Chapter 6. Working with databases and table views

published book

This chapter covers

Storing and getting data
Using data in table views
Navigating view hierarchies
Changing data model

You’re nearly done with FlashCards. So far, you have applied modelview-controller (MVC) to design a complex app. Then, you learned how to use Interface Builder to draw views and Xcode to code classes. Finally, you added icons, image buttons, backgrounds, and animations to polish up your app.

Next, you’ll learn how to store and fetch data so you can track results. Then your users can see how they have progressed at learning state capitals.

Keeping track of data in the FlashCards app

The purpose of the FlashCards app is to help people remember facts. Whether you’re trying to learn college football mascots, celebrity couples, dog breeds, or multiplication tables, it won’t matter much if you don’t improve. To help your users know how well they’re doing, you need to keep track of their results.

Deciding what to store

The best way to figure out what information to store is to think about what users will want to see later. If you’re using FlashCards to learn something, you at least want to know how long the game took you and when you played.

Figure 6.1. What to store for a game result

You also want to know how you did on each card for a particular game.

Figure 6.2. What to store for a card result

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Sketching how the app will look

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Figure 6.3. Sketch of the new home screen

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Figure 6.4. Sketches of the history screens

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Designing new models

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Figure 6.5. `GameResult` and `CardResult` classes

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Figure 6.6. `FCViewController's showHistory` action

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Figure 6.7. `FCResultViewController`’s `saveGame` message

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Figure 6.8. The sequence of messages when saving a game

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Figure 6.9. `FCGameHistoryViewController` messages

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Figure 6.10. `FCCardHistoryViewController` messages

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Introducing Core Data

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Creating a data model

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Figure 6.11. Making a Data Model in the New File dialog

Name the data model FlashCards .xcdatamodeld.

Figure 6.12. Naming the data model

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Figure 6.13. Data model editor

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Adding entities and attributes

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Figure 6.14. Adding attributes

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Figure 6.15. Configuring parameters in the Data Model Editor

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Figure 6.16. Creating a CardResult entity in the editor

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Using relationships

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Figure 6.17. Defining a relationship in the Data Model Editor

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Generating data classes

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Figure 6.18. Creating a managed object in the New File dialog

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Figure 6.19. Choose the entities to generate code for

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Adding Core Data support to your app

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Figure 6.20. Adding the Core Data Framework

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Figure 6.21. The main Core Data concepts and how they work together

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Object Model

The object representation of the model data resource file.

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Persistent Store Coordinator

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Object Context

Keeps track of changes until they’re saved to the database.

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Managed Objects

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@property (nonatomic, strong) NSPersistentStoreCoordinator *dataStore;
@property (nonatomic, strong) NSManagedObjectModel* dataModel;
@property (nonatomic, strong) NSManagedObjectContext* dataContext;

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#import <CoreData/CoreData.h>

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Listing 6.1. FCAppDelegate.m: creates a persistent store

Figure 6.22. The object model and the persistent store coordinator

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Listing 6.2. FCAppDelegate.m: configuring Core Data

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Figure 6.23. Persistent store coordinator and object context

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Saving your game results

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Figure 6.24. Saving managed objects into the context

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#import <CoreData/CoreData.h>

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-(NSError*)save:(NSManagedObjectContext *)context;

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Listing 6.3. FCGame.m: saving a game’s result

Figure 6.25. Managed objects and the object context

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Listing 6.4. FCCard.m: creating a `CardResult` from a `Card` object

-(CardResult*)cardResultInGame:(GameResult*)gameResult
                   withContext:(NSManagedObjectContext*) context
{
    CardResult* cardResult = [NSEntityDescription
                    insertNewObjectForEntityForName:@"CardResult"
                    inManagedObjectContext:context];
    cardResult.cardName = self.cardText;
    cardResult.wasCorrect = [NSNumber numberWithBool: self.isCorrect];

    return cardResult;
}

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To call these messages, add this message to FCResultViewController.m.

Listing 6.5. FCResultViewController.m: saving a game

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Fetching and viewing data

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Viewing in a table

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Figure 6.26. Creating a `UIViewController`

This time, make it a UITableViewController subclass. Name it FCGameHistoryViewController.m.

Figure 6.27. Making your view controller a subclass of `UITableViewController`

When you’re done, add another view controller for FCCardHistory ViewController.m.

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Figure 6.28. The interaction between the table view controller and Core Data objects to fetch data

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Figure 6.29. Interaction between the table view controller and Core Data objects to show data

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Change FCGameHistoryViewController.h to look like this.

Listing 6.6. FCGameHistoryViewController.h: fetched-results property

Ae vcd zn NSFetchedResultsController, kpd pqz c etroppry ync mxcx z egelatde . Erv’a rvzv c ecrosl vfev sr bvw rvy gtaedeel oskrw.

Figure 6.30. Delegates and protocols with fetched results

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Listing 6.7. FCGameHistoryViewController.m: fetching and sorting entity objects

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Listing 6.8. FCGameHistoryViewController.m: fetching the entity

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Listing 6.9. FCGameHistoryViewController.m: setting up the nav bar with `viewDidLoad`

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Jn viewDidLoad, uxh vcr vgr ilett pnz Unxx bottun nuc xcfu vrb rpsz.

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Figure 6.31. The sequence of messages for showing data in a table

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- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [[self.resultsController sections] count];
}

- (NSInteger)tableView:(UITableView *)tableView
     numberOfRowsInSection:(NSInteger)section
{
    return [[[self.resultsController sections] objectAtIndex:section]
            numberOfObjects];
}

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Listing 6.10. FCGameHistoryViewController.m: filling a cell

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Listing 6.11. FCGameHistoryViewController.m: making a cell for the given row

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Rup s ttnbuo vr PBLjwxBlotoelrnr.jye kjof rkg kznk egq zbxx reeth daelyar.
Wcoo nc ttleou cedall showHistoryBtn, nyz entcnoc rj.
Wxvs zn ctonai ldealc showHistory, hns necotnc rj.
Keapdt animateViewLoad rwqj vrb wkn unttbo.
Deatdp viewDidLoad rwjd prx nwo ubnott.

Hxtx’a drx svyk kr gbnri dg our tsihyro dsiien c agniivtoan clleorntro.

Listing 6.12. FCViewController.m: showing history

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Xhn qrx dckm, bnc vp er brk ythsroi khzb rx vck sighotnme ejkf yjar.

Figure 6.32. Game result history in the simulator

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Navigating to related data

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To use it, add a results property to FCCardHistoryViewController.h:

@property(strong, nonatomic) NSArray *results;

Now, implement the two section- and row-count messages:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView
        numberOfRowsInSection:(NSInteger)section
{
    return [self.results count];
}

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Listing 6.13. FCCardHistoryViewController.m: filling a cell

Bbn xgh ckng arju essgame ervewehn yuk’ot desak xr dirovep c ofsf.

Listing 6.14. FCCardHistoryViewController.m: getting a cell for this row

- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellId = @"Cell";
    UITableViewCell *cell =
       [tableView dequeueReusableCellWithIdentifier:CellId];
    if (cell == nil) {
        cell = [[UITableViewCell alloc]
                 initWithStyle:UITableViewCellStyleSubtitle
                 reuseIdentifier:CellId];
    }
    [self fillCell:cell withResultAtIndexPath: indexPath];
    return cell;
}

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Mxbn c GameResult ja doutche, kdq atnvgiea rv ruo ssut thiorsy. Yhp vrp fiowlongl egsames re ETOsmoHisoyrtEjkwRlnrtroole.m.

Listing 6.15. FCGameHistoryViewController.m: navigating to the card history

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Figure 6.33. Card result history in the simulator

Changing your data model

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Versioning your data model

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The green check mark shows you the current version.

Figure 6.34. Setting the current data model version

Figure 6.35. Ensuring that the latest version is correct

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Migrating between versions

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Planning for what’s next

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