在Swift中仅初始化一次CoreData实体

import CoreData

class CoreDataManager {
    static let shared = CoreDataManager()
    
    private init() {}
    
    // 懒加载持久化容器
    lazy var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "YourDataModelName")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()
    
    // 获取托管对象上下文
    lazy var managedObjectContext: NSManagedObjectContext = {
        return self.persistentContainer.viewContext
    }()
    
    // 保存上下文
    func saveContext() {
        if managedObjectContext.hasChanges {
            do {
                try managedObjectContext.save()
            } catch {
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }
}

let context = CoreDataManager.shared.managedObjectContext

// 创建实体对象
if let entity = NSEntityDescription.entity(forEntityName: "YourEntityName", in: context) {
    let newObject = NSManagedObject(entity: entity, insertInto: context)
    // 设置属性值
    newObject.setValue("Value1", forKey: "attribute1")
    newObject.setValue("Value2", forKey: "attribute2")
    
    // 保存上下文
    CoreDataManager.shared.saveContext()
}

// 查询实体对象
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "YourEntityName")
do {
    let results = try context.fetch(fetchRequest)
    for data in results as! [NSManagedObject] {
        let attribute1 = data.value(forKey: "attribute1") as? String
        let attribute2 = data.value(forKey: "attribute2") as? String
        print("attribute1: \(attribute1 ?? ""), attribute2: \(attribute2 ?? "")")
    }
} catch {
    print("Fetch failed: \(error.localizedDescription)")
}

// 更新实体对象
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "YourEntityName")
fetchRequest.predicate = NSPredicate(format: "attribute1 == %@", "Value1")
do {
    let results = try context.fetch(fetchRequest)
    if let objectToUpdate = results.first as? NSManagedObject {
        objectToUpdate.setValue("NewValue", forKey: "attribute2")
        CoreDataManager.shared.saveContext()
    }
} catch {
    print("Fetch failed: \(error.localizedDescription)")
}

// 删除实体对象
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "YourEntityName")
fetchRequest.predicate = NSPredicate(format: "attribute1 == %@", "Value1")
do {
    let results = try context.fetch(fetchRequest)
    if let objectToDelete = results.first as? NSManagedObject {
        context.delete(objectToDelete)
        CoreDataManager.shared.saveContext()
    }
} catch {
    print("Fetch failed: \(error.localizedDescription)")
}