在swift中提取相关表3

我试图获取属于某品牌的所有模型，但是当我试图获取外键时，我得到了一种NSSET类型，它带有一些内部具有外键的地址结构的，我坚持，这是我的代码：在swift中提取相关表3

class func insertNew (brandDescription: String, inManagedObjectContext context: NSManagedObjectContext) -> Car_Brand? { 
     let request: NSFetchRequest<Car_Brand> = Car_Brand.fetchRequest() 
     request.predicate = NSPredicate (format: "brand = %@", brandDescription) 
     if let brand = (try? context.fetch(request))?.first { 
      return brand 
     } else if let brand = NSEntityDescription.insertNewObject(forEntityName: "Car_Brand", into: context) as? Car_Brand { 
      brand.brand = brandDescription 
      return brand 
     } 
     return nil 
    } 
class func fetchModel (brandDescription: String, inManagedObjectContext context: NSManagedObjectContext) -> [String]? { 
    let Brand = Car_Brand.insertNew(brandDescription: brandDescription, inManagedObjectContext: context) 
    let request: NSFetchRequest<Model> = Model.fetchRequest() 
    request.predicate = NSPredicate(format: "id_model = %ld", (Brand?.id_model)!) 
    request.propertiesToFetch = ["model"] 
    request.sortDescriptors = [NSSortDescriptor(key: "model", ascending: true)] 
    if let preModelList = try? context.fetch(request) as [Model] { 
     var modelList: [String] = [] 
     for preModelList in preModelList { 
      modelList.append(preModelList.model!) 
     } 
     return modelList 
    } else { 
     return nil 
    } 
}

你能帮助我，请理解如何获取相关表？

来源

2016-11-06 Lester Arévalo

您的fetchModel会在您每次打电话时插入一个新的Car_Brand实例。新插入的实例上不存在任何现有模型是不太可能的。

P.S.它们不是Core Data中的“表格”。我们有实体和关系。但是将核心数据视为数据库会让您随时遇到很多逻辑问题。

来源

2016-11-06 21:25:45

谢的，只有插入，如果不存在，我试图修改谓词这样的事情，request.predicate = NSPredicate（格式： “Car_Brand.id_model =％@”，brandDescription），但也不起作用，你知道我在哪里可以找到一些很好的例子来过滤这种方式 –

解决方案：

class func fetchModel (brandDescription: String, inManagedObjectContext context: NSManagedObjectContext) -> [String]? { 
     let request: NSFetchRequest<Model> = Model.fetchRequest() 
     request.predicate = NSPredicate(format: "id_model.brand = %@",brandDescription) 
     request.propertiesToFetch = ["model"] 
     request.sortDescriptors = [NSSortDescriptor(key: "model", ascending: true)] 
     if let preModelList = try? context.fetch(request) as [Model] { 
      var modelList: [String] = [] 
      for preModelList in preModelList { 
       modelList.append(preModelList.model!) 
      } 
      return modelList 
     } else { 
      return nil 
     } 
    }

参考： https://developer.apple.com/library/prerelease/content/documentation/Cocoa/Conceptual/Predicates/Articles/pUsing.html

来源

2016-11-06 21:47:47

在swift中提取相关表3

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