What database do you use in your projects?

Realm and Room.

Realm

• Cross-platform (Android, iOS, React Native, Xamarin).
• Object-oriented, does not require ORM.
• Fast data handling on the fly.
• Support for reactive streams.
• Synchronization between devices.

Room

• Data persistence library, an abstraction over SQLite.
• Part of Android Architecture Components.
• Provides ORM abstraction for easy work with SQLite.
• Compilation for SQL query validation.
• Uses LiveData or Flow for reactive data retrieval.

// Example of using Room
@Entity
data class User(
    @PrimaryKey val id: Int,
    val name: String,
    val age: Int
)

@Dao
interface UserDao {
    @Query("SELECT * FROM user")
    fun getAll(): List<User>

    @Insert
    fun insertAll(vararg users: User)
}

The choice between them depends on project requirements: need for synchronization, performance, cross-platform capabilities, and team familiarity with the technologies.