在Swift中从CoreData中获取几列

Question

假设名为 TBL_person 的表格有4列，而我想获取仅 id 和名称列的数据

在SQL中我可以这样做：

  

SELECT id，name FROM TBL_person ORDER BY id ASC

但是在SWIFT可以做些什么？

    let appDel:AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let moContext:NSManagedObjectContext = appDel.managedObjectContext

    let fetchRequest = NSFetchRequest()

    let entityDescription = NSEntityDescription.entityForName("TBL_person", inManagedObjectContext: moContext)

    fetchRequest.entity = entityDescription

    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "id", ascending: true)]

    do {
        let personList = try moContext.executeFetchRequest(fetchRequest) as! [ModelPerson]

        print("test------", personList.count)

    } catch {
        let fetchError = error as NSError
        print(fetchError)
    }

Answer 1

谢谢@Martin R.您的评论帮助我解决了问题。如有必要，可供其他人使用：

let entityDescription = NSEntityDescription.entityForName("TBL_person", inManagedObjectContext: moContext)

    fetchRequest.entity = entityDescription

    fetchRequest.propertiesToFetch = ["id","name"]
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "id", ascending: true)]

    do {
        let personList = try moContext.executeFetchRequest(fetchRequest) as! [ModelPerson]

        print("test------", personList.count)

    } catch {
        let fetchError = error as NSError
        print(fetchError)
    }

Answer 2

我在Core Data Programming Guide中找到了结果。希望能帮到你。 https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/FetchingObjects.html#//apple_ref/doc/uid/TP40001075-CH6-SW1

过滤结果

获取对象的真正灵活性在于获取请求的复杂性。首先，您可以向获取请求添加NSPredicate对象，以缩小返回的对象数。例如，如果您只想要具有FirstName Trevor的Employee对象，则将谓词直接添加到NSFetchRequest：

OBJECTIVE-C

NSString *name = @"Trevor";
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"name == %@", name]];

SWIFT
let name = "Trevor"
fetchRequest.predicate = NSPredicate(format: "name == %@", name)

除了缩小要返回的对象外，还可以配置返回这些对象的方式。例如，您可以指示Core Data返回NSDictionary实例，而不是完全形成的NSManagedObject实例。此外，您可以配置NSFetchRequest，以便这些NSDictionary实例仅包含Employee实体上可用属性的子集。