使用方法预填充核心数据答案

【问题标题】：Pre Populate Core Data with a method使用方法预填充核心数据
【发布时间】：2016-12-07 14:37:34
【问题描述】：

我为我的 Core Data 子类创建了一个扩展，在这里我实现了一个预填充表的方法，首先我检查表中是否有任何内容，然后我插入了一些值，但是当我执行获取：

由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：'executeFetchRequest:error: <null> is not a valid NSFetchRequest.'

import Foundation
import CoreData

extension SimulationParams {

    public static func feedSimulationParams(context: NSManagedObjectContext) {


        let fetchRequest : NSFetchRequest<NSFetchRequestResult>

        if #available(iOS 10.0, *) {
            fetchRequest = SimulationParams.fetchRequest()
        } else {
            fetchRequest = NSFetchRequest(entityName: "SimulationParams")
        }

        let idDescriptor: NSSortDescriptor = NSSortDescriptor(key: "id", ascending: false)
        fetchRequest.sortDescriptors = [idDescriptor]

        fetchRequest.fetchLimit = 1


        var newId = 0;

        do {
            let results = try context.fetch(fetchRequest)

            if(results.count == 0){

                self.setValue(getId(fetchRequest: fetchRequest, context: context), forKeyPath: "id")
                self.setValue(1.5, forKeyPath: "bankFeePercentage")
                self.setValue(1, forKeyPath: "consoMaxMonthly")
                self.setValue(12, forKeyPath: "consoMinMonthly")
                self.setValue(3.5, forKeyPath: "consoRatePercentage")
                self.setValue(4, forKeyPath: "fileFeePercentage")
                self.setValue(1, forKeyPath: "immoMaxMonthly")
                self.setValue(25, forKeyPath: "immoMinMonthly")
                self.setValue(2.05, forKeyPath: "immoRatePercentage")
                self.setValue(3, forKeyPath: "prepaymentPenaltyPercentage")
                self.setValue(1, forKeyPath: "notaryGridId")

                do {
                    try context.save()
                } catch let error as NSError {
                    print ("Error first demande insertion \(error)")
                }
            }


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



    }
}

【问题讨论】：

不相关，但为什么不self.bankFeePercentage = 1.5？你知道...forKeyPath 的真正用途吗？
@vadian 我无法使用 self 访问属性。 forKeyPath，是关于数据库的

标签： swift core-data

【解决方案1】：

解决方案：

警告，您必须在 Data Model Inspector 中删除该模块并将其设置为全局命名空间。

你必须在你的代码上这样做：

    let fetchRequest : NSFetchRequest<NSFetchRequestResult>

    if #available(iOS 10.0, *) {
        fetchRequest = Params.fetchRequest()
    } else {
        fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Params")
    }

    //let predicate = NSPredicate(format: "key=%@", key)
    //fetchRequest.predicate = predicate

    do {
        let results = try context.fetch(fetchRequest)

        if(results.count != 0){

            let params = NSEntityDescription.insertNewObject(forEntityName: "Params", into: context) as! Params

            params.setValue(value, forKey: "value")

            do {
                try context.save()
            } catch let error as NSError {
                print ("Error first demande insertion \(error)")
            }

        } else if (results.count == 0) {

            let params = NSEntityDescription.insertNewObject(forEntityName: "Params", into: context) as! Params

            params.key = key
            params.value = value

            context.insert(params)
        }


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

【讨论】：