Android Architecture Component ROOM

Why ROOM Library ?

In android app, We convert raw data into structural data . we use SQLite core library to achieve it .

 It handles CRUD (Create, Read, Update and Delete) operations required for a database. Java classes and interfaces for SQLite are provided by the android.database. SQLite maintains an effective database management system. But this conventional method has its own disadvantages.

• You have to write long repetitive code, which will be time-consuming as well as prone to mistakes.
• Syntax errors in queries
• No compile time error detection (Time consuming)
• Parsing is required to convert data to Plain Old Java Objects (POJO) objects
• It is very difficult to manage SQL queries for a complex relational database.

To overcome this, Google has introduced Room Persistence Library.

What is ROOM? 

Room provides the abstraction layer over the SQLite DB. ROOM is not a database
It has extended features and ease of use over android SQLite library .

Componentes

There are three main components of Room-

• Database: Contains the database holder and serves as the main access point for the underlying connection to your app's persisted, relational data.
  The class that's annotated with @Database should satisfy the following conditions:
  • Be an abstract class that extends RoomDatabase.
  • Include the list of entities associated with the database within the annotation.
  • Contain an abstract method that has 0 arguments and returns the class that is annotated with @Dao.
  At runtime, you can acquire an instance of Database by calling Room.databaseBuilder() orRoom.inMemoryDatabaseBuilder().
• Entity: Represents a table within the database.   

1. tableName attribute is used to define the name of the table
2. Every entity class must have at-least one Primary Key field, annotated with @PrimaryKey
3. Fields in entity class can be annotated with @ColumnInfo(name = “name_of_column”) annotation to give specific column names

     
• DAO: Contains the methods used for accessing the database.

1. Data Access Object is either be an interface or an abstract class annotated with @Doa annotation, containing all the methods to define the operations to be performed on data. The methods can be annotated with
   
   • @Query to retrieve data from database
   • @Insert to insert data into database
   • @Delete to delete data from database
   • @Update to update data in database

                                 

How to Implement?

Before jump into details, Room uses annotations heavily to decrease the boilerplate code.