Specification pattern for dynamic queries in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does Specification combine multiple conditions?

Given two Specification objects combined with and(), what is the resulting behavior when querying the database?

Spring Boot

Specification<User> spec1 = (root, query, cb) -> cb.equal(root.get("status"), "ACTIVE");
Specification<User> spec2 = (root, query, cb) -> cb.greaterThan(root.get("age"), 18);
Specification<User> combined = spec1.and(spec2);
List<User> results = userRepository.findAll(combined);

A Returns users who are either ACTIVE or older than 18.

B Returns users who are ACTIVE but ignores age condition.

C Returns users older than 18 but ignores status condition.

D Returns users who are ACTIVE and older than 18.

💡 Hint

Think about how the and() method combines conditions logically.

The and() method combines two specifications so that both conditions must be true for a record to be included. Here, only users who are ACTIVE and older than 18 are returned.

📝 Syntax

intermediate

Identify the syntax error in this Specification

Which option contains a syntax error in the Specification lambda expression?

Spring Boot

Specification<Product> spec = (root, query, cb) -> cb.like(root.get("name"), "%phone%");

A ;)"%enohp%" ,)"eman"(teg.toor(ekil.bc >- )bc ,yreuq ,toor( = ceps >tcudorP<noitacificepS

B Specification<Product> spec = (root, query, cb) -> cb.like(root.get("name"), "%phone%");

C Specification<Product> spec = (root, query, cb) -> cb.like(root.get("name"), "%phone%")

D pecification<Product> spec = (root, query, cb) -> cb.like(root.get("name"), "%phone%");

💡 Hint

Check for missing or misplaced characters in the lambda expression.

All options are identical and syntactically correct. This is a trick question to confirm understanding that the given code is valid.

🔧 Debug

advanced

Why does this Specification cause a runtime error?

Consider this Specification code snippet. What causes the runtime error?

Spring Boot

Specification<Order> spec = (root, query, cb) -> cb.equal(root.get("nonExistentField"), "value");
List<Order> orders = orderRepository.findAll(spec);

A The field 'nonExistentField' does not exist in the Order entity, causing a runtime exception.

B The Specification lambda is missing a return statement.

C The query parameter is null, causing a NullPointerException.

D The CriteriaBuilder 'cb' is not initialized properly.

💡 Hint

Check if the field used in the query matches the entity's fields.

Accessing a field that does not exist in the entity causes a runtime error because the query cannot be constructed properly.

❓ state_output

advanced

What is the result count of this dynamic Specification query?

Given this Specification that filters users by optional parameters, what is the count of users returned if both parameters are null?

Spring Boot

Specification<User> spec = Specification.where(null);
if (name != null) {
  spec = spec.and((root, query, cb) -> cb.like(root.get("name"), "%" + name + "%"));
}
if (email != null) {
  spec = spec.and((root, query, cb) -> cb.equal(root.get("email"), email));
}
List<User> users = userRepository.findAll(spec);

A Returns users filtered by default criteria.

B Throws NullPointerException due to null Specification.

C Returns all users without filtering.

D Returns no users because Specification is null.

💡 Hint

Think about what happens when Specification.where(null) is used with no further conditions.

Starting with Specification.where(null) means no filtering. If no conditions are added, the query returns all records.

🧠 Conceptual

expert

Why use Specification pattern for dynamic queries in Spring Data JPA?

Which is the best explanation for using the Specification pattern for dynamic queries?

A It allows building complex queries by combining reusable predicates dynamically at runtime.

B It automatically caches all queries to improve performance without extra code.

C It replaces the need for any JPQL or SQL queries in the application.

D It forces all queries to be static and predefined at compile time.

💡 Hint

Consider how dynamic conditions can be combined in a flexible way.

The Specification pattern enables composing query conditions dynamically and reusing them, which is ideal for complex and flexible filtering.