ios - 核心数据关系问题

Question

我的核心数据面临一个奇怪的问题。我有以下关系

一个联系人可以属于一个类别，一个类别可以有多个联系人。我想在创建联系人时访问联系人中的我的类别。我的关系正确吗？

我收到以下错误“无法分配“字符串”类型的值!在此字段中“类别”类型的值: newContact.category = CategoryField.text

这就是我尝试访问我的类别字段的方式:

// MARK: - Properties
    var contact: Contact?   

func createCategory() {
        let entity = NSEntityDescription.entityForName("Category", inManagedObjectContext: context!)
        let category = Category(entity: entity!, insertIntoManagedObjectContext: context)
        let index = pickerView.selectedRowInComponent(0)
        let color = categoryColor[index]

            category.name = name.text
            category.descript = descriptionField.text
            category.color = color
            println(category.name)
            context?.save(nil)
        name.text = ""
        descriptionField.text = ""
    }

     func createNewContact() {
    let entity = NSEntityDescription.entityForName("Contact", inManagedObjectContext: context!)
            let newContact = Contact(entity: entity!, insertIntoManagedObjectContext: context)
                newContact.name = nameField.text
                newContact.email = emailField.text
                newContact.phone = phoneField.text
                newContact.category = categoryField.text
                newContact.photo = UIImageJPEGRepresentation(imageHolder.image, 1)

            var error: NSError?

            context?.save(&error)
    }

And that's how my entities look like: 

    @objc (Contact)
    class Contact: NSManagedObject {

        @NSManaged var email: String
        @NSManaged var name: String
        @NSManaged var phone: String
        @NSManaged var photo: NSData
        @NSManaged var category: Category

    }

和

@objc (Category)
class Category: NSManagedObject {

    @NSManaged var color: AnyObject
    @NSManaged var descript: String!
    @NSManaged var name: String!
    @NSManaged var contact: NSOrderedSet

}

Answer 1

Contact 对象的 category 属性是一个 Category 对象。但您试图将其设置为字符串(categoryField.text)。您可能想要使用 name 等于 categoryField.text 的 Category 对象。

您可以创建一个:

    let categoryEntity = NSEntityDescription.entityForName("Category", inManagedObjectContext: context!)
    let newCategory = Category(entity: categoryEntity!, insertIntoManagedObjectContext: context)
    newCategory.name = categoryField.text
    // set the other properties for the Category as necessary
    // then assign the relationship
    newContact.category = newCategory

但您可能已经使用该名称创建了一个类别。因此，通常的方法是搜索具有正确名称的类别，如果存在则使用该类别，如果不存在则创建一个新类别:

    let categoryEntity = NSEntityDescription.entityForName("Category", inManagedObjectContext: context!)
    let fetchRequest = NSFetchRequest()
    fetchRequest.entity = categoryEntity!
    fetchRequest.predicate = NSPredicate(format:"name == %@",categoryField.text)
    let fetchResults = try? context!.executeFetchRequest(fetchRequest)
    if let results = fetchResults {
        var requiredCategory : Category
        if (results.count > 0) {
            requiredCategory = results[0] as! Category
        } else {
            requiredCategory = Category(entity: categoryEntity!, insertIntoManagedObjectContext: context!)
            requiredCategory.name = categoryField.text
            // set the other properties for the Category as necessary
        }
        newContact.category = requiredCategory
    }