swift - NSFetchRequest Order By语法

Question

怎么了伙计们。

我目前正在这样做：

var results = NSArray()
        let appDel = UIApplication.sharedApplication().delegate as! AppDelegate
        let context = appDel.managedObjectContext

        let fetch = NSFetchRequest(entityName: "Work")



        let entity = NSEntityDescription.entityForName("Work", inManagedObjectContext: context)!
        let monthDesc = entity.attributesByName["shortMonth"] as NSAttributeDescription!
        let keyPathExpression  = NSExpression(forKeyPath: "date")
        // Does not really matter
        let countExpression = NSExpression(forFunction: "count:", arguments: [keyPathExpression])
        let expressionDescription = NSExpressionDescription()
        expressionDescription.name = "count"
        expressionDescription.expression = countExpression
        expressionDescription.expressionResultType = .Integer32AttributeType


        fetch.propertiesToFetch = [monthDesc, expressionDescription]
        fetch.propertiesToGroupBy = [monthDesc]
        fetch.resultType = .DictionaryResultType
        //var error: NSError? = nil




        fetch.returnsObjectsAsFaults = false;


        do {
            results = try context.executeFetchRequest(fetch)

        } catch {
            print("Unable to fetch results")
            abort()
        }


        let months = results.flatMap{$0["shortMonth"] as? String}
        let countt = results.flatMap{$0["count"] as? Double}

        print("Months \(months)")
        print("Countt \(countt)")

这将返回两个数组，其中包含月份名称和该月份名称的记录数。

结果：

Months ["Apr", "Feb", "Mar", "May"]
Countt [4.0, 10.0, 12.0, 5.0]

在这个实体中，我还有一个用于monthNumber的属性。

我怎样才能打印出这些按月份编号排序的数组呢？

它现在看起来是按字母顺序排列的。

谢谢

Answer 1

这将完成所要求的操作：

var results = NSArray()
        let appDel = UIApplication.sharedApplication().delegate as! AppDelegate
        let context = appDel.managedObjectContext

        let fetch = NSFetchRequest(entityName: "Work")



        let entity = NSEntityDescription.entityForName("Work", inManagedObjectContext: context)!
        let monthDesc = entity.attributesByName["shortMonth"] as NSAttributeDescription!
        let monthNumber = entity.attributesByName["month"] as NSAttributeDescription!
        let keyPathExpression  = NSExpression(forKeyPath: "date")
        let countExpression = NSExpression(forFunction: "count:", arguments: [keyPathExpression])
        let expressionDescription = NSExpressionDescription()
        expressionDescription.name = "count"
        expressionDescription.expression = countExpression
        expressionDescription.expressionResultType = .Integer32AttributeType

        fetch.propertiesToFetch = [monthDesc, monthNumber, expressionDescription]
        fetch.propertiesToGroupBy = [monthDesc, monthNumber]

        let sortDescriptor = NSSortDescriptor(key: "month", ascending: true)
        let sortDescriptors = [sortDescriptor]
        fetch.sortDescriptors = sortDescriptors
        fetch.resultType = .DictionaryResultType

        fetch.returnsObjectsAsFaults = false;

        do {
            results = try context.executeFetchRequest(fetch)

        } catch {
            print("Unable to fetch results")
            abort()
        }


        let months = results.flatMap{$0["shortMonth"] as? String}
        let countt = results.flatMap{$0["count"] as? Double}

        print("Months \(months)")
        print("Countt \(countt)")

这将同时按monthNumber和monthName进行分组，并将按monthNumber排序，并输出monthName和计数。

输出：

Months ["Jan", "Feb", "Mar", "Apr"]
Countt [3.0, 10.0, 3.0, 10.0]