Core Data iOS Essentials E-Book

Bintu Harwani

• Herausgeber: Packt Publishing
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 373

Veröffentlichungsjahr: 2011

Beschreibung

Core Data is the essential ingredient in data driven iOS apps. It's used for storing, retrieving, and manipulating application data in databases, XML, and binary formats. It's an essential component for iPhone, iPod Touch, and iPad apps.Core Data Essentials provides a clear, readable guide to the most useful aspects of Core Data. Built around a realistic example app, the book showcases the most important aspects of Core Data development in the context of a complete, functioning app written in Objective C.The book starts with a tour of how the app works. Then you'll see how to easily display data using the Table View. You'll learn how to develop an appropriate data model that fits the needs of your app, then implement that model as updatable data objects. You'll see how to update data and build relationships between objects and learn how Core Data can work with search, and how to provide your users with friendly data editing features.

Leseprobe

Table of Contents

Core Data iOS Essentials

Credits

About the Author

Acknowledgement

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers, and more

Why Subscribe?

Free Access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Overview

Prerequisite

A brief history

Enterprise Object Framework (EOF)

Core Data

Why use Xcode?

Source code

Shall we begin?

2. Understanding Core Data

Core Data

Core Data features

Data Model

Entities

Properties

Attributes

Relationships

Inverse relationship

Model View Controller (MVC)

Core Data API

Persistent Store

Persistent Store Coordinator

FetchRequest

FetchedResultsController

Overview of the application: Sales Record System for a Departmental Store

Entity Relationship Diagram

An application output sample

Entering Master Product Information

Modifying the Master Product

Deleting the Master Product

Entering customer information and order details

Deleting customer information

Searching for specific customers

Searching and modifying customer information

Entering Customer Sales Information

Automatic Master Product Update

Summary

3. Understanding Objective-C Protocol and Table View

Protocol

Implementing the Strategy pattern

Defining the protocol

Creating a delegate property

Declaring protocol methods

Creating a sample application using a protocol and a delegate

Adding the ViewController class for entering numerical values

Defining the protocol, outlets, and action methods in the SecondViewController.h header file

Defining the SecondViewController class and connecting controls

Invoking delegate methods from the SecondViewController.m implementation file

Declaring the delegate, outlet, and action methods in the demodelegateViewController.h header file

Defining the demodelegateViewController and connecting controls

Implementing the protocol methods in the demodelegateViewController.m file

Running the project

Introduction to Table View

Creating an application to display Table View cells

Declaring an array in the header file

Implementing UITableViewDataSource protocol methods

Adding names to the Table View

Adding the AddNameController View controller

Defining protocols, outlets, and action methods in the AddNameController.h header file

Defining the AddNameController class View and connecting controls

Invoking Delegate methods in the AddNameController.m implementation file

Invoking the AddNameController View and implementing the protocol methods

Placing and connecting the Bar Button Item control in the RootViewController

Summary

4. Designing a Data Model and Building Data Objects for Customers

Creating a new project

Designing the data model

Data Model Editor

Adding an entity

Adding an attribute property

Types of attributes

Fields applying constraints

Building data objects for the Customer entity

Understanding code of autogenerated files

Header file of Application Delegate

Implementation file of Application Delegate

applicationWillTerminate method

managedObjectContext method

managedObjectModel method

persistentStoreCoordinator method

applicationDocumentsDirectory method

Summary

5. Creating, Listing, and Deleting Names of Customers

Splitting the task into two modules

Creating a module to save and delete a customer's name

Using the ViewController class for adding the name of the customer

Defining protocol, outlets, and action methods in the header file

Defining the View of the AddNameController class and connecting controls

Invoking delegate methods from the implementation file

Declaring delegate and implementing methods for storing the name of the customers

Key value coding (KVC)

Key value methods

The -valueForKey: method

The -setValue:forKey: method

Keypath

Implementing the methods of the NSFetchedResultsControllerDelegate protocol

The controllerWillChangeContent method

The controllerDidChangeContent method

The controller:didChangeObject method

The controller:didChangeSection method

Running the project

Summary

6. Creating, Listing, Displaying, and Deleting Records of Customers

Understanding multiple managed object context

NSNotification

Applying the concept of multiple managed object context in our application

Enhancing our application to save, list, display, and delete customer information

Adding the ViewController class

Defining a View for entering the customer's information and connecting controls

Coding in the implementation file for accepting the customer's information and invoking delegate methods

Adding the View Controller class for displaying the customer's information

Defining the View and writing the code in the implementation file for displaying the customer's information

Implementing the methods in the RootViewController class for storing the customer's information

viewDidLoad method

cell AtIndexPath method

didSelectRowAtIndexPath method

addCustomer method

addcustomerController method

Viewing the project

Summary

7. Updating and Searching Records of Customers

Applying the update feature

Defining a protocol in the DisplayCustomerController class

Adding Edit button to enable modifications in the View of DisplayCustomerController class

Implementing the protocol's method for storing modified customer information

Using KVO to know what has been updated

Running the project

Applying search facility

Defining outlet of UISearchBar class in the header file of the RootViewController class

Placing the Search Bar control in the View of RootViewController and specifying its delegate

Implementing delegate method in the RootViewController class to apply searching

Understanding NSPredicate

Removing the keyboard after selecting a customer's name

Using Predicate Builder for creating a search criterion

Fetched properties

Fetch request templates

Building and accessing a fetch request without a variable

Building and accessing a fetch request with a variable

Summary

8. Entering, Saving, Listing, and Deleting the Records of the Products Sold to the Customers

Adding the product entity to the Data Model

Relationship

Types of relationships

One to one relationship

One to many relationship

Many to many relationship

Establishing a relationship between the Customer and the Product entities

Setting a relationship from the Customer entity to the Product entity

Delete rule

Setting a relationship from the Product entity to the Customer entity (inverse relationship)

Building the data object for the Customer and the Product entities

Understanding the role of the auto generated special methods of a relationship

Entering the information of the products sold to the customers

Creating a module to develop an interface to enter the product information

Adding a ViewController class for entering the information of the products sold to the customers

Defining the protocol, outlets, and action methods in the header file

Designing the View of the AddProductController class and connecting the controls

Invoking the delegate methods from the implementation file

Developing a module to create a menu for manipulating the product information

Adding a ViewController class to display the Product's menu to manipulate the product's information

Defining the outlets and action methods in the header file

Designing the View of a ProductInfoController class and connecting the controls

Coding in the implementation file to save, edit, and display the product's information

Creating a module to connect the Product's menu to the rest of the project

Defining the outlets and action methods in the header file

Adding a Toolbar control to the View of the DisplayCustomerController class

Coding in the implementation file to invoke the View of the ProductInfoController class

Running the project

Summary

9. Entering, Displaying, and Deleting the Stock

Adding the MasterProduct entity to the Data Model

Storing the image of the MasterProduct

Transformable data type

The Value Transformer Name: field

Creating a value transformer

Building the data object for the MasterProduct entity

Maintaining the MasterProduct information

Image Picker

Adding custom images to the Image Picker

Making an image appear within a given size

Module to develop interface to enter the information of the MasterProduct

Adding the ViewController class for entering information of the master products

Defining protocol, outlets, and action methods in the header file

Designing the View of the MasterProductController class and connecting controls

Invoking the delegate and ImagePicker methods from the implementation file

Module to create a menu for manipulating the MasterProduct information

Adding the View Controller class to display a menu for adding, editing, and displaying the MasterProducts

Defining the outlets and action methods in the header file

Designing the View of the MasterProductInfoController class and connecting controls

Coding in the implementation file to save, edit, and display the master product's information

Summary

10. Editing the Stock Information

Module to connect the MasterProduct's menu to the rest of the project

Defining outlets and action methods in the header file

Adding a Toolbar and a Bar Button Item in the RootViewController class

Coding in the implementation file to invoke the View of the MasterProductinfoController class

Making the Toolbar to appear at the bottom of the View

Running the application

Selecting the image of the master product

Deleting the master product

Module to modify the information of the master product

Adding the View Controller class to display the view to modify the selected master product

Defining the outlets and action methods in the header file

Designing the View of EditMasterProductController class

Coding in the implementation file to modify the master product's information

Importing the delegate and the View Controller class in the header file

Coding in the implementation file to invoke the View of the EditMasterProductController class

Summary

11. Displaying the Products for Sale and Updating the Stock

Displaying the products available for sale

Adding the SearchProductController class

Designing the view of SearchProductController

Coding in the SearchProductController class

Invoking the SearchProductController from the Product menu

Displaying name, price, and image of the selected product

Updating the stock

Running the project

Automatically updating the quantity of the product in the MasterProduct entity

Versioning

Creating a new Data Model version

Migrations

Implementing lightweight migration to our application

Summary

A. Appendix

Index

Core Data iOS Essentials

Core Data iOS Essentials

Copyright © 2011 Packt Publishing

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First published: April 2011

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Published by Packt Publishing Ltd. 32 Lincoln Road Olton Birmingham, B27 6PA, UK.

ISBN 978-1-849690-94-2

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Cover Image by Asher ( <[email protected]> )

Credits

Author

B.M. Harwani

Reviewers

Fred McCann

Muhammad Adil

Acquisition Editor

David Barnes

Development Editor

Chris Rodrigues

Technical Editor

Aditi Suvarna

Copy Editor

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Indexer

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Cover Work

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About the Author

B.M. Harwani is the founder and owner of Microchip Computer Education (MCE), based in Ajmer, India that provides computer education in all programming and web developing platforms. He graduated with a B.E. in computer engineering from the University of Pune, and also has a 'C' Level (Master's diploma in computer technology) from DOEACC, Government Of India. Having been involved in the teaching field for over 16 years, he has developed the art of explaining even the most complicated topics in a straightforward and easily understandable fashion. He has written several books on various subjects that include JSP, JSF, EJB, PHP, .NET, Joomla, jQuery, and Smartphones. He also writes articles on a variety of computer subjects, which can be seen on a number of websites. To know more, visit his blog, http://bmharwani.com/blog.

The list of books written by B.M. Harwani are Programming & Problem Solving through C (BPB, 2004), Learn Tally in Just Three Weeks (Pragya, 2005), Data Structures and Algorithms through C (CBC, 2006), Master Unix Shell Programming (CBC, 2006), Business Systems (CBC, 2006), Practical Java Projects (Shroff, 2007), Practical Web Services (Shroff, 2007), Java for Professionals (Shroff, 2008), C++ for Beginners (Shroff, 2009), Practical ASP.NET 3.5 Projects (Shroff, 2009), Java Server Faces—A Practical Approach for Beginners (PHI Learning, 2009), Practical JSF Project using NetBeans (PHI Learning, 2009), Foundation Joomla (Friends of ED, 2009), Practical EJB Projects (Shroff, 2009), Data Structures and Algorithms in C++ (Dreamtech Press, 2010), Developing Web Applications in PHP and AJAX (Tata McGraw Hill, 2010), and jQuery Recipes (Apress, 2010).

Acknowledgement

I owe a debt of gratitude to David Barnes, the Senior Acquisition Editor at Packt Publishing for his initial acceptance and giving me an opportunity to create this work. I am highly grateful to the whole team at Packt Publishing for their constant cooperation and contribution to create this book.

My gratitude to Chris Rodrigues, who as a Development Editor offered a significant amount of feedback that helped to improve the chapters. He played a vital role in improving the structure and the quality of information.

I must thank Muhammad Adil, the Technical Reviewer for his excellent, detailed reviewing of the work and the many helpful comments and suggestions he made.

Special thanks to Aditi Suvarna, the Technical Editor for first class structural and language editing. I appreciate her efforts in enhancing the contents of the book and giving it a polished look.

I also thank Alwin Roy, the Production Coordinator for doing excellent formatting and making the book dramatically better.

A big and ongoing thanks to Vishal Bodwani, the Project Coordinator for doing a great job and sincere efforts by the whole team to get the book published on time.

A great big thank you to the editorial and production staff and the entire team at Packt, who worked tirelessly to produce this book. I really enjoyed working with each one of you.

I am also thankful to my family—my small world; Anushka (my wife) and my two little darlings, Chirag and Naman for allowing me to work on the book even during the time that I was supposed to spend with them.

I should not forget to thank my dear students who have been a good teacher for me as they make me understand what basic problems they do face in a subject and enable me to directly hit at those topics. It is because of the endless interesting queries of my students that help me in writing the books with a practical approach.

About the Reviewers

Fred McCann is a co-founder of Zumisoft, an independent Mac software company. He started writing code at the tender age of eight on a TI-99a home computer and has since moved on to newer systems. His interests, outside of programming, include Judo, Yoga, Hiking, Kites, Amateur Robotics, Politics, and Meditation.

His websites include http://www.duckrowing.com/ and http://www.fredmccann.com/Home.html.

Muhammad Adil graduated from the National University of Computer and Emerging Sciences in Pakistan, with a Bachelor's degree in Computer Science. He was a very active Freelance Software developer during his university years. So, after graduating, he kept working as a Freelance developer and has been working as an iOS developer for the past one and a half years.

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This book is dedicated to my mother Mrs. Nita Harwani and Mark Zuckerberg.

My mother is next to God for me and whatever I am today is because of the moral values taught by her.

It is because of Mark Zuckerberg's amazing development; Facebook that I could meet my school and Engineering college friends after a long break of 18 years.

Preface

Since its invention, iPhone has been inspiring developers around the world to develop applications for it. Several applications can be built for iPhone, which include Web applications, Native iPhone applications, Games, Weather, News applications, Data driven applications, and so on.

Looking at the huge demand of developing data applications for iPhone inspired me to write a book on Core Data—a perfect framework for developing data-driven applications for iPhone. In this book, I have tried my level best to keep the code simple and easy to understand. I have provided step-wise instructions with screenshots at each step. Feel free to contact me at <[email protected]> for any queries. Any suggestions for improving the book will be highly appreciated.

What this book covers

In Chapter 1, Overview, you will see a brief history of the Core Data and a small introduction to EOF and Xcode.

In Chapter 2, Understanding Core Data, you will have an introduction to the Core Data framework and its features. You will learn about the data model and how it defines the structure of data in terms of entities, properties, and their relationships. Also, you will get a brief idea of Model View Controller (MVC), the Core Data API and its main components. Besides this, the chapter includes an overview of the application (Sales Record System for a Store), which we will be building in the book along with its different views and the tasks performed when different controls in these views are selected.

Chapter 3, Understanding Objective-C Protocol and Table View, explains how an object collaborates with other objects through the delegation pattern. We will learn about the working of a protocol, that is, how a protocol and its methods are defined. We will also learn how an object adopts a protocol to act as a delegate and how a protocol establishes a contract for communication between two objects.

Chapter 4, Designing a Data Model and Building Data Objects for Customers, introduces the working of UITableView and explains step-by-step how information is displayed via the table view. The chapter explains the different methods used in displaying information through table view and also how to add more information to the existing information being displayed via table view. For instance, if four names are already being displayed in a table, this chapter will show how to add the newly entered name to the existing list of names in the table.

In Chapter 5, Creating, Listing, and Deleting Names of Customers, we will be learning how to design a data model for storing any customer's information, that is, we will define the Customer entity and its attributes. Also, we will learn to build the data object (classes) associated with the Customer entity.

Chapter 6, Creating, Listing, Displaying, and Deleting Records of Customers, focuses on explaining how a customer's information, which is stored in the Customer entity, is maintained. The chapter gives a step-by-step explanation of how to save, display, and delete the customer information that comprises customer's name, e-mail address, and contact number.

In Chapter 7, Updating and Searching Records of Customers, we will see how to modify the customer information, which is, unlike the "editing" feature in Chapter 6 that was limited to the deletion of a record; we will see how to update (modify) the information of the existing customers. The chapter explains the procedure to add an Edit button to the view, which when selected will allow us to edit the information of the selected customer. This chapter also covers how to save the modified information back to the persistent store. In this chapter, we will also learn the application of NSPredicate to apply query facility to locate the desired customer quickly.

Chapter 8, Entering, Saving, Listing, and Deleting the Records of the Products Sold to the Customers, explains how to store the information of the products purchased by different customers, we will learn to add the Product entity to our existing data model and we will see how the relationship is established from the Customer entity to the Product entity. The chapter also explains how the inverse relationship is set from the Product entity to the Customer entity and finally, the procedure of building data objects for the modified data model. Also, we will learn how to maintain the product's information, that is, how to enter, save, display, and edit the information of the products that are sold to different customers. We will learn how to develop a view to enter the product's information, develop a product's menu to add, edit, and display the products sold to the selected customer and finally, to connect the product's menu to the rest of the application.

Chapter 9, Entering, Displaying, and Deleting the Stock, covers the creation of a Master Product entity, which will be used for storing the information of products that the vendor is dealing with. All the products available for sale are stored in this table. In order to store the image of the product, the chapter explains the concept of transformable data type that is used for creating custom data types. The chapter also explains how to enter, save, display, delete, and modify the information of the master products that the vendor deals with. It also covers the working of the Image Picker control—how it is used in selecting images of the products and the different methods to define the size of the image of the product. In all, the chapter explains how to develop a view to enter master product's information, develop a menu to add, delete, and display information of master products for the MasterProduct.

Note

The information of the products entered in the MasterProduct entity is very different from the information of the product entered in the Product entity. The Product entity stores the information of the products that are sold to the customers, whereas the MasterProduct entity refers to the products that are available for sale.

Chapter 10, Editing the Stock Information, explains how to connect the menu meant for adding, deleting, and displaying the Master Product information to the rest of the application. Also, the chapter covers the step-by-step approach to develop a view to display and modify the selected master product's information.

In Chapter 11, Displaying the Products for Sale and Updating the Stock, we will learn how to implement query facility while entering the information of the products sold to the selected customer. Also, we will see how the quantity of the master product gets automatically reduced by the amount of quantity sold to the selected customer.

Appendix, Appendix, will give you a brief idea about the topics covered in this book.

What you need for this book

This book assumes that you have an Intel-based Macintosh running Snow Leopard (Mac OS X 10.6.2 or later). Why Snow Leopard? There are many new features in Xcode that are available only on Snow Leopard. Therefore, I highly recommend upgrading to Snow Leopard, if you are using an earlier release. We will be using Xcode, an integrated development environment used for creating applications for iPad, iPhone, core data, and other Mac applications. So, download the latest version of Xcode from the following link: http://developer.apple.com/technologies/xcode.html.

The latest version of Xcode that is available at the time of this writing is Xcode 3.2.5. I have used the same version for developing the core data application in this book.

Who this book is for

This book is mainly written for those who are familiar with iPhone SDK programming and are interested in developing data-driven applications using Core Data. For understanding the concept of Core Data better, knowledge of Objective C protocol and delegation pattern is required. Besides this, familiarity with the data source patterns, such as UITableView and UITableViewDataSource, for the purpose of displaying information is also required. But never mind if you are not aware of these two concepts, Chapters 3 and 4 of the book are focused on getting you acquainted with them.

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Chapter 1. Overview

This book is a practical guide to help you in developing Data-Driven iPhone applications using Core Data. The tremendous success of iPhone has increased the demand of mobile applications. Besides the Game-based applications, there is a huge market for the data-driven mobile applications too. The focus of this book is to make you understand how the Core Data, Apple's persistence framework, is used for developing data-driven mobile applications.

Prerequisite

This book assumes that you have a basic understanding of the iPhone SDK and you also know the basics of iPhone SDK programming.

To better understand the concept of Core Data, you should:

Have a good understanding of the Objective-C protocol and the delegation patternBe familiar with data source patterns, such as UITableView and UITableViewDataSource, for the purpose of displaying information

Even if you're not aware of these two concepts, Chapter 3, Understanding Objective-C Protocol and Table View and Chapter 4, Designing a Data Model and Building Data Objects for Customers of the book are focused to get you acquainted with them. That is why the two chapters are self-contained and each chapter presents an individual application.

A brief history

The iPhone as we all know is an integrated cellular telephone and media player developed and marketed by Apple. It has become very popular in the past few years because of its amazing features. Looking at its huge number of users, developers around the world are attracted to develop applications for this unique device. Developers realized that besides games, there is a huge market of data applications for iPhone device. The attraction of creating data applications for iPhone device resulted into development of the Core Data framework. But the question is where did Core Data come from?

Core Data was first developed at NeXT Computer as the DBKit framework in 1992, which then became the Enterprise Object Framework (EOF) in 1994.

Enterprise Object Framework (EOF)

EOF is an object-relational mapping (ORM) framework that provides a mechanism for accessing the data as an object-oriented class structure. It is well-designed and encourages Model View Controller (MVC) design patterns. It also simplifies the tedious job of creating an application's data model. EOF is not just a framework, it is also a tool that helps in creating the application's data model visually—the task that was previously done by creating Objective-C classes. Besides this, the framework handles all the work involved in persisting the data to a SQL database, flat file, or any other data store. Based on object-oriented architecture, EOF is very flexible to use too. The roots of the Core Data framework come from the Enterprise Objects Framework (EOF).

Core Data

Core Data is part of the Cocoa API in Mac OS X first introduced with Mac OS X 10.4 Tiger and for the iOS with iPhone SDK 3.0. It is a powerful data model framework that was specifically designed to provide local data storage for Cocoa applications. The modeling functionality of Core Data is integrated right into XCode, so there's no need to switch back and forth between the IDE and modeler. With interface builder, it allows developers to quickly create a user interface (known as the views of the application in MVC terminology) without writing a single line of code. It is also the most effective solution to data persistence and allows us to persist our data to any number of different storage mediums, which includes storing data as XML, in binary files, or in an embedded SQLite database. The data modeling tool of Xcode allows us to define our application's data model graphically, which can be easily accessed through code. Instances of the entities defined in the data model are then managed by the Core Data framework and stored to a storage medium such as an XML file or SQLite database.

Now the question arises, what is Xcode and why we are using it for developing Core Data applications?

Why use Xcode?

Xcode is Apple's most comprehensive Software Development Kit (SDK), and it provides an environment for developing the applications for iPhone. It is a highly customizable integrated development environment (IDE) that includes compilers and applications, together with an extensive set of programming libraries and interfaces. It is a powerful source editor and a graphic debugger too. While developing applications with XCode, it gives us an option to enable a checkbox for enabling Core Data support. On selecting the checkbox, Xcode automatically creates code for us that make the task of developing core data applications quite easy.

Source code

The source code of the book is available at the URL specified in the Preface of the book.

You'll find chapter-wise code bundle in the ZIP file. The book is so organized that it guides you to develop a data-drive application step-by-step. That is, by the end of the book, you'll be having a complete data-driven running application with you. In case, you want to run the end product directly, follow the below given steps:

Unzip the source bundle of the last chapter, Chapter 11, Displaying the Products for Sale and Updating the Stock on your local Mac. Open Xcode, go to File | Open from the menu, and browse to the unzipped bundle of Chapter 11, Displaying the Products for Sale and Updating the Stock. In the prob folder, select the prob.xcodeproj file followed by clicking on the Open button. Select the Build and Run icon from the Xcode project window to run the application. You'll get the main view of the application as shown in the following image. But the application is not yet ready to run until we define the photos of the master products (products that we are going to sell through application). To define photos of the master products in iPhone Simulator, go to Home and then click on the Photos icon (refer to the given image (a)). We get the Albums page as shown in image (b). Because we have not created any photo album yet, the figure displays the message, No Photos. Drag the first image, IMG_0000.JPG provided in the code bundle of Chapter 11, Displaying the Products for Sale and Updating the Stock onto the simulator screen. Tap on the image and hold down the mouse on the image until the popover comes up, as shown in image (c). Click on the Save Image button to save the image. Repeat the procedure for the other three images (IMG_0001.JPG, IMG_0002.JPG, IMG_0003.JPG). After saving the four images, the simulator will display the images as shown in image (a). On clicking back to Photos, we find that an album Saved Photos appears with one of the images considered as the icon of the photo album (image (b)). The number (4) in parenthesis represents that there are four images in this photo album. Now, our application is completely ready for execution. For any guidance regarding operating the application, refer to the An application output sample section in Chapter 2,

Shall we begin?

After following how our book will proceed, let us now get ready to dive in. Get ready for the introduction of Core Data and the step-by-step journey to understand its different concepts and applying them practically in developing a data-driven mobile application.

Chapter 2. Understanding Core Data

In this book, we'll learn how to build a Sales Record Keeping System application using Core Data through a step-by-step approach. So, this chapter will give us an introduction to the following topics:

Core Data framework and its featuresThe data model and how it defines the structure of data in terms of entities, properties, and their relationshipsModel-View-Controller (MVC)Core Data API and its main componentsAn overview of the application that we will be building in this book and a glance at the different application views and the tasks performed when different controls in these views are selected

Core Data

Core Data is Apple's persistence framework, which is used to persist—store our application's data in a persistent store, which may be memory or a flat file database. It helps us represent our data model in terms of an object graph, establish relationships among objects, and it can also store object graphs on the disk. It also allows us to use the entities of our data model in the form of objects, that is, it maps our data into a form that can be easily stored in a database, such as SQLite, or into a flat file. Also, the Core Data reduces a lot of coding. On using Xcode's templates for Core Data applications, we automatically get the boilerplate code that does several complex tasks such as generating XML files, binary files, SQLite files automatically for us without writing a single code, allowing us to focus on the business logic of our application.

Besides this, Core Data also provides several features that are required in data manipulation, which includes filtering data, querying data, sorting data, establishing relationships with other data, and persisting data in different repositories.

Core Data features

The Core Data framework provides lots of features that include the following:

Supports migrating and versioning: It means we can modify our data model, that is, entities of the application, whenever desired. The Core Data will replace the older persistent store with the revised data model. This concept is nicely explained with figures in Chapter 11,Supports Key-Value Coding (KVC): It is used to store and retrieve data from the managed objects. Core Data provides the methods required for setting and retrieving attribute values from the managed object, respectively. We will be using this feature in our application to display the information of customers and the products sold to them through the table view.Tracks the modifications: Core Data keeps track of the modifications performed on managed objects thus allowing us to undo any changes if required. We will be using this feature in our application while modifying the information of a customer or product to know what the earlier value was and what the new value entered for it is.Supports lazy loading: It's a situation that arises when all the property values of a managed object are not loaded from the data store and the property values are accessed by the application. In such situations, faulting occurs and the data is retrieved from the store automatically.Efficient database retrievals: Core Data queries are optimized for this, though the execution of query is dependent on the data store.Multi-threading: Core Data supports multi-threading in an application, that is, more than one thread can be executed in parallel to increase performance. Even some tasks can be performed in the background using a separate thread.Inverse relationship: Core Data maintains an inverse relationship for consistency. If we add an object to a relationship, Core Data will automatically take care of adding the correct object to the inverse relationship. Also, if we remove an object from a relationship, Core Data will automatically remove it from the inverse relationship. In our application, we will be using an inverse relationship between the Customer and Product entities, so that if a customer is deleted, the information of all the products purchased by him/her should also be automatically deleted.External data repositories: Core Data supports storing objects in external data repositories in different formats.

Data Model

Core Data describes the data in terms of a data model. A data model is used to define the structure of the data in terms of entities, properties, and their relationships.

Entities

Because Core Data maintains data in terms of objects, an entity is an individual data object to represent complete information of the person, item, object, and so on. For example, customer is an entity, which represents information of customers, such as name, address, e-mail ID, contact number, products purchased, date of purchase, and so on. Similarly, the product is an entity, which represents the information of a product, such as name of the product, price, weight, and so on. An entity consists of properties that are a combination of attributes and relationships. An entity in Xcode's Data Model Editor may appear as shown in the following screenshot:

Properties

Properties of an entity give detailed information about it, such as what are its attributes and how it is related to other entities. A property of an entity refers to its attributes and relationships. Attributes are scalar values and relationships are pointers to or collections of other entities at the object level. A property is represented by a name and a type.

Attributes

Attributes are the variables within an object (entity). In fact, a collection of attributes makes an entity. In database language, they are known as columns of the table. For example, the customer's entity may consist of attributes such as name, address, contact number, items purchased, and so on. Similarly, the attributes in the products table may be item code, item name, quantity, and so on. While creating attributes of an entity, we have to specify its name and its data type to declare the kind of information (whether integer, float, string, and so on) that will be stored in the attribute. Also, we can define the constraints on the information that can be stored in the column. For example, we can specify the maximum, minimum value (range) that can be stored in that attribute, or whether the attribute can or cannot store certain special symbols, and so on. Also, we can specify the default value of an attribute.

Relationships

Besides attributes, an entity may also contain relationships (which define how an entity is related to other entities). The attributes and relationships of an entity are collectively known as properties. The relationships are of many types (To-One, To-Many, and Many-to-Many) and play a major role in defining connection among the entities and what will be the impact of insertion or deletion of a row in one entity on the connected entities.

Examples of relationship types:

The relationship from a child entity to a parent entity is a To-One relationship as a child can have only one parentThe relationship from a customer to a product entity is a To-Many relationship as a customer can purchase several productsThe relationship from an employee to a project entity is of Many-to-Many type as several employees can work on one project and an employee can work on several projects simultaneously

Note

To define a many-to-many relationship in Core Data, we have to use two To-many relationships. The first To-many relationship is set from the first entity to the second entity. The second To-many relationship is set from the second entity to the first entity.

In Xcode's Data Model Editor, the relationship from Customer to Product—a To-Many relationship—is represented by a line that appears pointing from the Customer entity to the Product entity with two arrows, (designating a One-to-Many relationship) as shown in the subsequent screenshot, whereas the To-One relationship is represented by a line with a single arrow:

When defining relationships in Core Data we may use inverse relationships, though it's optional.

Inverse relationship

In Core Data, every relationship can have an inverse relationship. Like, if there is a relationship from Customer to Product, there will be a relationship from Product to Customer too. A relationship does not need to be the same kind as its inverse; for example, a To-One relationship can have an inverse relationship of type To-Many. Although relationships are not required to have an inverse, Apple generally recommends that you always create and specify the inverse, (even if you won't need) as it helps Core Data to ensure data integrity.

For example, consider a situation when a Customer entity has a relationship of the To-Many type to a Product entity and some information of a customer is changed or a row of a customer is deleted. Then it will be easier for Core Data to ensure consistency; that is, by inverse relationship, Core Data can automatically find the products related to the deleted customer and hence, delete them too. Inverse relationship is practically used in Chapter 8, Entering, Saving, Listing, and Deleting the Records of the Products Sold to the Customers.

Before we go further, let us have a quick look at the architecture that is used in iPhone application development: MVC.

Model View Controller (MVC)

iPhone application development uses MVC architecture where M stands for Model, V stands for View, and C for Controller.

Model