Room queries (Insert, Update, Delete, Select) in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Room query?

Given this DAO function, what will be the result of calling getAllUsers() if the database has 3 users?

Android Kotlin

import androidx.room.*

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

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

A A list of 3 User objects

B A list of 0 User objects

C A single User object

D A Cursor object

💡 Hint

The query selects all rows from the User table.

The @Query annotation with 'SELECT * FROM User' returns all rows as a list of User objects.

📝 Syntax

intermediate

Which option correctly inserts a User into the database?

Select the correct DAO function to insert a User object into the Room database.

Android Kotlin

import androidx.room.*

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

@Dao
interface UserDao {
  // Insert function here
}

A

@Query("INSERT INTO User VALUES(:user)")
fun insertUser(user: User)

B

@Insert
fun insertUser(user: User)

C fun insertUser(user: User) { database.insert(user) }

D

@Update
fun insertUser(user: User)

💡 Hint

Use the Room annotation designed for inserting entities.

The @Insert annotation tells Room to generate code to insert the entity. Option B is invalid SQL syntax, C is not Room syntax, and D uses @Update which is for updating, not inserting.

❓ lifecycle

advanced

What happens if you update a User with a non-existing ID?

Consider this DAO update function. What will happen if you call it with a User object whose ID does not exist in the database?

Android Kotlin

@Update
fun updateUser(user: User): Int

A A new User is inserted with that ID

B The function returns 1 and updates a random row

C The function returns 0 and no rows are updated

D The function throws an exception

💡 Hint

Think about how Room handles updates when no matching row exists.

Room's @Update returns the number of rows updated. If no row matches the primary key, it returns 0 and does not insert a new row.

🔧 Debug

advanced

Why does this delete query cause a runtime error?

This DAO delete function causes a runtime crash. What is the cause?

Android Kotlin

@Query("DELETE FROM User WHERE id = :userId")
fun deleteUser(userId: Int)

A The function must return Int for number of rows deleted

B The User entity does not have an id field

C The DELETE query syntax is invalid

D The userId parameter type should be Int, not String

💡 Hint

Check the data type of the primary key in the User entity.

If the User entity's id is Int, passing a String parameter causes a type mismatch at runtime.

🧠 Conceptual

expert

How does Room handle conflicts on insert with @Insert(onConflict = OnConflictStrategy.REPLACE)?

If you insert a User with an existing primary key using @Insert(onConflict = OnConflictStrategy.REPLACE), what happens?

A The existing row is replaced with the new User data

B The insert is ignored and the old row remains unchanged

C A SQLiteConstraintException is thrown

D Both rows exist causing duplicate primary keys

💡 Hint

Consider what REPLACE means in SQLite conflict strategies.

REPLACE deletes the existing row with the same primary key and inserts the new row, effectively replacing it.