Room database setup in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Correct Room Entity Declaration

Which option correctly declares a Room entity with a primary key named id of type Int?

A

@Entity
 data class User(
  @PrimaryKey val id: Int,
  val name: String
 )

B

@Entity
 data class User(
  val id: Int,
  @PrimaryKey val name: String
 )

C

data class User(
  @PrimaryKey val id: Int,
  val name: String
 )

D

@Entity
 data class User(
  @PrimaryKey(autoGenerate = true) val name: String,
  val id: Int
 )

💡 Hint

Remember the @Entity annotation is required on the data class and @PrimaryKey must be on the primary key property.

Option A correctly uses @Entity on the data class and marks id as the primary key. Option A wrongly marks name as primary key. Option A misses the @Entity annotation. Option A wrongly uses name as primary key and swaps property order.

❓ ui_behavior

intermediate

Room Database Builder Behavior

What happens if you call Room.databaseBuilder(context, AppDatabase::class.java, "db_name").build() multiple times in your app?

A Each call creates a new database instance, which can cause unexpected behavior and resource waste.

B Room automatically returns the same singleton instance for all calls.

C The database file is deleted and recreated each time.

D The app crashes with an IllegalStateException.

💡 Hint

Think about how Room manages database instances and best practices for usage.

Calling databaseBuilder().build() multiple times creates separate instances. This can cause conflicts and waste resources. The recommended approach is to create a singleton instance and reuse it.

❓ lifecycle

advanced

Room Database Migration Handling

If you change your Room database schema by adding a new column without providing a migration strategy, what will happen when the app runs?

A Room automatically updates the database without any issues.

B The app crashes with an IllegalStateException about missing migration.

C The app ignores the new column and continues using the old schema.

D The database is deleted and recreated silently.

💡 Hint

Room requires explicit migration strategies to handle schema changes safely.

Room enforces schema consistency. Without a migration, it throws an IllegalStateException to prevent data loss. You must provide a migration or fallback strategy.

❓ navigation

advanced

Accessing DAO from ViewModel

What is the best way to access a Room DAO inside a ViewModel in an Android app?

A Create a new database instance inside the ViewModel and get the DAO.

B Use a global variable to hold the DAO and access it inside the ViewModel.

C Pass the DAO instance to the ViewModel constructor using a ViewModelFactory.

D Access the DAO directly from the Activity and pass data to ViewModel methods.

💡 Hint

Think about separation of concerns and lifecycle safety.

Passing the DAO via ViewModelFactory keeps the ViewModel testable and lifecycle-aware. Creating new database instances or using globals can cause resource issues or tight coupling.

🧠 Conceptual

expert

Room Database Threading Behavior

Which statement best describes Room's default behavior regarding database operations and threading?

A Room queues database operations and runs them sequentially on the main thread.

B Room allows database operations on the main thread by default.

C Room automatically runs all queries on a background thread.

D Room throws an exception if you perform database operations on the main thread.

💡 Hint

Consider Android's UI thread and responsiveness rules.

Room enforces that database operations do not run on the main thread to avoid UI freezes. It throws a runtime exception if you try to do so unless you explicitly allow main thread queries (not recommended).