Swift / IOS：访问存储在NSSet中的对象

我有两个模态，如下所示的Patient和PatientDocument

@objc (Patient)
class Patient: NSManagedObject {
@NSManaged var id: Int64
    @NSManaged var fullName: String
    @NSManaged var lastVisitDate: NSTimeInterval
    @NSManaged var documents: NSSet
}

@objc (PatientDocument)
class PatientDocument: NSManagedObject {

    @NSManaged var id: Int64
    @NSManaged var documentType: String
    @NSManaged var documentUUID: String
    @NSManaged var patient: Patient
}

我为患者和文档插入了一些虚拟数据并将它们链接起来，一个患者可以拥有许多文档（一对多关系）。在我的应用程序（IOS）上，我具有母版详细信息布局，母版上具有“患者”，而“详细信息”部分上具有“ PatientDocuments”。我想要的是在选择一位患者时显示一位患者的相关文档。

使用prepareforSegue，我可以将选定的患者传递给documentsViewcontroller（一个处理文档的控制器）。在cellForRowAtIndexPath中显示文档时，我在检索该患者的相关文档时遇到了麻烦。

有没有一种方法可以单独检索与所选患者相关的文档？我尝试打印患者体内的NSSet文档，它提供了以下输出。

Optional(Relationship 'documents' on managed object (0x79807af0) <Patient: 0x79807af0> (entity: Patient; id: 0x79808e70 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/Patient/p2> ; data: {
    careTeamMember = "0x79786680 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/Account/p2>";
    documents =     (
        "0x7967d260 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientDocument/p12>",
        "0x7968c0e0 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientDocument/p8>",
        "0x7967d540 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientDocument/p9>"
    );
    fullName = Patient3;
    id = 2;
    isCPO = 1;
    lastVisitDate = "2001-01-01 00:08:55 +0000";
    questionnaire =     (
        "0x79689e00 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientQuestionnaire/p2>",
        "0x7968f440 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientQuestionnaire/p5>",
        "0x796a72a0 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientQuestionnaire/p3>"
    );
}) with objects {(
    <PatientDocument: 0x796a6300> (entity: PatientDocument; id: 0x7967d260 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientDocument/p12> ; data: <fault>),
    <PatientDocument: 0x79694bf0> (entity: PatientDocument; id: 0x7968c0e0 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientDocument/p8> ; data: <fault>),
    <PatientDocument: 0x7967f410> (entity: PatientDocument; id: 0x7967d540 <x-coredata://A7367643-744D-417B-BECE-734260B90D9B/PatientDocument/p9> ; data: <fault>)
)})

（忽略输出中的调查表NSSet，患者与另一个包含不同类型文档的类似对象（称为调查表）相关）