                            Text(achievement.image ?? "")
                                                .padding()
                                                .overlay (
                                                    Circle()
                                                        .stroke(Color.green, lineWidth: 2)
                                                ).padding()
                                        }
                                    }
                                    VStack{
                                        if achievement.completed == false {
                                            HStack {
                                                Text(achievement.name ?? "")
                                                    .fontWeight(.heavy)
                                                    .foregroundColor(Color(.systemGray2))
                                                Spacer()
                                            }
                                            HStack {
                                                Text(achievement.desc ?? "")
                                                    .fontWeight(.light)
                                                    .font(.system(size:10))
                                                    .foregroundColor(Color(.systemGray2))
                                                Spacer()
                                            }
                                        } else {
                                            HStack {
                                                Text(achievement.name ?? "")
                                                    .fontWeight(.heavy)
                                                Spacer()
                                            }
                                            HStack {
                                                Text(achievement.desc ?? "")
                                                    .fontWeight(.light)
                                                    .font(.system(size:10))
                                                Spacer()
                                            }
                                        }
                                    }
                                    Spacer()
                                }   .background(Color("WeekShowBack"))
                                    .cornerRadius(15)
                            }
                        }
                    }
                }.padding()
            }
        }.navigationViewStyle(StackNavigationViewStyle())
            .onAppear(perform: loadAchievements)
    }
    
    private func loadAchievements() {
        
        print("Number of Times Called")
        let achievementNames = ["First Entry", "Movie Starter"]
        let achievemnetDesc = ["Enter your first movie or show", "Track 10 Movies"]
        let achievementComp = [false, false]
        let achievementImage = ["🥇","🔟"]
        
        if achievements.count == 0 {
            
            for index in 0..<achievementNames.count {
                let newAchievement = Achievements(context: self.viewContext)
                newAchievement.name = achievementNames[index]
                newAchievement.desc = achievemnetDesc[index]
                newAchievement.completed = achievementComp[index]
                newAchievement.image = achievementImage[index]
                
                do {
                    try viewContext.save()
                    print("Achievement Loaded!!!!!!")
                } catch let error {
                    print(error)
                }
            }
        }
    }
        
}

问题截图 #

解决方案 #

问题根源 #

1. 缺少唯一标识：Achievements实体未设置唯一id属性，FetchRequest按id排序但该字段未赋值，导致CoreData无法区分不同实体，ForEach渲染时出现重复。
2. 多次保存上下文：循环内每次创建实体都调用save()，触发多次UI刷新，加剧了重复显示的问题。

修复步骤 #

1. 给实体添加唯一id
   打开CoreData模型文件，给Achievements实体新增id属性：

   • 类型选择UUID
   • 勾选「Use scalar type」选项

2. 修改预加载方法
   调整loadAchievements，给每个新成就分配唯一id，并统一保存上下文：

   private func loadAchievements() {
       print("Number of Times Called")
       let achievementNames = ["First Entry", "Movie Starter"]
       let achievemnetDesc = ["Enter your first movie or show", "Track 10 Movies"]
       let achievementComp = [false, false]
       let achievementImage = ["🥇","🔟"]
       
       guard achievements.count == 0 else { return }
       
       for index in 0..<achievementNames.count {
           let newAchievement = Achievements(context: self.viewContext)
           newAchievement.id = UUID() // 赋值唯一ID
           newAchievement.name = achievementNames[index]
           newAchievement.desc = achievemnetDesc[index]
           newAchievement.completed = achievementComp[index]
           newAchievement.image = achievementImage[index]
       }
       
       // 循环结束后一次性保存
       do {
           try viewContext.save()
           print("所有成就加载完成!!!!!!")
       } catch let error {
           print(error)
       }
   }
   

3. 让实体遵守Identifiable协议
   在Achievements+CoreDataProperties.swift中添加协议扩展：

   extension Achievements: Identifiable {
   }
   

   这样ForEach可以通过id正确识别每个实体的唯一性，避免重复渲染。

内容的提问来源于stack exchange，提问作者user20715683