Question

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，它是自定义类型NoteDocument（我的NSDocument的子类）。我更改了自动生成的NoteEntity + Core Data Properties类，使其读取

import Foundation
import CoreData

extension NoteEntity {

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

}

因此noteDocument的类型为NoteDocument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（传递一个参数theNote，它对应于我知道在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)")
    }

但它不返回任何条目。如果我注释掉谓词，我会在数据库中获得所有NoteEntity值，但是在那里使用谓词我什么也得不到。很明显，我在谓词中试图做的搜索有问题。我认为它是因为价值是可转换的，但我不知道从那里去哪里。我知道你不能对Transformable数组的成员运行获取请求，但是不可能在单个Transformable属性上运行获取请求吗？如果不是，还有哪些替代方案？

编辑：NoteDocument类包含的内容远远多于NSCoding。正如我所说，它是一个NSDocument子类。 NSCoding使用URL作为其密钥，因为它是＆＃34;主键＆＃34;对于NoteDocument类 - 它是初始化类的原因。这是本课程的其余部分，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)
}


}

Answer 1

在代码中，您显示您编码的唯一内容是网址。在这种情况下，它更有意义，并提供更多实用程序来在实体中使用普通字符串来存储URL并为文档添加瞬态属性（或创建包装类来组合实体和文档）。通过这种方式，您可以在谓词中使用URL，并且可以轻松地从文档构建谓词。将文档存储为可转换文件并不能以任何方式帮助您。

获取单个Transformable属性的请求（Swift）

1 个答案: