JpaRepository interface in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a repository interface that extends JpaRepository.

Spring Boot

public interface UserRepository extends [1]<User, Long> {}

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

ARepository

BCrudRepository

CJpaRepository

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using CrudRepository instead of JpaRepository loses some JPA-specific features.

Using Repository directly does not provide method implementations.

The JpaRepository interface provides JPA related methods for standard data access operations.

2fill in blank

medium

Complete the code to add a method that finds users by their email in the repository interface.

Spring Boot

List<User> findBy[1](String email);

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

AId

BName

CUsername

DEmail

Attempts:

3 left

💡 Hint

Common Mistakes

Using a field name that does not exist in the entity.

Not capitalizing the first letter of the field in the method name.

Spring Data JPA derives queries from method names. 'findByEmail' searches by the email field.

3fill in blank

hard

Fix the error in the repository method declaration to correctly find users by status.

Spring Boot

List<User> findByStatus[1](String status);

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

AWith

BIs

CBy

DEquals

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'By' after 'findByStatus' is redundant and causes errors.

Using 'With' is not recognized by Spring Data JPA.

'findByStatusIs' is a valid Spring Data JPA method name to find by status field equality.

4fill in blank

hard

Complete the code to create a repository method that finds users with age greater than a value.

Spring Boot

List<User> findByAge[1](int age);

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

AGreaterThan

BLessThan

C, Pageable pageable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'LessThan' instead of 'GreaterThan' changes the query logic.

Adding Pageable parameter when not needed.

'findByAgeGreaterThan' finds users older than the given age. No extra parameter is needed here.

5fill in blank

hard

Fill all three blanks to define a repository method that finds users by last name and orders by first name ascending.

Spring Boot

List<User> findBy[1]OrderBy[2][3](String lastName);

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

ALastName

BFirstName

CAsc

DDesc

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Desc' instead of 'Asc' changes the order direction.

Mixing up the filter and order fields.

This method finds users by last name and orders the results by first name in ascending order.

Practice

1. What is the primary purpose of the JpaRepository interface in Spring Boot?

easy

A. To provide built-in methods for database operations on entities

B. To define the structure of REST API endpoints

C. To manage application security and authentication

D. To handle frontend UI rendering

Solution

1. Step 1: Understand JpaRepository role

   JpaRepository is designed to simplify database access by providing ready-made methods like save, findAll, and delete for entity classes.

2. Step 2: Compare with other options

   Options A, C, and D relate to REST API endpoints, security, and UI rendering, which are not responsibilities of JpaRepository.

3. Final Answer:

   To provide built-in methods for database operations on entities -> Option A

4. Quick Check:

   JpaRepository = database helper [OK]

Hint: JpaRepository = database methods for entities [OK]

Common Mistakes:

• Confusing JpaRepository with REST controllers
• Thinking it manages security
• Assuming it handles UI rendering

2. Which of the following is the correct way to declare a repository interface for an entity User with primary key type Long using JpaRepository?

easy

A. public interface UserRepository extends Repository<User> {}

B. public class UserRepository implements JpaRepository {}

C. public interface UserRepository extends JpaRepository {}

D. public interface UserRepository extends JpaRepository {}

Solution

1. Step 1: Check JpaRepository declaration syntax

   JpaRepository is an interface that should be extended, not implemented. The generic parameters are , so is correct.

2. Step 2: Validate each option

   public interface UserRepository extends JpaRepository {} correctly extends JpaRepository with . public class UserRepository implements JpaRepository {} incorrectly uses implements and class. public interface UserRepository extends JpaRepository {} swaps generic types. public interface UserRepository extends Repository<User> {} uses Repository, not JpaRepository.

3. Final Answer:

   public interface UserRepository extends JpaRepository {} -> Option D

4. Quick Check:

   Extend JpaRepository [OK]

Hint: Extend JpaRepository interface [OK]

Common Mistakes:

• Using implements instead of extends
• Swapping generic type order
• Using Repository instead of JpaRepository

3. Given the following repository method declaration:

List<User> findByLastName(String lastName);

What will this method do when called with findByLastName("Smith")?

medium

A. Return all User entities with lastName exactly 'Smith'

B. Return all User entities with lastName containing 'Smith'

C. Return a single User entity with lastName 'Smith'

D. Throw a runtime error because the method is invalid

Solution

1. Step 1: Understand method naming convention

   JpaRepository supports query derivation by method names. 'findByLastName' means find all entities where lastName equals the given parameter.

2. Step 2: Analyze return type and behavior

   The return type is List<User>, so it returns all matching users with lastName exactly 'Smith'. It does not do partial matching or throw errors.

3. Final Answer:

   Return all User entities with lastName exactly 'Smith' -> Option A

4. Quick Check:

   findByProperty = exact match [OK]

Hint: findByX = exact match, returns list if List type [OK]

Common Mistakes:

• Assuming it does partial matching
• Expecting a single result instead of list
• Thinking method is invalid without @Query

4. Consider this repository interface:

public interface ProductRepository extends JpaRepository {
    List<Product> findByPriceGreaterThan(Double price);
}

Which of the following is a likely cause of a runtime error when calling findByPriceGreaterThan(null)?

medium

A. JpaRepository does not support comparison keywords like GreaterThan

B. Method name is invalid and causes compile error

C. Passing null causes a NullPointerException in the query generation

D. The return type List<Product> is incorrect

Solution

1. Step 1: Check method name and support

   JpaRepository supports keywords like GreaterThan for query derivation, so method name is valid and compiles fine.

2. Step 2: Analyze passing null parameter

   Passing null to a comparison query causes a NullPointerException at runtime because the query cannot compare with null.

3. Final Answer:

   Passing null causes a NullPointerException in the query generation -> Option C

4. Quick Check:

   Null param in comparison query = runtime error [OK]

Hint: Never pass null to comparison query methods [OK]

Common Mistakes:

• Thinking method name is invalid
• Assuming JpaRepository lacks GreaterThan support
• Believing return type causes error

5. You want to add a custom method to your OrderRepository that finds all orders placed between two dates. Which of the following method signatures correctly uses JpaRepository naming conventions to achieve this?

hard

A. List<Order> findOrdersBetweenDates(LocalDate start, LocalDate end);

B. List<Order> findByOrderDateBetween(LocalDate start, LocalDate end);

C. List<Order> getOrdersByDateRange(LocalDate start, LocalDate end);

D. List<Order> findByOrderDateRange(LocalDate start, LocalDate end);

Solution

1. Step 1: Recall JpaRepository method naming rules

   JpaRepository supports keywords like Between to filter values between two parameters. The property name must match entity field, here 'OrderDate'.

2. Step 2: Evaluate each method signature

   List<Order> findByOrderDateBetween(LocalDate start, LocalDate end); uses 'findByOrderDateBetween' which is correct. Options B, C, and D use unsupported or incorrect keywords and will not work.

3. Final Answer:

   List<Order> findByOrderDateBetween(LocalDate start, LocalDate end); -> Option B

4. Quick Check:

   Use Between keyword for range queries [OK]

Hint: Use 'Between' keyword for range queries in method name [OK]

Common Mistakes:

• Using unsupported keywords like 'Range' or 'BetweenDates'
• Not matching property name exactly
• Trying to create custom method without @Query but wrong name