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Android Kotlin app showcasing Data Persistence with the Android Room Library

Course Outline Learning Outcomes:

Installing Data Persistence in your App with the Android Room Library

Introduction to Room

Adding Room to a Project

Creating database, Entities, DAOs

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You have had some training in Relational Databases and SQL.

In Android OS: there is a SQLite database built into the OS.

Step-by-step lab instruction book to build an Android Kotlin app showcasing Data Persistence with the Android Room Library.

Finished Working Version of this APP Coding:

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https://www.dropbox.com/scl/fi/jgkz1qlpwee69boocd0uh/BookLibraryApp.zip?rlkey=x6qwxfzqk6ue9djzwapr3uvva&dl=0⁠

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This lab will cover the basics of Room, including:

Setting up the project,

creating entities,

DAOs Data Access Objects, and

demonstrating simple CRUD operations (using ROOM Annotations).

We'll also include displaying and updating an image using an ImageView.

See also: Understanding Annotations in Programming:

https://coda.io/@peter-sigurdson/lecture-understanding-annotations-in-programming⁠

Here's a comprehensive catalog of programming elements that go into making the Android Room Database Library work:

1. Annotations:

- @Entity: Marks a class as a database table

- @PrimaryKey: Designates the primary key of an entity

- @ColumnInfo: Specifies the name of a column in the table

- @Ignore: Excludes a field from being persisted to the database

- @Embedded: Allows you to nest objects within entities

- @Relation: Defines relationships between entities

- @ForeignKey: Specifies a foreign key constraint

- @Index: Creates an index on one or more columns

- @Database: Marks a class as a Room database

- @Dao: Identifies a Data Access Object interface

- @Query: Specifies an SQL query

- @Insert: Marks a method for inserting data

- @Update: Marks a method for updating data

- @Delete: Marks a method for deleting data

- @Transaction: Ensures that a set of operations is performed atomically

2. Classes and Interfaces: - RoomDatabase: Abstract base class for database instances - Entity classes: Kotlin data classes representing database tables - DAO data access object interfaces: Define database operations - TypeConverter: Converts complex types to and from database-storable values - Migration: Handles database schema changes

3. Room Database Builder: - Room.databaseBuilder(): Creates a RoomDatabase instance

4. Query Methods: - @Query annotated methods in DAOs - Support for complex queries, including JOINs and subqueries

5. Asynchronous Operations: - Coroutines support: suspend functions in DAOs - Flow return types for observing database changes - RxJava support

6. Transactions: - @Transaction annotation for atomic operations - runInTransaction() method for custom transactions

7. Type Converters: - @TypeConverter annotation - Custom type converter methods

8. Database Views: - @DatabaseView annotation for creating database views

9. Full-Text Search: - FTS3 and FTS4 support using the @Fts3 or @Fts4 annotations

10. Database Inspector: - Built-in tool in Android Studio for inspecting Room databases

11. Testing: - Room.inMemoryDatabaseBuilder() for creating in-memory databases for testing

12. Migrations: - Migration class for defining database migrations - addMigrations() method in database builder

13. Indices: - @Index annotation for creating database indices

14. Callbacks: - RoomDatabase.Callback for database creation and opening callbacks

15. Prepackaged Databases: - createFromAsset() and createFromFile() methods for including pre-populated databases

16. Multi-threading: - Dispatchers for executing database operations on background threads

17. Kotlin Extensions: - KTX extensions for more idiomatic Kotlin code with Room

18. Paging: - Integration with the Paging library for efficiently loading and displaying large data sets

19. Database Export Schema: - exportSchema property in @Database annotation for generating schema files

20. Compile-time Checking: - Room's annotation processor for validating SQL queries at compile-time

21. Lazy Loading: - Lazy relationships using @Relation with lazy = true

22. Auto-generation of Primary Keys: - autoGenerate property in @PrimaryKey annotation

23. Query Parameters: - Named parameters in @Query methods

24. Reactive Streams: - Publisher return types for RxJava integration

25. Incremental Annotation Processing: - Support for faster builds with incremental annotation processing

This catalog covers the main programming elements used in the Android Room Database Library. Each of these elements plays a crucial role in making Room a powerful and flexible ORM solution for Android app development. Understanding and effectively using these components will allow you to create efficient, robust, and maintainable database operations in your Android applications.

Is Android Room Database Library a wrapper about the sqlite database in Android OS?

Can I write SQL directly?

Yes, and Yes.

Android Room as a wrapper for SQLite:

The Android Room Database Library is indeed a wrapper around the SQLite database that comes built into the Android operating system.

Room provides an abstraction layer that sits on top of SQLite, offering several advantages:

It simplifies database operations by providing an object-oriented interface.

It reduces boilerplate code typically associated with direct SQLite usage.

It provides compile-time verification of SQL queries.

It offers seamless integration with other Android Jetpack components.

However, under the hood, Room is still using SQLite for actual data storage and retrieval.

Writing SQL directly:

Yes, you can write SQL directly when using Room. In fact, Room encourages you to write SQL for more complex queries. This is done using the @Query annotation in your Data Access Objects (DAOs).

Here's an example:

@Dao

interface BookDao {

@Query("SELECT * FROM books WHERE author = :authorName")

fun getBooksByAuthor(authorName: String): List<Book>

@Query("SELECT * FROM books WHERE price > :minPrice ORDER BY price DESC")

fun getExpensiveBooks(minPrice: Double): List<Book>

}

In these examples, you're writing raw SQL queries. Room will verify these queries at compile-time to catch any SQL syntax errors early.

Moreover, Room allows you to use more complex SQL features like:

JOINs

Subqueries

Complex WHERE clauses

Aggregate functions (SUM, AVG, COUNT, etc.)

GROUP BY and HAVING clauses

For example:

@Query("""

SELECT authors.name, COUNT(books.id) as bookCount

FROM authors

LEFT JOIN books ON authors.id = books.authorId

GROUP BY authors.id

HAVING bookCount > 0

ORDER BY bookCount DESC

""")

fun getAuthorsWithBookCounts(): List<AuthorBookCount>

This query demonstrates a JOIN, COUNT, GROUP BY, HAVING, and ORDER BY clause all in one complex SQL statement.

While Room provides convenience annotations like @Insert, @Update, and @Delete for simple operations, the ability to write custom SQL queries gives you the flexibility to perform complex database operations when needed.

It's worth noting that while you can write SQL directly, Room still provides type safety and automatic mapping between your SQL queries and Kotlin objects, which is a significant advantage over using raw SQLite.

Lab Part A:

Theory lecture explaining the operation of the Android Room Library and Data Access Objects (DAOs) in the context of the Android App Architecture:

Lecture: Android Room Library and Data Access Objects in Android App Architecture

1. Introduction to Android App Architecture

The Android app architecture is a set of guidelines and best practices for designing robust, testable, and maintainable Android applications. It typically consists of several layers:

- Presentation Layer: UI components (Activities, Fragments) and ViewModels - Domain Layer: Use cases and business logic - Data Layer: Repositories and data sources (local database, network, etc.)

Room fits into the Data Layer of this architecture, providing a powerful abstraction for local data persistence.

What are coroutines in the Android Kotlin App:

Coroutines in an Android Kotlin app are a concurrency design pattern that simplifies asynchronous programming. They enable you to write cleaner and more readable code for managing long-running tasks such as network requests or database operations without blocking the main thread, thereby keeping the app responsive.

Added to Kotlin in version 1.3, coroutines help by converting asynchronous callbacks into a sequential code form. This not only reduces the complexity of callback-based code but also supports features like lightweight threading, built-in cancellation, and structured concurrency.

By integrating coroutines, you can perform tasks asynchronously while avoiding issues like memory leaks and blocking the main application thread, which can lead to unresponsiveness or application crashes. Additionally, many Jetpack libraries provide extensions that offer full coroutine support, making it seamless to integrate coroutines within the Android architecture.

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https://developer.android.com/kotlin/coroutines⁠

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https://developer.android.com/kotlin/coroutines/coroutines-adv⁠

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https://developer.android.com/codelabs/kotlin-coroutines⁠

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https://kotlinlang.org/docs/coroutines-overview.html⁠

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2. Overview of Android Room Library

Room is an SQLite object mapping library that's part of Android Jetpack.

Introduction to Android Jetpack: Android Jetpack is a suite of libraries, tools, and guidance developed by Google to help developers create high-quality Android applications more easily.

Launched in 2018, Jetpack components are designed to work together while taking advantage of Kotlin language features to improve productivity.

Key Aspects of Android Jetpack:

1. Purpose: - Accelerate Android app development - Reduce boilerplate code - Solve common Android problems - Provide best practices and compatibility

2. Components: Jetpack is composed of several components categorized into four main areas:

a) Foundation: - AppCompat: Provides backward compatibility for newer Android features - Android KTX: Kotlin extensions for more concise, idiomatic Kotlin code - Multidex: Enables apps to exceed the 64K method limit - Test: Testing tools and APIs for unit and runtime UI tests

b) Architecture: - Data Binding: Declaratively bind UI components to data sources - Lifecycles: Manage activity and fragment lifecycles - LiveData: Observable data holder class - Navigation: Handle in-app navigation - Room: SQLite database abstraction layer - ViewModel: Store and manage UI-related data - WorkManager: Manage background jobs

c) Behavior: - Download Manager: Schedule and manage large downloads - Media & Playback: Consistent media controls across devices - Notifications: Create and manage notifications - Permissions: Tools for checking and requesting permissions - Sharing: Share content between apps - Slices: Create flexible UI elements that can display app data outside the app

d) UI: - Animation & Transitions: Move widgets and transition between screens - Auto, TV, and Wear OS: Build apps for different device types - Emoji: Enable updated emoji fonts on older platforms - Fragment: A basic unit of composable UI - Layout: Lay out widgets using different algorithms - Palette: Extract color palettes from images

3. Benefits: - Modular: Use only what you need - Backwards compatible: Works on a wide range of Android versions - Tested: Reduces bugs and simplifies testing - Integrated: Components are designed to work together seamlessly

4. Architecture Guidelines: Jetpack promotes the MVVM (Model-View-ViewModel) architecture pattern, which separates the UI from the business logic, making apps easier to test and maintain.

5. Kotlin-first: While Jetpack works with both Java and Kotlin, it's designed to take advantage of Kotlin's language features for more concise and expressive code.

6. Continuous Updates: Jetpack components are updated regularly, independent of Android platform releases, allowing developers to access new features and improvements more frequently.

7. Community and Support: Jetpack is widely adopted in the Android development community and has extensive documentation, codelabs, and samples provided by Google.

In conclusion, Android Jetpack is a comprehensive set of libraries and tools that significantly simplifies Android app development. By providing solutions to common challenges and promoting best practices, Jetpack allows developers to focus on creating unique features for their apps rather than reinventing the wheel for standard functionalities. As you progress in your Android development journey, becoming familiar with Jetpack components will be crucial for building modern, robust, and efficient Android applications.

Android Room Library povides an abstraction layer over SQLite, allowing for more robust database access while harnessing the full power of SQLite.

Key components of Room:

a) Database: Represents the database and serves as the main access point for the underlying connection.

b) Entity: Represents a table within the database.

c) DAO (Data Access Object): Contains methods for accessing the database.

3. Entities in Room

Entities are annotated Kotlin data classes that represent tables in your database.

Example: ```kotlin @Entity(tableName = "books") data class Book( @PrimaryKey val id: Int, @ColumnInfo(name = "title") val title: String, @ColumnInfo(name = "author") val author: String ) ```

- The `@Entity` annotation defines a table. - `@PrimaryKey` marks the primary key of the table. - `@ColumnInfo` allows you to customize column names.

4. Data Access Objects (DAOs)

DAOs are interfaces or abstract classes annotated with `@Dao`.

They define the methods for accessing the database. Corresponding to SQL CRUD Operations.

Example: ```kotlin @Dao interface BookDao { @Query("SELECT * FROM books") fun getAllBooks(): List<Book>

@Insert fun insertBook(book: Book)

@Delete fun deleteBook(book: Book) } ```

- `@Query` is used for custom SQL queries. - `@Insert`, `@Delete`, `@Update` are convenience annotations for common operations.

5. Room Database

The Room Database is an abstract class that extends RoomDatabase.

It serves as the main access point for the underlying SQLite database connection.

Example: ```kotlin @Database(entities = [Book::class], version = 1) abstract class AppDatabase : RoomDatabase() { abstract fun bookDao(): BookDao

companion object { private var instance: AppDatabase? = null

fun getInstance(context: Context): AppDatabase { if (instance == null) { instance = Room.databaseBuilder( context.applicationContext, AppDatabase::class.java, "app_database" ).build() } return instance!! } } } ```

6. Room in the Context of Android App Architecture

Design Patterns:

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In the Android app architecture, Room operates within the Data Layer:

a) Repository Pattern: Room is often used in conjunction with the Repository pattern.

The Repository acts as a single source of truth for data, mediating between different data sources (like Room for local storage and Retrofit for network requests).

b) ViewModel Integration: ViewModels in the Presentation Layer can use repositories to access data from Room, keeping the UI updated with the latest data.

c) Coroutines and Flow: Room supports Kotlin coroutines and Flow, allowing for efficient asynchronous database operations and reactive UI updates.

7. Benefits of Using Room

- Compile-time verification of SQL queries - Convenience annotations that minimize boilerplate code - Seamless integration with other Android Jetpack components - Built-in migration support - Testability: Room allows you to easily test your database and queries

8. Best Practices

- Use abstraction: Don't expose Room DAOs directly to the UI. Instead, use repositories.

- Perform database operations on background threads (using coroutines or RxJava).

- Use type converters for complex data types.

- Implement proper indexing for better query performance.

- Use Room's migration support for handling database schema changes.

Conclusion:

Room simplifies database operations in Android, providing a powerful abstraction over SQLite.

By using entities to represent database tables,

DAOs to define database operations,

and the Room database as the main access point (single source of Truth for your Data),

developers can create efficient, type-safe database interactions.

When integrated properly into the Android app architecture, Room contributes to creating more maintainable and testable applications.

Look for ways to push as much of the Algorithm Processing as possible into your Data Store, and use SQL as much as possible rather than reinventing the wheel.

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