N+1 query problem in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the association annotation to fetch associated customers eagerly when fetching orders.

Spring Boot

@ManyToOne(fetch = [1])
private Customer customer;

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

AFetchType.EAGER

BFetchType.LAZY

CFetchType.DEFAULT

DFetchType.NONE

Attempts:

3 left

💡 Hint

Common Mistakes

Using LAZY fetch causes multiple queries for each related entity.

Using DEFAULT or NONE does not explicitly solve the N+1 problem.

Using FetchType.EAGER ensures that related entities are loaded immediately, preventing the N+1 query problem.

2fill in blank

medium

Complete the JPQL query to fetch orders with customers using a join fetch to avoid N+1 queries.

Spring Boot

SELECT o FROM Order o [1] JOIN FETCH o.customer

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

ALEFT

BFULL

CINNER

DRIGHT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT JOIN FETCH might include orders without customers.

RIGHT and FULL joins are rarely used in JPQL and may cause errors.

Using INNER JOIN FETCH fetches orders and their customers in one query, avoiding N+1 queries.

3fill in blank

hard

Fix the error in the repository method to prevent N+1 queries by adding the correct annotation.

Spring Boot

@Query("SELECT o FROM Order o [1] JOIN FETCH o.customer")
List<Order> findAllOrdersWithCustomers();

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

AINNER

BLEFT

CRIGHT

DOUTER

Attempts:

3 left

💡 Hint

Common Mistakes

Using RIGHT or OUTER join fetch causes JPQL syntax errors.

Omitting JOIN FETCH causes lazy loading and N+1 queries.

The INNER JOIN FETCH annotation in the query ensures orders and customers are fetched together, avoiding N+1 queries.

4fill in blank

hard

Fill both blanks to define a Spring Data JPA method that fetches orders with customers eagerly.

Spring Boot

List<Order> findAllBy[1]Fetch[2]();

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

ACustomer

BOrder

CEagerly

DLazy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Order' in the first blank is incorrect because the method targets customers.

Using 'Lazy' in the second blank does not solve N+1 queries.

The method name findAllByCustomerFetchEagerly suggests fetching orders with customers eagerly, helping avoid N+1 queries.

5fill in blank

hard

Fill all three blanks to complete the code that uses EntityGraph to solve the N+1 query problem.

Spring Boot

@EntityGraph(attributePaths = {"[1]"})
List<Order> findAllWith[2]();

// Usage:
List<Order> orders = orderRepository.[3]();

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

Acustomer

BCustomers

CfindAllWithCustomers

DfindAll

Attempts:

3 left

💡 Hint

Common Mistakes

Using plural 'customer' in attributePaths causes errors.

Calling 'findAll()' does not use the EntityGraph and causes N+1 queries.

Using @EntityGraph(attributePaths = {"customer"}) with method findAllWithCustomers() fetches orders with customers eagerly, avoiding N+1 queries.