【iOS】【CoreData】（二）

概述
一、创建一个 Entity
二、Entity 的增删改查

一、创建一个 Entity
1、首先打开 .xcdatamodeld 文件，点击下方的 Add Entity 按钮，添加一个 Entity，命名为 Person
2、为 Person 添加两个 Attribute 分别为 Integer 16 类型的 age，String 类型的 name，如下图所示

屏幕快照 2019-07-03 下午2.39.56.png

3、创建一个 Person 对象

        let entity = NSEntityDescription.entity(forEntityName: "Person", in: container.viewContext)!
        let person = NSManagedObject(entity: entity, insertInto: nil) as! Person
        return p

二、Entity 的增删改查

    // 增
    class func insert(_ obj: NSManagedObject) -> Void {
        shared.container.viewContext.insert(obj)
    }
    
    // 删
    class func delete(_ obj: NSManagedObject) -> Void {
        shared.container.viewContext.delete(obj)
    }
    
    // 改
    class func update(_ obj: NSManagedObject) -> Void {
        shared.container.viewContext.refresh(obj, mergeChanges: true)
    }
    
    // 查
    class func fetchPerson() -> [Person] {
        let request: NSFetchRequest<Person> = NSFetchRequest(entityName: "Person")
        do {
            let result = try shared.container.viewContext.fetch(request)
            return result
        } catch {
            fatalError("fetch Person error: \(error)")
        }
    }

使用了增、删、改方法后，需要调用 saveContext() 方法将数据保存

    class func saveContext() -> Void {
        let context = shared.container.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                fatalError("Save context error: \(error)")
            }
        }
    }

完整的 CoreDataManager

class CoreDataManager {
    
    static let shared = CoreDataManager()
    
    lazy var container: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "SwiftCoreDataTest")
        container.loadPersistentStores { (description, error) in
            if let error = error {
                fatalError("Unable to load persistent stores: \(error)")
            }
        }
        return container
    }()
    
    private init() {
        
    }
    
    class func saveContext() -> Void {
        let context = shared.container.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                fatalError("Save context error: \(error)")
            }
        }
    }
    
    class func person() -> Person {
        let entity = NSEntityDescription.entity(forEntityName: "Person", in: shared.container.viewContext)!
        let p = NSManagedObject(entity: entity, insertInto: nil) as! Person
        return p
    }
    
    // 增
    class func insert(_ obj: NSManagedObject) -> Void {
        shared.container.viewContext.insert(obj)
    }
    
    // 删
    class func delete(_ obj: NSManagedObject) -> Void {
        shared.container.viewContext.delete(obj)
    }
    
    // 改
    class func update(_ obj: NSManagedObject) -> Void {
        shared.container.viewContext.refresh(obj, mergeChanges: true)
    }
    
    // 查
    class func fetchPerson() -> [Person] {
        let request: NSFetchRequest<Person> = NSFetchRequest(entityName: "Person")
        do {
            let result = try shared.container.viewContext.fetch(request)
            return result
        } catch {
            fatalError("fetch Person error: \(error)")
        }
    }
    
}