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swift - FetchedResultsController 使用谓词排除集合中包含的结果

问题描述

我正在尝试过滤 FetchedResultsController 中的项目以过滤掉一组项目。这些是引擎，其中有特定的字母名称，后跟数字。名称中可能的字母范围是从“A”到“O”。我希望能够根据另一个条件过滤掉名称从“D”到“O”的引擎。

我设置了一个常量“highPowerEngines”，它是一个包含这些字母的集合。由于该名称仅包含一个字母，因此我想排除任何包含 highPowerEngines 中任何字母的名称。到目前为止，这是我的代码，我正在处理的谓词包含在 FIXME 之后：

func configureFetchedResultsController() {
    let context = databaseController.getContext()
    let enginesFetchRequest = NSFetchRequest<Engine>(entityName: CoreData.engine)
    let highPowerEngines: Set =  ["D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O"]

    var predicate = NSPredicate()
    if currentStage == 1 && stages! == 1 {
        predicate = NSPredicate(format: "engineType == %@", EngineType.singleStage.rawValue)
    } else if currentStage < stages! {
        predicate = NSPredicate(format: "engineType == %@", EngineType.boosterStage.rawValue)
    } else {
        predicate = NSPredicate(format: "engineType == %@", EngineType.upperStage.rawValue)
    }

    var predicateArray:[NSPredicate] = [
        predicate
        ]
    // FIXME: Sort out highPowerEngines
    if !dPlusEngineIAP {
        if currentStage == 1 && stages! == 1 {
            predicate = NSPredicate(format: "NOT engineDesignation CONTAINS %@", highPowerEngines)
            predicateArray.append(predicate)
        }
    }

    let compoundPredicate = NSCompoundPredicate(andPredicateWithSubpredicates: predicateArray)
    enginesFetchRequest.predicate = compoundPredicate

    let primarySortDescriptor = NSSortDescriptor(key: CoreData.isMadeByName, ascending: true)
    let secondarySortDescriptor = NSSortDescriptor(key: CoreData.engineDesignation, ascending: true)
    enginesFetchRequest.sortDescriptors = [primarySortDescriptor, secondarySortDescriptor]


    self.fetchedResultsController = NSFetchedResultsController<Engine>(
        fetchRequest: enginesFetchRequest,
        managedObjectContext: context,
        sectionNameKeyPath: CoreData.isMadeByName,
        cacheName: nil)

    self.fetchedResultsController.delegate = self

}

标签： swiftcore-dataswift4

解决方案

感谢这里的帖子：CoreData Predicate get every sentence that contains any word in array ，我终于能够解决我的问题。我当前的工作代码在这里：

func configureFetchedResultsController() {
    let context = databaseController.getContext()
    let enginesFetchRequest = NSFetchRequest<Engine>(entityName: CoreData.engine)
    let lowPowerEngines =  ["A", "B", "C"]

    var predicate = NSPredicate()
    if currentStage == 1 && stages! == 1 {
        predicate = NSPredicate(format: "engineType == %@", EngineType.singleStage.rawValue)
    } else if currentStage < stages! {
        predicate = NSPredicate(format: "engineType == %@", EngineType.boosterStage.rawValue)
    } else {
        predicate = NSPredicate(format: "engineType == %@", EngineType.upperStage.rawValue)
    }

    var predicateArray:[NSPredicate] = [
        predicate
        ]

    if !dPlusEngineIAP {
        let predicates = lowPowerEngines.map {
            NSPredicate(format: "engineDesignation CONTAINS %@", $0)
        }
        let predicate = NSCompoundPredicate(orPredicateWithSubpredicates: predicates)
            predicateArray.append(predicate)
    }

    let compoundPredicate = NSCompoundPredicate(andPredicateWithSubpredicates: predicateArray)
    enginesFetchRequest.predicate = compoundPredicate

    let primarySortDescriptor = NSSortDescriptor(key: CoreData.isMadeByName, ascending: true)
    let secondarySortDescriptor = NSSortDescriptor(key: CoreData.engineDesignation, ascending: true)
    enginesFetchRequest.sortDescriptors = [primarySortDescriptor, secondarySortDescriptor]


    self.fetchedResultsController = NSFetchedResultsController<Engine>(
        fetchRequest: enginesFetchRequest,
        managedObjectContext: context,
        sectionNameKeyPath: CoreData.isMadeByName,
        cacheName: nil)

    self.fetchedResultsController.delegate = self

}

处理数组中每个项目的解决方案是使用 map 函数创建一个复合谓词。然后将复合谓词添加到 fetchedResultsController。这让我可以比较引擎，看看它是否在 lowPowerEngines 中。Map 为 lowPowerEngines 中的每个项目创建一个单独的谓词。我什至可以即时以编程方式更改它。我真的希望这对某人有所帮助，因为没有中心位置可以提出这些技巧。当我收集到足够的它们时，我会做一个主帖。

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