CoreData权威指南：iOS 4数据持久化引擎详解

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《Pro Core Data for iOS：iPhone、iPad及iPod touch的数据访问与持久化引擎指南》是一本由Michael Privat和Rob Warner合著的优秀参考书籍，专为iOS 4及后续版本设计。这本书深入讲解了如何在iOS设备上准确而高效地存储和检索应用程序数据。作为Apple的Data Access and Persistence Engine（数据访问与持久化引擎）的权威指南，它提供了全面的技术指导，帮助开发者理解和掌握Core Data框架。本书的核心内容包括但不限于以下几个方面： 1. **入门基础**：为初次接触Core Data的开发者提供基础知识，解释数据模型的设计原则，以及如何在应用程序中创建和管理实体（Entity）、属性（Attribute）和关系（Relationship）。 2. **数据存储与管理**：阐述如何使用NSManagedObject来操作数据，包括创建、读取、更新和删除对象，以及事务处理（Transaction Management）的重要性。 3. **fetch requests**：详细介绍如何使用NSFetchRequest来执行查询，理解高级查询选项，如排序、过滤和分页，以及如何处理结果集。 4. **存储策略**：讨论Core Data的存储策略，包括主键的确定、内存管理、持久化存储的选择（如In Memory、Disk-Based或Cloud-Synchronized）以及备份和恢复机制。 5. **性能优化**：探讨如何提高Core Data性能，比如减少查询次数、使用合适的存储策略、缓存机制和延迟加载（Lazy Loading）。 6. **并发与同步**：讲解在多线程环境下的数据一致性问题，以及如何利用NSManagedObjectContext的并发模式（如Main Queue、Private Queues和Background Queues）来避免竞态条件。 7. **错误处理与调试**：介绍如何识别和解决Core Data运行时错误，以及如何使用Instruments等工具进行性能分析。 8. **高级主题**：涉及更复杂的主题，如链接式存储、元数据、迁移（Migration）和高级查询技巧。《Pro Core Data for iOS》不仅适合专业开发者系统学习Core Data，也是那些希望提升iOS应用数据管理能力的开发者不可或缺的参考资料。版权所有，未经许可，不得擅自复制或传输。通过阅读这本书，开发者可以更好地构建稳定、高效且用户体验优良的iOS应用。

■ACKNOWLEDGMENTS

project, and so many others offered kind words and encouragement. I also thank Geoff Packwood for

helping me rekindle my passion and find my way.

Finally, I thank my parents for the love of learning they instilled in me. They pre-ordered this book

despite their inability to decipher a word of it. They are great people.

—Rob Warner

■INTRODUCTION

Introduction

Once you’ve learned the basics of iOS development and you’re ready to dig deeper into how to write

great iOS applications, Pro Core Data for iOS leads you through the important topic of data persistence.

Storing and retrieving customers’ data is a task you must pull off flawlessly for your application to

survive and be used. Introductory texts give you introductory-level understanding of the Core Data

framework, which is fine for introductory-level applications but not for applications that cross the

chasm from toys to real-life, frequently used applications. This book provides you with the deeper levels

of information and understanding necessary for developing killer apps that store and retrieve data with

the performance, precision, and reliability customers expect and require.

What to Expect from This Book

This book starts by setting a clear foundation for what Core Data is and how it works and then takes you

step-by-step through how to extract the results you need from this powerful framework. You’ll learn

what the components of Core Data are and how they interact, how to design your data model, how to

filter your results, how to tune performance, how to migrate your data across data model versions, and

many other topics around and between these that will separate your apps from the crowd.

This book combines theory and code to teach its subject matter. Although you can take the book to your

Barcalounger and read it cover to cover, you’ll find the book is more effective if you’re in front of a

computer, typing in and understanding the code it explains. We also hope that, after you read the book

and work through its exercises, you’ll keep it handy as a reference, turning to it often for answers and

clarification.

How This Book Is Organized

We’ve tried to arrange the material so that it grows in complexity, at least in a general sense, as the book

progresses. The topics tend to build on each other, so you’ll likely benefit most by working through the

book front to back, rather than skipping around. If you’re looking for guidance on a specific topic—

Chapter

Getting Started

If you misread this book’s title, thought it discussed and deciphered core dumps, and

hope it will help you debug a nasty application crash, you got the wrong book. Get a

debugger, memory tools, and an appointment with the optometrist. Otherwise, you

bought, borrowed, burglarized, or acquired this book somehow because you want to

better understand and implement Core Data in your iOS applications. You got the right

book.

You might read these words from a paper book, stout and sturdy and smelling faintly of

binding glue. You might digitally flip through these pages on a nook, iPad, Kindle, Sony

Reader, Kobo eReader, or some other electronic book reader. You might stare at a

computer screen, whether on laptop, netbook, or monitor, reading a few words at a time

while telling yourself to ignore your Twitter feed rolling CNN-like along the screen’s

edge. Regardless, as you read, you know that not only can you stop at any time but that

you can resume at any time. These words persist on paper and digital page and, with

proper care and timely transformation to future media, can survive your grandchildren’s

grandchildren. Any time you want to read this book, you pick up book, electronic reader,

or keyboard, and if you marked the spot where you were last reading, you can even start

from where you last stopped. We take this for granted with books.

Users take it for granted with applications.

Users expect to find their data each time they launch their applications. Apple’s Core

Data framework helps you ensure that they will. This chapter introduces you to Core

Data, explaining what it is, how it came to be, and how to build simple Core Data---based

applications for iOS. This book walks through the simpleness and complexities of Core

Data. Use the information in the book to create applications that store and retrieve data

r e l i a b l y a n d e ff i c i e n t ly s o t h a t u se r s c a n d e p e n d o n t he i r d at a . C od e c ar e f u l l y , t h o u g h -----

you don’t want to write buggy code and have to deal with nasty application crashes.

What Is Core Data?

When people use computers, they expect to preserve any progress they make toward

completing their tasks. Saving progress, essential to office software, code editors, and

CHAPTER 1: Getting Started

games involving small plumbers, is what programmers call

persistence

. Most software

requires persistence, or the ability to store and retrieve data, to be useful so that users

don’t have to reenter all their data each time they use the applications. Some software

can survive without any data storage or retrieval; calculators, carpenter’s levels, and

apps that make annoying or obscene sounds spring to mind. Most useful applications,

however, preserve some state, whether configuration-oriented data, progress toward

achieving some goal, or mounds of related data that users create and care about.

Understanding how to persist data to iDevices is critical to most useful iOS

development.

Apple’s Core Data provides a versatile persistence framework. Core Data isn’t the only

data storage option, nor is it necessarily the best option in all scenarios, but it fits well

with the rest of the Cocoa Touch development framework and maps well to objects.

Core Data hides most of the complexities of data storage and allows you to focus on

what makes your application fun, unique, or usable.

Although Core Data can store data in a relational database (such as SQLite), it is not a

database engine. It doesn’t even have to use a relational database to store its data.

Though Core Data provides an entity-relationship diagramming tool, it is not a data

modeler. It isn’t a data access layer like Hibernate, though it provides much of the same

object-relational mapping functionality. Instead, Core Data wraps the best of all these

tools into a data management framework that allows you to work with entities,

attributes, and relationships in a way that resembles the object graphs you’re used to

working with in normal object-oriented programming.

Early iPhone programmers didn’t have the power of the Core Data framework to store

and retrieve data. The next section shows you the history behind persistence in iOS.

History of Persistence in iOS

Core Data evolved from a NeXT technology called Enterprise Objects Framework (EOF)

by way of WebObjects, another NeXT technology that still powers parts of Apple’s web

site. It debuted in 2005 as part of Mac OS X 10.4 (‘‘Tiger’’), but didn’t appear on iPhones

until version 3.0 of the SDK, released in June 2009. Before Core Data, iPhone

developers had a few persistence options:

 Use property lists, which contain nested lists of key/value pairs of

various data types.

 Serialize objects to files using the SDK’s NSCoding protocol.

 Take advantage of the iPhone’s support for the relational database

SQLite.

 Persist data to the Internet cloud.

Developers used all these mechanisms for data storage as they built the first wave of

applications that flooded Apple’s App Store. Each one of these storage options remains

viable, and developers continue to employ them as they build newer applications using

newer SDK versions.

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