核心数据一对多关系在创建新关系时被删除
Core Data one-to-many relationship gets deleted when creating a new one
我是 Core Data 的新手,在探索它的工作方式时,我发现自己陷入了另一个问题。
我从两个单独的 Web 服务获取数据,一个获取 JSON 员工列表,另一个获取 JSON 公司列表。
公司将其员工列为 employeeID 数组,而员工将其工作的公司列为逗号分隔字符串,不作为参考。
所以我是这样做的:
1) 我确保从空数据库开始
2) 我从员工源中填充我的核心数据
3) 我填充我的公司实体,设置与他们拥有的每个员工的关系(这就是问题所在)
4) 我想显示公司及其关联员工的列表
问题是,一个公司可以雇佣几个员工,每个员工可以为0到n个企业工作。
因此,当我创建我的第一家公司时,我 link 它给它的员工并且一切正常,但是当我创建我的第二家公司并且 link 它给前一家公司的员工时,前一家公司失去了它与该员工的关系。
经过一些研究,我没有发现类似的问题(可能是因为我还是一个核心数据新手我没有找对地方),但我发现了这个post:
http://codekea.com/3J1AZNYRkAMr/setting-core-data-relationship-reusing-same-object-removes-previous-relation.html
这似乎是完全相同的问题。
由于答案在我的案例中没有解决任何问题(代码将不再编译),我想我会创建一个示例项目来说明它。
该项目可以从这里下载测试:
https://www.dropbox.com/s/qi65sh52wwe6ws3/test.zip?dl=0
我的代码如下(我用的是SwiftyJSON):
let mURLEmployees = NSURL(string: "http://pastebin.com/raw.php?i=ZhmHCmwQ")
let mURLCompanies = NSURL(string: "http://pastebin.com/raw.php?i=LCbvyvqv")
override func viewDidLoad() {
super.viewDidLoad()
//==============================================
// 1)
// EMPTY THE DATABASE
//==============================================
var error: NSError? = nil
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let context = appDelegate.managedObjectContext!
let request = NSFetchRequest(entityName: "Employee")
let entities = context.executeFetchRequest(request, error: nil) as! [NSManagedObject]
for entity in entities {
context.deleteObject(entity)
}
let request2 = NSFetchRequest(entityName: "Company")
let entities2 = context.executeFetchRequest(request2, error: nil) as! [NSManagedObject]
for entity in entities2 {
context.deleteObject(entity)
}
if !context.save(&error) {
println("An error occured while deleting entities : \(error?.localizedDescription)")
}
//==============================================
// 2)
// POPULATE EMPLOYEES
//==============================================
let entityEmployee = NSEntityDescription.entityForName("Employee", inManagedObjectContext: context)
let JSONEmployeesString = NSString(contentsOfURL: mURLEmployees!, encoding: NSUTF8StringEncoding, error: &error) as! String
var dataJSON = JSONEmployeesString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
var json = JSON(data: dataJSON!)
if let employees = json["features"].array {
for employee in employees {
let employeeObject = Employee(entity: entityEmployee!, insertIntoManagedObjectContext: context)
employeeObject.name = employee["properties"]["NAME"].string!
employeeObject.companies = employee["properties"]["COMPANIES"].string!
if !context.save(&error) {
println("An error occured while saving employees : \(error?.localizedDescription)")
}
}
}
//==============================================
// 3)
// POPULATE COMPANIES
//==============================================
let JSONCompaniesString = NSString(contentsOfURL: mURLCompanies!, encoding: NSUTF8StringEncoding, error: &error) as! String
dataJSON = JSONCompaniesString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
json = JSON(data: dataJSON!)
if let companies = json["features"].array {
for company in companies {
let employees = company["properties"]["EMPLOYEES"].array!
var employeeObjects = NSMutableSet()
for employee in employees {
let predicateEmployeeName = NSPredicate(format: "name == %@", employee.string!)
let DBRequestEmployeeObject = NSFetchRequest(entityName: "Employee")
DBRequestEmployeeObject.predicate = predicateEmployeeName
let EmployeeResultArray = context.executeFetchRequest(DBRequestEmployeeObject, error: nil) as! [Employee]
if let EmployeeResult = EmployeeResultArray.first {
employeeObjects.addObject(EmployeeResult)
} else {
println("ERROR")
}
}
let entityCompany = NSEntityDescription.entityForName("Company", inManagedObjectContext: context)
let companyObject = Company(entity: entityCompany!, insertIntoManagedObjectContext: context)
companyObject.name = company["properties"]["NAME"].string!
companyObject.employees = employeeObjects
if !context.save(&error) {
println("An error occured while saving companies : \(error?.localizedDescription)")
}
}
}
//==============================================
// 4)
// RESULT
//==============================================
let requestCompanies = NSFetchRequest(entityName: "Company")
let companies = context.executeFetchRequest(requestCompanies, error: nil) as! [Company]
println("Number of companies : \(companies.count)")
for company in companies {
println("\(company.name)")
for employee in company.employees {
println("->\(employee.name)")
}
}
}
我的数据模型如下所示:
你的关系是多对多的,在你的 Employee managedObject 中你需要有 "companies" 关系而不是属性。那么你必须重新生成你的托管对象子类。
然后在不设置公司关系的情况下创建所有员工实体(使用您的循环)。
然后创建公司,并在为每个公司创建公司时获取员工,然后将他们添加到公司 companyObject.employees = employeeObjects
我是 Core Data 的新手,在探索它的工作方式时,我发现自己陷入了另一个问题。
我从两个单独的 Web 服务获取数据,一个获取 JSON 员工列表,另一个获取 JSON 公司列表。 公司将其员工列为 employeeID 数组,而员工将其工作的公司列为逗号分隔字符串,不作为参考。
所以我是这样做的:
1) 我确保从空数据库开始
2) 我从员工源中填充我的核心数据
3) 我填充我的公司实体,设置与他们拥有的每个员工的关系(这就是问题所在)
4) 我想显示公司及其关联员工的列表
问题是,一个公司可以雇佣几个员工,每个员工可以为0到n个企业工作。 因此,当我创建我的第一家公司时,我 link 它给它的员工并且一切正常,但是当我创建我的第二家公司并且 link 它给前一家公司的员工时,前一家公司失去了它与该员工的关系。
经过一些研究,我没有发现类似的问题(可能是因为我还是一个核心数据新手我没有找对地方),但我发现了这个post: http://codekea.com/3J1AZNYRkAMr/setting-core-data-relationship-reusing-same-object-removes-previous-relation.html 这似乎是完全相同的问题。 由于答案在我的案例中没有解决任何问题(代码将不再编译),我想我会创建一个示例项目来说明它。
该项目可以从这里下载测试: https://www.dropbox.com/s/qi65sh52wwe6ws3/test.zip?dl=0
我的代码如下(我用的是SwiftyJSON):
let mURLEmployees = NSURL(string: "http://pastebin.com/raw.php?i=ZhmHCmwQ")
let mURLCompanies = NSURL(string: "http://pastebin.com/raw.php?i=LCbvyvqv")
override func viewDidLoad() {
super.viewDidLoad()
//==============================================
// 1)
// EMPTY THE DATABASE
//==============================================
var error: NSError? = nil
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let context = appDelegate.managedObjectContext!
let request = NSFetchRequest(entityName: "Employee")
let entities = context.executeFetchRequest(request, error: nil) as! [NSManagedObject]
for entity in entities {
context.deleteObject(entity)
}
let request2 = NSFetchRequest(entityName: "Company")
let entities2 = context.executeFetchRequest(request2, error: nil) as! [NSManagedObject]
for entity in entities2 {
context.deleteObject(entity)
}
if !context.save(&error) {
println("An error occured while deleting entities : \(error?.localizedDescription)")
}
//==============================================
// 2)
// POPULATE EMPLOYEES
//==============================================
let entityEmployee = NSEntityDescription.entityForName("Employee", inManagedObjectContext: context)
let JSONEmployeesString = NSString(contentsOfURL: mURLEmployees!, encoding: NSUTF8StringEncoding, error: &error) as! String
var dataJSON = JSONEmployeesString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
var json = JSON(data: dataJSON!)
if let employees = json["features"].array {
for employee in employees {
let employeeObject = Employee(entity: entityEmployee!, insertIntoManagedObjectContext: context)
employeeObject.name = employee["properties"]["NAME"].string!
employeeObject.companies = employee["properties"]["COMPANIES"].string!
if !context.save(&error) {
println("An error occured while saving employees : \(error?.localizedDescription)")
}
}
}
//==============================================
// 3)
// POPULATE COMPANIES
//==============================================
let JSONCompaniesString = NSString(contentsOfURL: mURLCompanies!, encoding: NSUTF8StringEncoding, error: &error) as! String
dataJSON = JSONCompaniesString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
json = JSON(data: dataJSON!)
if let companies = json["features"].array {
for company in companies {
let employees = company["properties"]["EMPLOYEES"].array!
var employeeObjects = NSMutableSet()
for employee in employees {
let predicateEmployeeName = NSPredicate(format: "name == %@", employee.string!)
let DBRequestEmployeeObject = NSFetchRequest(entityName: "Employee")
DBRequestEmployeeObject.predicate = predicateEmployeeName
let EmployeeResultArray = context.executeFetchRequest(DBRequestEmployeeObject, error: nil) as! [Employee]
if let EmployeeResult = EmployeeResultArray.first {
employeeObjects.addObject(EmployeeResult)
} else {
println("ERROR")
}
}
let entityCompany = NSEntityDescription.entityForName("Company", inManagedObjectContext: context)
let companyObject = Company(entity: entityCompany!, insertIntoManagedObjectContext: context)
companyObject.name = company["properties"]["NAME"].string!
companyObject.employees = employeeObjects
if !context.save(&error) {
println("An error occured while saving companies : \(error?.localizedDescription)")
}
}
}
//==============================================
// 4)
// RESULT
//==============================================
let requestCompanies = NSFetchRequest(entityName: "Company")
let companies = context.executeFetchRequest(requestCompanies, error: nil) as! [Company]
println("Number of companies : \(companies.count)")
for company in companies {
println("\(company.name)")
for employee in company.employees {
println("->\(employee.name)")
}
}
}
我的数据模型如下所示:
你的关系是多对多的,在你的 Employee managedObject 中你需要有 "companies" 关系而不是属性。那么你必须重新生成你的托管对象子类。
然后在不设置公司关系的情况下创建所有员工实体(使用您的循环)。 然后创建公司,并在为每个公司创建公司时获取员工,然后将他们添加到公司 companyObject.employees = employeeObjects