我有一个名为 NoteEntity 的核心数据实体(类型)。它有一个名为 noteDocument 的托管变量，它属于自定义类型 NoteDocument(我的 NSDocument 子类)。我更改了它自动生成的 NoteEntity+Core Data Properties 类，所以它显示为

import Foundation
import CoreData

extension NoteEntity {

    @NSManaged var noteDocument: NoteDocument? // changed
    @NSManaged var belongsTo: NSSet?

}

所以 noteDocument 是 NoteDocument 类型而不是 NSObject。 NoteDocument 类确实实现了 NSCoding，如下所示:

required convenience init(coder theDecoder: NSCoder)
{
    let retrievedURL = theDecoder.decodeObjectForKey("URLKey") as! NSURL
    self.init(receivedURL: retrievedURL)
}

func encodeWithCoder(theCoder: NSCoder)
{
    theCoder.encodeObject(fileURL, forKey: "URLKey")
}

我希望能够在托管上下文中找到具有给定 noteDocument 值的 noteEntity 实体。所以我运行这段代码(向它传递一个参数 theNote，该参数对应于我知道托管上下文中存在的 noteDocument):

    var request = NSFetchRequest(entityName: "NoteEntity")
    let notePredicate = NSPredicate(format: "noteDocument == %@", theNote)
    request.predicate = notePredicate

    print("Text in the NoteEntity with the NoteDocument for "+theNote.filename+":")

    do
    {
        let notesGathered = try context.executeFetchRequest(request) as? [NoteEntity]

        for n in notesGathered!
        {
            print (n.noteDocument!.filename)
            print (n.noteDocument!.noteText)
        }
    }
    catch let error as NSError
    {
        print("Could not run fetch request. \(error), \(error.userInfo)")
    }

但它没有返回任何条目。如果我注释掉谓词，我将获得数据库中的所有 NoteEntity 值，但是其中的谓词我什么也得不到。显然我在谓词中尝试进行的搜索有问题。我认为这是因为该值是一个 Transformable，但我不确定从那里去哪里。我知道您不能对 Transformable 数组的成员运行提取请求，但是否不可能对单个 Transformable 属性运行提取请求？如果不是，还有哪些替代方案？

编辑:NoteDocument 类包含的内容比 NSCoding 多得多。正如我所说，它是一个 NSDocument 子类。 NSCoding 使用 URL 作为它的键，因为它是 NoteDocument 类的“主键”——它是初始化类的东西。这是类(class)的其余部分，不包括上面的 NSCoding:

import Cocoa

class NoteDocument: NSDocument, NSCoding
{
var filename: String
var noteText: String
var attributes: NSDictionary?
var dateCreated: NSDate?
var dateString: String?

init (receivedURL: NSURL)
{
    self.filename = ""
    self.noteText = ""
    super.init()

    self.fileType = "net.daringfireball.markdown"
    self.fileURL = receivedURL

    // Try to get attributes, most importantly date-created.
    let fileManager = NSFileManager.defaultManager()
    do
    {
        attributes = try fileManager.attributesOfItemAtPath(fileURL!.path!)
    }
    catch let error as NSError
    {
        print("The error was: "+String(error))
    }

    if let dateCreated = attributes?.fileCreationDate()
    {
        // print("dateCreated is "+String(dateCreated!))

        // Format the date-created to an appropriate string.
        dateString = String(dateCreated)
    }
    else
    {
        print("Did not find the attributes for "+filename)
    }

    if let name = self.fileURL?.lastPathComponent
    {
        filename = name
    }
    else
    {
        filename = "Unnamed File"
    }

    noteText = ""

    do
    {
        noteText = try NSString(contentsOfURL: self.fileURL!, encoding: NSUTF8StringEncoding) as String
    }
    catch let error as NSError
    {
        print("Error trying to get note file:"+String(error))
    }
}

// MARK: - Document functions

override class func autosavesInPlace() -> Bool
{
    // print ("autosavesInPlace ran.")
    return true
}

override func dataOfType(typeName: String) throws -> NSData
{        
    var outError: NSError! = NSError(domain: "Migrator", code: 0, userInfo: nil)

    // Post: Document is saved to a file specified by the user.

    outError = NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)

    if let value = self.noteText.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false) {
        // Convert noteText to an NSData object and return that.
        return value
    }
    print("dataOfType ran.")

    throw outError

}

override func readFromData(data: NSData, ofType typeName: String) throws
{
    // Currently unused; came free with NSDocument.
    throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
}


}

最佳答案

在代码中，您表明您正在编码的唯一内容是 URL。在这种情况下，在实体中使用纯字符串来存储 URL 并为文档添加 transient 属性(或创建包装类以组合实体和文档)更有意义并提供更多实用程序。通过这种方式，您可以在谓词中使用 URL，并且很容易从文档构建谓词。将文档存储为可转换文件并不能以任何方式帮助您。

关于swift - 获取单个 Transformable 属性的请求 (Swift)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38556553/