swift：具有博客+多个实体的滑出导航的核心数据

Question

I am making a blog reader app in which the categories of the blog are listed in the slide out navigation and each category fetches unique JSON Results and displays in the CenterViewController

Now, the CenterViewConroller saves the data into CoreData before displaying it in the UITableView with this code:

func animalSelected(animal: Animal) {

var appDel: AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
var context: NSManagedObjectContext = appDel.managedObjectContext!

showProgressHUD()

let session = NSURLSession.sharedSession()
var error : NSError?
 var posts = [[String:String]()]

let task = session.dataTaskWithURL(animal.url!, completionHandler: {data, response, error -> Void in

    if (error != nil){
        println(error)

    }else{

        var request = NSFetchRequest(entityName: "MIBlog")
        request.returnsObjectsAsFaults = false
        var results = context.executeFetchRequest(request, error: nil)

        for result in results!
        {
            context.deleteObject(result as NSManagedObject)
            context.save(nil)

        }


        let jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as NSDictionary

        var post:AnyObject

        var authorDictionary:AnyObject
        var newBlogItem:NSManagedObject
        for var i = 0; i < jsonResult["posts"]!.count; i++
        {
            posts.append([String:String]())
            post = jsonResult["posts"]![i] as NSDictionary
            posts[i]["title"] = post["title"] as? NSString
            posts[i]["publishedDate"] = post["date"] as? NSString
            posts[i]["content"] = post["content"] as? NSString
            authorDictionary = post["author"] as NSDictionary
            posts[i]["author"] = post["name"] as? NSString
            posts[i]["thumbnailURL"] = post["thumbnail"] as? NSString
            posts[i]["postURL"] = post["url"] as? NSString


            newBlogItem = NSEntityDescription.insertNewObjectForEntityForName("MIBlog", inManagedObjectContext: context) as NSManagedObject
            newBlogItem.setValue(posts[i]["title"], forKey: "title")
            newBlogItem.setValue(posts[i]["publishedDate"], forKey: "publishedDate")
            newBlogItem.setValue(posts[i]["content"], forKey: "content")
            newBlogItem.setValue(posts[i]["author"], forKey: "author")
            newBlogItem.setValue(posts[i]["thumbnailURL"], forKey: "thumbnailURL")
             newBlogItem.setValue(posts[i]["postURL"], forKey: "postURL")

             context.save(nil)
        }

       request = NSFetchRequest(entityName: "MIBlog")
        request.returnsObjectsAsFaults = false
   results = context.executeFetchRequest(request, error: nil)

    }   
})

task.resume()

delegate?.collapseSidePanels?()

}

Note: In the code animal.url! is the url of the category fetched

So everytime i select a new category from the slideout navigation, the core data is overwritten with the contents of new category and it takes too much time in loading.

Coming to my question, is it possible to have a unique entity in coredata for each category so that the results dont get overwritten?? Is it advisable to implement something like this??

I am not able to figure that if i fetch all categories in their respective entities, how will i display them all in my same UITableview for CenterViewController?

FetchResultController

// MARK: - Fetched results controller

var fetchedResultsController: NSFetchedResultsController {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
        }
        var appDel: AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        self.managedObjectContext = appDel.managedObjectContext

        let fetchRequest = NSFetchRequest()
        // Edit the entity name as appropriate.
        let entity = NSEntityDescription.entityForName("MIBlog", inManagedObjectContext: self.managedObjectContext!)
        fetchRequest.entity = entity

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

        // Edit the sort key as appropriate.
        let sortDescriptor = NSSortDescriptor(key: "publishedDate", ascending: false)
        let sortDescriptors = [sortDescriptor]

        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: self.managedObjectContext!, sectionNameKeyPath: nil, cacheName: "Master")
        aFetchedResultsController.delegate = self
        _fetchedResultsController = aFetchedResultsController

        var error: NSError? = nil
        if !_fetchedResultsController!.performFetch(&error) {
            // 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.
            //println("Unresolved error \(error), \(error.userInfo)")
            abort()
        }

        return _fetchedResultsController!
}

At my wits end.. plsss pls pls help

Answer 1

Yes, it is possible and it is advisable. Create a relationship between a Category entity and a MIBlog entity. When saving each MIBlog object to Core Data, you should check to see if a category by that name/id exists, and if it exists, use it, and if not, create that category. I use these functions to do so:

func fetchCategory(name: String) -> Category? {

    let fetchRequest = NSFetchRequest(entityName: "Category")
    let predicate = NSPredicate(format: "name = %@", name)

    // Assign fetch request properties
    fetchRequest.predicate = predicate
    fetchRequest.fetchBatchSize = 1
    fetchRequest.fetchLimit = 1

    // Handle results
    let fetchedResults = managedObjectContext?.executeFetchRequest(fetchRequest, error: nil)

    if fetchedResults?.count != 0 {

        if let fetchedCategory: Category = fetchedResults![0] as? Category {
            return fetchedCategory
        }
    }
    return nil
}

func fetchOrCreateCategory(name: String) -> Category {
    if let category = fetchCategory(name) {
        return category
    } else {
        if !name.isEmpty {
            createCategory(name)
            return fetchOrCreateCategory(name)
        } else {
            return fetchOrCreateCategory("Other")
        }
    }
}

Then you can easily retrieve all categories in an array using a fetch request for the categories entity and you can even check to make sure the category actually has blog posts in it.

func fetchCategories() -> [Category] {
    let fetchRequest = NSFetchRequest(entityName: "Category")
    let sortDescriptor = NSSortDescriptor(key: "name", ascending: true)
    let predicate = NSPredicate(format: "blogs.@count != 0") // blogs is whatever you relationship attribute is

    fetchRequest.predicate = predicate
    fetchRequest.sortDescriptors = [sortDescriptor]

    return managedObjectContext?.executeFetchRequest(fetchRequest, error: nil) as! [Category]
}