如何在 Swift 中使用 UISearchBar 和 NSFetchedResultsController 在 Core Data 上一次获取多个实体？

Question

大家好，我有一个使用 Core Data 和 NsFetchedResultsController 的应用程序，我正在使用 searchBar 来搜索 3 个实体中的属性。

问题自然是每个实体都有不同的属性。但我想使用来自用户的相同 searchBar 输入一次搜索所有 3 个实体。

所有 3 个实体都有一个属性“name”，其想法是搜索所有在“name”属性中包含 searchBar 字符串的实体。

到目前为止，我只能搜索 1 个实体，因为我正在使用此代码：

// MARK: - Fetched results controller
var fetchedResultsController: NSFetchedResultsController {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
    }

    let fetchRequest = NSFetchRequest()
    // Edit the entity name as appropriate.

     let entity = NSEntityDescription.entityForName("Category", inManagedObjectContext: moc)
    fetchRequest.entity = entity

    // Set the batch size to a suitable number.
    fetchRequest.fetchBatchSize = 20

    // Edit the sort key as appropriate.
    let sortDescriptor = NSSortDescriptor(key: "index", ascending: true)

    fetchRequest.sortDescriptors = [sortDescriptor]

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)
    aFetchedResultsController.delegate = self
    _fetchedResultsController = aFetchedResultsController

    do {
        try _fetchedResultsController!.performFetch()
    } catch {
        // Replace this implementation with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        //print("Unresolved error \(error), \(error.userInfo)")
        abort()
    }

    return _fetchedResultsController!
}


// MARK: - Search
var searchController: UISearchController? = nil

func reloadFRC(predicate: NSPredicate?) {
    fetchedResultsController.fetchRequest.predicate = predicate
    performFecth()
}

//Delegate: UIsearchController
func updateSearchResultsForSearchController(searchController: UISearchController) {
    if let searchBarText = searchController.searchBar.text {
        var predicate: NSPredicate?
        if searchBarText != "" {
            predicate = NSPredicate(format: "name contains[cd] %@", searchBarText)
        }
        self.reloadFRC(predicate)
    }
}


//Delegate: UISearchBar
func searchBarTextDidEndEditing(searchBar: UISearchBar) {
    self.reloadFRC(nil)
}


//Configure Search
func configureSearch() {
    self.searchController = UISearchController(searchResultsController: nil)
    if let _searchController = self.searchController {
        _searchController.delegate = self
        _searchController.searchResultsUpdater = self
        _searchController.dimsBackgroundDuringPresentation = false
        _searchController.searchBar.delegate = self
        _searchController.searchBar.sizeToFit()
        _searchController.searchBar.barTintColor = Utils.colorFromHex(0x2FC5DA)
        _searchController.searchBar.tintColor = Utils.colorFromHex(0x585858)
        self.tableView.tableHeaderView = _searchController.searchBar
    } else {print("ERROR configuring _searchController in %@", #function)}
}

那么，我该怎么做呢？

Answer 1

不再需要使用_fetchedResultsController，它几乎与所有 Swift 编码风格背道而驰。此外，您可以替换 nil 检查并改用 lazy 修饰符。您是否有特定的原因要使其成为 lazy 而不仅仅是正常初始化它？如果这是一个搜索屏幕，似乎 99.9% 的时间它都会被初始化。

现在谈谈您的实体问题。使所有 3 个实体都继承自一个父实体。此父实体将包含 name 属性。然后，您将获取父实体，它将正确搜索所有子实体。

您还可以通过为NSFetchedResultsController 初始化函数的.sectionNameKeyPath 传入entity.name 来按实体划分它们。如果你决定走这条路，你还需要按entity.name 排序，所以它知道如何对这些部分进行排序。