ios - 核心数据 - 基于参数插入

Question

我有一个名为 Person 的表。如何创建一个基于名称的数据条目，而不是重复名称。

例子:

I have a person named Josh. Can not have another person named Josh.

类似PK的功能。

Answer 1

不幸的是，CoreData 没有内置的方法来防止重复。

首先，使用谓词执行获取请求以查看该值是否存在。如果不存在，则插入新实体。

示例)

    let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
    let managedContext = appDelegate.managedObjectContext!
    let personName = "Josh"

    let fetchRequest = NSFetchRequest(entityName: "Person")
    let predicate = NSPredicate(format: "name = %@", personName)
    fetchRequest.predicate = predicate

    var error: NSError?
    let fetchedResults = managedContext.executeFetchRequest(fetchRequest, error: &error) as [NSManagedObject]?

    if let results = fetchedResults {
        // if no results found, then insert
        if results.count == 0 {
            let entity =  NSEntityDescription.entityForName("Person", inManagedObjectContext: managedContext)
            let person = Person(entity: entity!, insertIntoManagedObjectContext:managedContext)
            person.setValue(personName, forKey: "name")

            var error: NSError?
            if !managedContext.save(&error) {
                println("Could not save \(error), \(error?.userInfo)")
            }
        }

    } else {
        println("Could not fetch \(error), \(error!.userInfo)")
    }