Room with Coroutines in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a suspend function for inserting a user in the DAO.

Android Kotlin

suspend fun insertUser(user: User) [1]

Drag options to blanks, or click blank then click option'

A= insert(user)

B{ /* implementation */ }

C= suspendInsert(user)

D= insertUser(user)

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign a function call without suspend keyword.

Using a non-suspend function call inside a suspend function without proper handling.

The suspend function must have a body or delegate to another suspend function. Here, we use a function body placeholder.

2fill in blank

medium

Complete the DAO function to return all users as a Flow.

Android Kotlin

@Query("SELECT * FROM users")
fun getAllUsers(): [1]

Drag options to blanks, or click blank then click option'

AFlow<List<User>>

BLiveData<List<User>>

CDeferred<List<User>>

DList<User>

Attempts:

3 left

💡 Hint

Common Mistakes

Using List which is synchronous and not reactive.

Using LiveData instead of Flow when working with coroutines.

Using Flow> allows observing the database changes asynchronously with coroutines.

3fill in blank

hard

Fix the error in the suspend DAO function declaration for deleting a user.

Android Kotlin

suspend fun deleteUser(user: User) [1]

Drag options to blanks, or click blank then click option'

A{ delete(user) }

B= delete(user)

C= suspendDelete(user)

D{ suspendDelete(user) }

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign a function call without suspend keyword.

Using an undefined suspendDelete function.

The suspend function should have a function body calling the delete method. Using curly braces with the call is correct.

4fill in blank

hard

Fill both blanks to define a suspend function that updates a user in the DAO.

Android Kotlin

suspend fun updateUser(user: User) [1] update(user) [2]

Drag options to blanks, or click blank then click option'

A{

B}

Csuspend

Dfun

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting curly braces causing syntax errors.

Trying to use 'suspend' or 'fun' inside the function body.

The suspend function must have curly braces around the update call to define its body.

5fill in blank

hard

Fill all three blanks to create a DAO function that returns a Flow of users filtered by age.

Android Kotlin

@Query("SELECT * FROM users WHERE age [1] :minAge")
fun getUsersOlderThan(minAge: Int): [2] = [3]

Drag options to blanks, or click blank then click option'

A>

BFlow<List<User>>

Cflow { emitAll(query(minAge)) }

DList<User>

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operator like '<'.

Returning List instead of Flow>.

Not returning a Flow implementation.

The query uses '>' to filter users older than minAge. The function returns a Flow of user lists, implemented by emitting all results from a query flow.

Practice

1. What is the main benefit of using Coroutines with Room in Android development?

easy

A. They replace the need for SQL queries.

B. They automatically create database tables.

C. They allow database operations to run without freezing the app UI.

D. They make the app use less memory.

Solution

1. Step 1: Understand Coroutines role

   Coroutines let tasks run in the background without blocking the main app thread.

2. Step 2: Connect Coroutines with Room

   Room uses suspend functions with Coroutines to perform database operations smoothly without freezing UI.

3. Final Answer:

   They allow database operations to run without freezing the app UI. -> Option C

4. Quick Check:

   Coroutines keep UI responsive = A [OK]

Hint: Coroutines keep UI smooth by running tasks in background [OK]

Common Mistakes:

• Thinking Coroutines create tables automatically
• Believing Coroutines replace SQL queries
• Assuming Coroutines reduce app memory usage directly

2. Which of the following is the correct way to declare a suspend function in a Room DAO interface?

easy

A. suspend fun getAllUsers(): List<User>

B. fun getAllUsers(): List<User>

C. async fun getAllUsers(): List<User>

D. fun suspend getAllUsers(): List<User>

Solution

1. Step 1: Recall suspend function syntax

   A suspend function is declared with the keyword suspend before fun.

2. Step 2: Check each option

   suspend fun getAllUsers(): List<User> correctly uses suspend fun. Plain fun getAllUsers(): List<User> lacks the suspend keyword. fun suspend getAllUsers(): List<User> has the keywords in wrong order. async fun getAllUsers(): List<User> uses async which is not valid here.

3. Final Answer:

   suspend fun getAllUsers(): List<User> -> Option A

4. Quick Check:

   suspend keyword before fun = B [OK]

Hint: Remember: suspend keyword always comes before fun [OK]

Common Mistakes:

• Placing suspend after fun
• Using async instead of suspend
• Omitting suspend keyword for coroutine functions

3. Given this DAO function:

 @Query("SELECT * FROM users")
 suspend fun getUsers(): List<User>

What happens when you call getUsers() from a coroutine?

medium

A. The function blocks the main thread until data is fetched.

B. The function suspends the coroutine until data is fetched, then returns the list.

C. The function returns immediately with an empty list.

D. The function throws a compile-time error.

Solution

1. Step 1: Understand suspend function behavior

   A suspend function pauses the coroutine without blocking the thread until the result is ready.

2. Step 2: Apply to Room DAO call

   Calling getUsers() suspends the coroutine until Room fetches data, then returns the list.

3. Final Answer:

   The function suspends the coroutine until data is fetched, then returns the list. -> Option B

4. Quick Check:

   suspend functions pause coroutine, not block thread = C [OK]

Hint: Suspend functions pause coroutine, not block main thread [OK]

Common Mistakes:

• Thinking suspend blocks main thread
• Expecting immediate empty list return
• Assuming compile-time error on suspend

4. You wrote this DAO method:

@Query("SELECT * FROM users")
fun getUsers(): List<User>

When calling getUsers() from a coroutine, what problem will occur?

medium

A. The app will crash with a runtime error about main thread database access.

B. The function will suspend correctly and return data.

C. The function will return null instead of data.

D. The function will compile but never return.

Solution

1. Step 1: Identify missing suspend keyword

   The DAO method is not marked suspend, so it runs on the calling thread.

2. Step 2: Understand Room's main thread policy

   Room forbids database queries on the main thread to avoid freezing UI, causing runtime crash if violated.

3. Final Answer:

   The app will crash with a runtime error about main thread database access. -> Option A

4. Quick Check:

   Non-suspend DAO on main thread causes crash = A [OK]

Hint: Always mark DAO queries suspend to avoid main thread crash [OK]

Common Mistakes:

• Forgetting suspend keyword in DAO
• Expecting null return on wrong thread
• Assuming silent failure without crash

5. You want to insert a list of users into the database using Room and Coroutines. Which DAO method signature correctly supports this operation without blocking the UI?

@Insert
??? fun insertUsers(users: List<User>)

hard

A. fun insertUsers(users: List<User>)

B. async fun insertUsers(users: List<User>)

C. fun insertUsers(users: List<User>): Deferred<Unit>

D. suspend fun insertUsers(users: List<User>)

Solution

1. Step 1: Identify correct coroutine support

   To run database operations without blocking UI, DAO methods must be suspend functions.

2. Step 2: Evaluate options

   suspend fun insertUsers(users: List<User>) uses suspend fun, which is correct. fun insertUsers(users: List<User>) blocks UI. fun insertUsers(users: List<User>): Deferred<Unit> returns Deferred which is not standard DAO signature. async fun insertUsers(users: List<User>) uses invalid async keyword.

3. Final Answer:

   suspend fun insertUsers(users: List<User>) -> Option D

4. Quick Check:

   Use suspend fun for non-blocking Room inserts = D [OK]

Hint: Use suspend fun for DAO inserts to keep UI smooth [OK]

Common Mistakes:

• Omitting suspend causing UI freeze
• Using async keyword incorrectly
• Returning Deferred instead of suspend function