核心数据 NSPredicate 按数组中的项目过滤项目集

Question

所以我有一个与 GameGenre 具有一对多关系的 SavedGames 实体。每个游戏可以有多个流派。我的关系如下所示。现在，我希望从一系列流派名称中按流派名称进行过滤。

有些游戏可能只有单一类型，例如“运动”，而其他游戏可能包含多种类型，例如“运动”、“模拟”。我想获取任何游戏，其中可能包含数组内的任何类型名称。因此，例如，如果数组仅包含“Sport”。如果 gameA 有“Sport”，gameB 有“Sport”、“Simulation”，gameC 有“Simulation”、“Racing”，我想 return gameA 和 gameB。

我尝试了几个谓词，到目前为止只成功地 return 将单个游戏对象设置为“运动”类型，但还 return 我知道包含的其他对象“运动”。我如何配置我的谓词以获得我正在寻找的东西？到目前为止我已经尝试过：

NSPredicate(format: "ANY genreType.name IN %@", argumentArray: [genres])

NSPredicate(format: "SUBQUERY(%K, $genre, ANY $genre.name IN %@) .@count > 0" , #keyPath(SavedGames.genreType), genres)

NSPredicate(format: "SUBQUERY(%K, $genre, $genre.name = %@) .@count > 0", #keyPath(SavedGames.genreType), genres)

                    var predicateArr : [NSPredicate] = []
                    for genre in genres {
                        let predicate = NSPredicate(format: "ANY %K.name = %@",argumentArray: [#keyPath(SavedGames.genreType), genre])
                        predicateArr.append(predicate)
                    }
                    let compoundArr = NSCompoundPredicate(orPredicateWithSubpredicates: predicateArr)

这是我用来获取游戏的方法：

    func fetchGame<T: NSManagedObject>(_ objectType: T.Type, sortBy: String? ,platformID: Int?, selectedGenres: [String]?, selectedPlatforms: [Int]?) -> [T]{
        var entityName = String(describing: objectType)
        var fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
        var filterPredicate : NSPredicate?
        var sortAscending : NSSortDescriptor?
        var platforms : [Int] = []
        var genres : [String] = []
        if let platform = selectedPlatforms{
        platforms = platform
        }
        if let genre = selectedGenres {
            genres = genre
        }

        if let sortKey = sortBy {
            
            sortAscending = NSSortDescriptor(key: sortKey, ascending: true)
        } else {
            sortAscending = NSSortDescriptor(key: "title", ascending: true)
        }

      
        
                print("selectedPlatform is", platforms)
                print("selectedGenre is", genres)
                
                switch (platforms.isEmpty, genres.isEmpty) {

                case (true, true):
                    // both arrays are empty so we don't filter anything and return all SavedGame objects

                    print("both arrays are empty so we don't filter anything and return all SavedGame objects")
                    filterPredicate = NSPredicate(value: true)

                    
                case (true, false):
                    // only filter genres

                    print("only filter genres")
                    
                    filterPredicate = NSPredicate(format: "SUBQUERY(%K, $genre, $genre.name IN %@).@count > 0", #keyPath(SavedGames.genreType), genres)


                case (false, true):
                    // only filter platforms

                    print("only filter platforms")
                    filterPredicate = NSPredicate(format: "%K in %@", argumentArray: [#keyPath(SavedGames.platformID), platforms])

                    
                case (false, false):
                    // filter both genres and platforms


                    print("filter both genres and platforms")
                    filterPredicate = NSCompoundPredicate(andPredicateWithSubpredicates: [
                        NSPredicate(format: "ANY genreType.name == %@", argumentArray:  [genres]),
                       
                        NSPredicate(format: "%K IN %@", argumentArray: [#keyPath(SavedGames.platformID), platforms])
                    ])
                }


            print("filterPredicate", filterPredicate)
                
                fetchRequest.predicate = filterPredicate
                fetchRequest.sortDescriptors = [sortAscending!]
                
         

   

        do {
            let fetchedObjects = try context.fetch(fetchRequest) as? [T]
            return fetchedObjects ?? [T]()
        } catch {
            print("error")
            return [T]()
        }
    
        
        
    }

Answer 1

问题在于反向关系是一对一的：如果您只有一个“运动”类型，并将其分配给多个 SavedGames，则只会保留最后一个 - link其他 SavedGames 将被删除。所以你的谓词工作正常。

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