Room queries (Insert, Update, Delete, Select) in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new user into the Room database.

Android Kotlin

suspend fun addUser(user: User) {
  userDao.[1](user)
}

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

AinsertUser

BsaveUser

Cinsert

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names like 'add' or 'saveUser' which are not standard in Room DAO.

Confusing insert with update or delete methods.

The correct Room DAO method to insert a record is 'insert'.

2fill in blank

medium

Complete the code to update an existing user in the Room database.

Android Kotlin

suspend fun updateUser(user: User) {
  userDao.[1](user)
}

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

Aupdate

Bmodify

Cchange

Dedit

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-standard method names like 'modify' or 'edit'.

Mixing up update with insert or delete.

The correct Room DAO method to update a record is 'update'.

3fill in blank

hard

Fix the error in the delete function to remove a user from the Room database.

Android Kotlin

suspend fun deleteUser(user: User) {
  userDao.[1](user)
}

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

Adelete

Bremove

CdeleteUser

Derase

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names like 'remove' or 'erase' which are not standard in Room DAO.

Confusing delete with insert or update.

The correct Room DAO method to delete a record is 'delete'.

4fill in blank

hard

Fill both blanks to write a query that selects all users ordered by their name.

Android Kotlin

@Query("SELECT * FROM users ORDER BY [1] [2]")
suspend fun getAllUsers(): List<User>

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

Aname

BASC

CDESC

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' instead of 'name' for ordering by name.

Using 'DESC' when ascending order is intended.

To order users by name ascending, use 'name' and 'ASC'.

5fill in blank

hard

Fill all three blanks to write a query that selects users with age greater than 18 ordered by age descending.

Android Kotlin

@Query("SELECT * FROM users WHERE [1] [2] 18 ORDER BY [3] DESC")
suspend fun getAdultUsers(): List<User>

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

Aage

B>

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong column names like 'name' for filtering by age.

Using '<' instead of '>' for filtering adults.

The query filters users where age > 18 and orders by age descending.

Practice

1. Which Room annotation is used to add a new record to the database?

easy

A. @Query

B. @Insert

C. @Delete

D. @Update

Solution

1. Step 1: Understand Room annotations for data changes

   @Insert is used to add new data, @Update modifies existing data, and @Delete removes data.

2. Step 2: Identify the annotation for adding records

   Since adding means inserting new data, @Insert is the correct annotation.

3. Final Answer:

   @Insert -> Option B

4. Quick Check:

   Add new record = @Insert [OK]

Hint: Insert means add new data, so use @Insert [OK]

Common Mistakes:

• Confusing @Update with adding new data
• Using @Delete instead of @Insert
• Thinking @Query inserts data

2. Which of the following is the correct syntax to delete a user by ID using @Query in Room?

easy

A. @Query("DELETE users WHERE id = :userId")

B. @Query("REMOVE FROM users WHERE id = :userId")

C. @Query("DELETE FROM users WHERE id = :userId")

D. @Query("DELETE * FROM users WHERE id = :userId")

Solution

1. Step 1: Recall SQL DELETE syntax

   The correct SQL command to delete rows is DELETE FROM table WHERE condition.

2. Step 2: Match correct syntax in options

   @Query("DELETE FROM users WHERE id = :userId") matches the correct SQL syntax with parameter binding (:userId).

3. Final Answer:

   @Query("DELETE FROM users WHERE id = :userId") -> Option C

4. Quick Check:

   DELETE FROM table WHERE condition = correct syntax [OK]

Hint: Use 'DELETE FROM' not 'REMOVE' or 'DELETE *' [OK]

Common Mistakes:

• Using REMOVE instead of DELETE
• Omitting FROM keyword
• Adding * after DELETE

3. Given the DAO method below, what will be the return type when calling getAllUsers()?

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

medium

A. An integer count of users

B. A single User object

C. A Boolean indicating success

D. A list of User objects

Solution

1. Step 1: Analyze the method signature

   The method returns List<User>, which means a list of User objects.

2. Step 2: Understand the SQL query

   SELECT * FROM users returns all rows, so the method returns multiple User objects in a list.

3. Final Answer:

   A list of User objects -> Option D

4. Quick Check:

   Return type List<User> means multiple users [OK]

Hint: Return type List<User> means multiple users returned [OK]

Common Mistakes:

• Thinking it returns a single User
• Confusing return type with count
• Expecting a Boolean result

4. Identify the error in this Room DAO update method:

@Update
fun updateUser(user: User): Int {
  return 1
}

medium

A. The method should not have a body; it must be abstract

B. The method should return Unit, not Int

C. The method must not have a return statement

D. The @Update annotation is missing parameters

Solution

1. Step 1: Understand Room DAO method requirements

   DAO methods with @Update must be abstract or interface methods without a body.

2. Step 2: Identify the error in the method

   This method has a body with a return statement, which is not allowed for Room DAO annotated methods.

3. Final Answer:

   The method should not have a body; it must be abstract -> Option A

4. Quick Check:

   Room DAO methods are abstract, no method body [OK]

Hint: Room DAO methods must be abstract, no method body [OK]

Common Mistakes:

• Adding method body in DAO interface
• Returning wrong types intentionally
• Missing @Update annotation

5. You want to update a user's email by their ID using Room. Which DAO method below correctly performs this update?

hard

A. @Query("UPDATE users SET email = :email WHERE id = :userId")
fun updateEmail(userId: Int, email: String)

B. @Update
fun updateEmail(userId: Int, email: String)

C. @Insert(onConflict = OnConflictStrategy.REPLACE)
fun updateEmail(userId: Int, email: String)

D. @Delete
fun updateEmail(userId: Int, email: String)

Solution

1. Step 1: Understand update options in Room

   @Update requires a full entity object, so partial updates need @Query with SQL.

2. Step 2: Check which method updates email by ID

   @Query("UPDATE users SET email = :email WHERE id = :userId") fun updateEmail(userId: Int, email: String) uses @Query with SQL UPDATE statement and parameters for userId and email, which is correct.

3. Final Answer:

   @Query("UPDATE users SET email = :email WHERE id = :userId") fun updateEmail(userId: Int, email: String) -> Option A

4. Quick Check:

   Partial update needs @Query with SQL UPDATE [OK]

Hint: Use @Query with UPDATE for partial field changes [OK]

Common Mistakes:

• Using @Update without full entity
• Using @Insert to update data
• Using @Delete for updates