Mark L. Murphy - Elements of Android Room Version 0.6

Headings formatted in bold-italic have changed since the last version.

Thanks!

Thanks for your interest in Room! Room is Googles solution for a high-level databaseaccess API, for your local SQLite databases. As such, Room gets a lot of attentionand is reasonably popular.

Thanks also for your broader interest in Android app development! Android is the most widely-usedoperating system on the planet, so we need to be able to rapidly develop high-qualityAndroid apps. Room can help with that.

And thanks for your interest in this book! Here, you can learn more about how to workwith Room, from the basics through more complex scenarios. And, along the way, theremay be a joke or two.

This book is designed for developers with at least a bit of Android app developmentexperience. If you are fairly new to Android, please consider readingElements of Android Jetpack,Exploring Android, or both, beforecontinuing with this book.

Also note that this books examples are written in Kotlin. If you are unfamiliarwith Kotlin, you can still learn stuff about Room from this book, though it willbe more difficult. You might consider reading Elements of Kotlin,to familiarize yourself with Kotlin.

If you obtained this book through, you will be able to downloadupdates as they become available, for the duration of your subscriptionperiod.

If you obtained this book through other channels um, well, its stilla really nice book!

Each release has notations to show what is new or changed compared with theimmediately preceding release:

• The Table of Contents in the ebook formats (PDF, EPUB, MOBI/Kindle) showssections with changes in bold-italic font
• Those sections have changebars on the right to denote specific paragraphsthat are new or modified

And, there is the Whats New section, just below this paragraph.

This update adds two more chapters, covering:

Also, was updated to Paging 3.

In addition:

• A bunch of dependencies were updated, notably Room itself
• Various bugs were fixed

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The source code in this book is licensed under theApache 2.0 License, in case you have thedesire to reuse any of it.

Copying source code directly from the book, in the PDF editions, works bestwith Adobe Reader, though it may also work with other PDF viewers. Some PDF viewers,for reasons that remain unclear, foul up copying the source code to the clipboardwhen it is selected.

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The author would like to thank Daniel Rivera, Yiit Boyar, and the rest of thedevelopers at Google responsible for Room.

The author would also like to thank Stephen Lombardo, Nick Parker, and the restof Zetetic, plus Nathan Frietas, Hans-Cristoph Steiner, and the rest of the GuardianProject, for all their work on SQLCipher for Android and general Android appsecurity.

Google describes Room as providing an abstraction layer over SQLite to allowfluent database access while harnessing the full power of SQLite.

In other words, Room aims to make your use of SQLite easier, througha lightweight annotation-based implementation of anobject-relational mapping (ORM) engine.

If you have ever worked with a relational database like SQLite froman object-oriented language like Java or Kotlin undoubtedly you have encounteredthe object-relational impedance mismatch.That is a very fancy way of saying its a pain getting stuff intoand out of the database.

In object-oriented programming,we are used to objects holding references to other objects, forming some sortof object graph. However, traditional SQL-style relational databases workoff of tables of primitive data, using foreign keys and join tables toexpress relationships. Figuring out how to get our classes to map torelational tables is aggravating, and it usually results in a lot of boilerplatecode.

Traditional Android development uses SQLiteDatabase for interacting with SQLite.That, in turn, uses Cursor objects to represent the results of queries andContentValues objects to represent data to be inserted or updated. While Cursorand ContentValues are objects, they are fairly generic, much in the way thata HashMap or ArrayList is generic. In particular, neither Cursor norContentValues