android Room with kotlin value class?

Android Room with Kotlin Value Classes

Kotlin’s Value Classes offer a compelling approach to data modeling, promoting immutability and type safety. This article delves into integrating Value Classes with Android Room persistence library.

Value Classes in Kotlin

What are Value Classes?

Value classes in Kotlin are a lightweight way to represent data structures, focusing on immutability and equality based on their contents. They essentially wrap a single property, making them inherently immutable and promoting data consistency.

Key Features

• Immutability: Value classes are inherently immutable, preventing unintended modifications. This ensures data integrity and promotes thread safety.
• Equality Based on Content: Two instances of a Value Class are considered equal if their underlying values are the same.
• Lightweight: Value classes introduce minimal runtime overhead compared to traditional data classes.

Using Value Classes with Room

1. Define Value Classes

import androidx.room.Entity
import androidx.room.PrimaryKey
import androidx.room.TypeConverter

@Entity(tableName = "user_table")
data class User(
    @PrimaryKey(autoGenerate = true) val id: Int = 0,
    val name: String,
    val age: Int,
    val address: Address
)

@TypeConverter
fun addressToString(address: Address): String = address.toString()

@TypeConverter
fun stringToAddress(value: String): Address = Address.valueOf(value)

@JvmInline
value class Address(val value: String) {
    override fun toString(): String = value
    companion object {
        fun valueOf(value: String): Address = Address(value)
    }
}

2. Define Room Entities

Use Room entities as usual to define your database schema. In this case, the “User” entity includes an “Address” value class.

3. Room Type Converters

Since Room operates on basic data types, you’ll need type converters to map your Value Class to and from Room’s supported types. We create type converters for “Address” to convert it to and from a String.

4. Use in Queries

You can use Value Classes in your Room queries as regular properties. The type converters will handle the conversion between your Value Class and the database.

@Dao
interface UserDao {
    @Insert
    suspend fun insertUser(user: User)

    @Query("SELECT * FROM user_table WHERE address = :address")
    suspend fun getUserByAddress(address: Address): User
}

5. Advantages

• Immutability: Ensures data consistency and thread safety.
• Type Safety: Provides compile-time type checking for better code reliability.
• Code Readability: Value Classes make the intent of your data model clear.

Comparison with Data Classes

Conclusion

Kotlin’s Value Classes, combined with Room’s type converters, enable you to create immutable and type-safe database models in your Android applications. This enhances code quality, reduces bugs, and contributes to a more maintainable database structure.