Specification pattern for dynamic queries in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Specification that checks if a field equals a value.

Spring Boot

Specification<User> spec = (root, query, criteriaBuilder) -> criteriaBuilder.[1](root.get("username"), "john");

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

AnotEqual

Blike

CgreaterThan

Dequal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'like' instead of 'equal' for exact match.

Using 'greaterThan' which is for numeric comparisons.

The equal method creates a condition to check if the field matches the given value exactly.

2fill in blank

medium

Complete the code to combine two Specifications with AND logic.

Spring Boot

Specification<User> combinedSpec = spec1.[1](spec2);

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

Anot

Bor

Cand

Dequals

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'or' which allows either condition to be true.

Using 'not' which negates a specification.

The and method combines two specifications so both conditions must be true.

3fill in blank

hard

Fix the error in the Specification to check if age is greater than 18.

Spring Boot

Specification<User> adultSpec = (root, query, criteriaBuilder) -> criteriaBuilder.[1](root.get("age"), 18);

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

AgreaterThan

Bequal

ClessThan

Dlike

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'equal' which checks for exact match.

Using 'like' which is for strings.

The greaterThan method checks if the field value is greater than the given number.

4fill in blank

hard

Fill both blanks to create a Specification that checks if status is 'ACTIVE' and email contains 'example.com'.

Spring Boot

Specification<User> spec = Specification.where((root, query, criteriaBuilder) -> criteriaBuilder.[1](root.get("status"), "ACTIVE")).[2]((root, query, criteriaBuilder) -> criteriaBuilder.like(root.get("email"), "%example.com%"));

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

Aequal

Bor

Cand

Dnot

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'or' instead of 'and' which changes logic.

Using 'not' which negates conditions.

Use equal to check exact status and and to combine both conditions.

5fill in blank

hard

Fill all three blanks to create a Specification that filters users with age greater than 25, name starting with 'A', and active status.

Spring Boot

Specification<User> spec = Specification.where((root, query, criteriaBuilder) -> criteriaBuilder.[1](root.get("age"), 25)).[2]((root, query, criteriaBuilder) -> criteriaBuilder.like(root.get("name"), "A%"))[3]((root, query, criteriaBuilder) -> criteriaBuilder.equal(root.get("status"), "ACTIVE"));

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

AgreaterThan

Band

C.and

D.or

Attempts:

3 left

💡 Hint

Common Mistakes

Missing dot before 'and' in chaining.

Using 'or' which changes filter logic.

Use greaterThan for age, and to combine, and .and to chain the last condition.

Practice

1. What is the main purpose of the Specification pattern in Spring Boot?

easy

A. To manage application configuration properties

B. To create REST API endpoints automatically

C. To handle HTTP request routing

D. To build flexible and reusable database queries dynamically

Solution

1. Step 1: Understand the role of Specification pattern

   The Specification pattern is designed to help build database queries that can be combined and reused dynamically.

2. Step 2: Compare with other options

   Options A, C, and D relate to other Spring Boot features like configuration, routing, and REST APIs, not query building.

3. Final Answer:

   To build flexible and reusable database queries dynamically -> Option D

4. Quick Check:

   Specification pattern = flexible queries [OK]

Hint: Specification pattern builds flexible queries step-by-step [OK]

Common Mistakes:

• Confusing Specification with REST controller features
• Thinking it manages app configuration
• Assuming it handles HTTP routing

2. Which of the following is the correct method signature to implement in a Specification class in Spring Boot?

easy

A. public Predicate toPredicate(Root<T> root, CriteriaQuery query, CriteriaBuilder builder)

B. public void executeQuery(String sql)

C. public List<T> findAll()

D. public void configure()

Solution

1. Step 1: Recall Specification interface method

   The Specification interface requires implementing the toPredicate method with parameters Root, CriteriaQuery, and CriteriaBuilder.

2. Step 2: Eliminate incorrect options

   Options A, B, and C do not match the Specification interface method signature.

3. Final Answer:

   public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder) -> Option A

4. Quick Check:

   Specification method = toPredicate(...) [OK]

Hint: Specification requires toPredicate method with root, query, builder [OK]

Common Mistakes:

• Using methods unrelated to Specification interface
• Missing correct method parameters
• Confusing with repository methods

3. Given the following Specification code snippet, what will be the result of the query?

Specification<User> spec = (root, query, builder) -> builder.equal(root.get("status"), "ACTIVE");
List<User> users = userRepository.findAll(spec);

medium

A. Throws a syntax error due to lambda usage

B. Returns all users regardless of status

C. Returns all users with status 'ACTIVE'

D. Returns users with status 'INACTIVE'

Solution

1. Step 1: Analyze the Specification lambda

   The lambda creates a predicate that filters users where the 'status' field equals 'ACTIVE'.

2. Step 2: Understand the repository call

   The findAll(spec) method applies this filter, returning only users matching the predicate.

3. Final Answer:

   Returns all users with status 'ACTIVE' -> Option C

4. Quick Check:

   Predicate filters status = ACTIVE [OK]

Hint: Predicate filters users by status 'ACTIVE' [OK]

Common Mistakes:

• Assuming it returns all users without filtering
• Thinking lambda causes syntax error
• Confusing status values

4. Identify the error in this Specification implementation:

public class UserSpec implements Specification<User> {
  public Predicate toPredicate(Root<User> root, CriteriaQuery query) {
    return builder.equal(root.get("age"), 30);
  }
}

medium

A. Missing CriteriaBuilder parameter in toPredicate method

B. Incorrect return type; should return boolean

C. Root parameter type is wrong

D. Method name should be buildPredicate

Solution

1. Step 1: Check toPredicate method signature

   The Specification interface requires three parameters: Root, CriteriaQuery, and CriteriaBuilder.

2. Step 2: Identify missing parameter

   The method is missing the CriteriaBuilder parameter, so it cannot build the predicate correctly.

3. Final Answer:

   Missing CriteriaBuilder parameter in toPredicate method -> Option A

4. Quick Check:

   toPredicate needs CriteriaBuilder parameter [OK]

Hint: toPredicate must have three parameters including CriteriaBuilder [OK]

Common Mistakes:

• Omitting CriteriaBuilder parameter
• Returning wrong type
• Wrong method name

5. How can you combine two Specifications spec1 and spec2 to create a dynamic query that matches records satisfying both conditions?

hard

A. Use spec1.or(spec2)

B. Use Specification.where(spec1).and(spec2)

C. Use spec1.add(spec2)

D. Use spec1.merge(spec2)

Solution

1. Step 1: Recall Specification combination methods

   Spring Data JPA Specification provides where(), and(), and or() methods to combine Specifications logically.

2. Step 2: Combine for AND condition

   To match records satisfying both conditions, use Specification.where(spec1).and(spec2).

3. Final Answer:

   Use Specification.where(spec1).and(spec2) -> Option B

4. Quick Check:

   Combine specs with where().and() for AND logic [OK]

Hint: Use where().and() to combine Specifications with AND logic [OK]

Common Mistakes:

• Using or() instead of and() for AND condition
• Using non-existent add() or merge() methods
• Not wrapping with Specification.where()