@Query for custom JPQL in Spring Boot

Introduction

The @Query annotation lets you write your own database queries in Java code. It helps when you want to get data in a special way that the usual methods can't do.

You want to find records using a complex condition not covered by method names.

You need to join multiple tables and fetch specific fields.

You want to write a query with sorting or grouping that is not automatic.

You want to update or delete records with a custom query.

You want to optimize performance by writing a precise query.

Syntax

Spring Boot

@Query("JPQL query here")
ReturnType methodName(Parameters);

JPQL is like SQL but works with Java entity names and fields, not table names.

Place @Query above repository interface methods.

Examples

Find a user by email using a custom JPQL query.

Spring Boot

@Query("SELECT u FROM User u WHERE u.email = ?1")
User findByEmail(String email);

Find users older than a certain age using a named parameter.

Spring Boot

@Query("SELECT u FROM User u WHERE u.age > :age")
List<User> findUsersOlderThan(@Param("age") int age);

Update users' status with a custom update query. Requires @Modifying.

Spring Boot

@Query("UPDATE User u SET u.status = 'ACTIVE' WHERE u.lastLogin < :date")
@Modifying
int activateOldUsers(@Param("date") LocalDate date);

Sample Program

This example shows a repository method using @Query to find users older than a given age. It uses a named parameter :age and returns a list of users.

Spring Boot

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
import java.util.List;

@Entity
public class User {
    @Id
    private Long id;
    private String name;
    private String email;
    private int age;
    // getters and setters
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    @Query("SELECT u FROM User u WHERE u.age > :age")
    List<User> findUsersOlderThan(@Param("age") int age);
}

// In a service or test class:
// List<User> users = userRepository.findUsersOlderThan(30);
// This returns all users older than 30 years.

Important Notes

Always use entity names and field names in JPQL, not database table or column names.

For update or delete queries, add @Modifying annotation and run inside a transaction.

Use @Param to name parameters clearly and avoid confusion.

Summary

@Query lets you write custom JPQL queries in Spring Data repositories.

Use it when method names can't express the query you want.

Remember to use entity names and parameters properly for clear and working queries.

Practice

1. What is the main purpose of using @Query annotation in Spring Data JPA?

easy

A. To write custom JPQL or SQL queries when default methods are insufficient

B. To automatically generate database tables

C. To configure database connection properties

D. To define entity relationships

Solution

1. Step 1: Understand default query methods

   Spring Data JPA provides default query methods like findById, but they are limited.

2. Step 2: Role of @Query

   @Query allows writing custom JPQL or SQL queries to handle complex or specific data retrieval needs.

3. Final Answer:

   To write custom JPQL or SQL queries when default methods are insufficient -> Option A

4. Quick Check:

   @Query purpose = custom queries [OK]

Hint: Remember @Query is for custom queries beyond defaults [OK]

Common Mistakes:

• Thinking @Query creates tables
• Confusing @Query with database config
• Assuming @Query defines entity relations

2. Which of the following is the correct syntax to define a custom JPQL query using @Query in a Spring Data JPA repository interface?

easy

A. @Query("SELECT u FROM User u WHERE u.name = :name") List<User> findByName(@Param("name") String name);

B. @Query(SELECT * FROM User WHERE name = :name) List<User> findByName(String name);

C. @Query("SELECT * FROM User WHERE name = ?1") List<User> findByName(String name);

D. @Query("FROM User WHERE name = ?") List<User> findByName(@Param("name") String name);

Solution

1. Step 1: Check JPQL syntax

   JPQL uses entity names and fields, not table names or * syntax.

2. Step 2: Parameter binding

   Named parameters use :paramName and must be linked with @Param("paramName") in method.

3. Final Answer:

   @Query("SELECT u FROM User u WHERE u.name = :name") List<User> findByName(@Param("name") String name); -> Option A

4. Quick Check:

   JPQL + named param + @Param = correct syntax [OK]

Hint: Use entity names and :param with @Param for correct JPQL [OK]

Common Mistakes:

• Using SQL syntax (*) instead of JPQL
• Missing @Param annotation for named parameters
• Using positional parameters incorrectly

3. Given the repository method:

@Query("SELECT u FROM User u WHERE u.age > :minAge")
List<User> findUsersOlderThan(@Param("minAge") int minAge);

What will be the result of calling findUsersOlderThan(30)?

medium

A. A list of User entities with age less than 30

B. A list of User entities with age equal to 30

C. A list of User entities with age greater than 30

D. A runtime error due to missing parameter

Solution

1. Step 1: Analyze the JPQL query

   The query selects users where age is greater than the parameter minAge.

2. Step 2: Understand method call

   Calling findUsersOlderThan(30) sets minAge to 30, so users older than 30 are returned.

3. Final Answer:

   A list of User entities with age greater than 30 -> Option C

4. Quick Check:

   minAge=30, query > minAge = users older than 30 [OK]

Hint: Check parameter value and query condition carefully [OK]

Common Mistakes:

• Confusing > with >= or =
• Assuming parameter is ignored
• Expecting users younger than 30

4. Identify the error in the following repository method:

@Query("SELECT u FROM User u WHERE u.email = :email")
List<User> findByEmail(String email);

medium

A. JPQL query uses wrong entity name

B. Missing @Param annotation for the email parameter

C. Return type should be User, not List<User>

D. Query should use native SQL syntax

Solution

1. Step 1: Check parameter binding

   The query uses a named parameter :email, so the method parameter must have @Param("email") annotation.

2. Step 2: Validate other parts

   Entity name User is correct, return type List<User> is valid, and JPQL syntax is correct.

3. Final Answer:

   Missing @Param annotation for the email parameter -> Option B

4. Quick Check:

   Named param requires @Param annotation [OK]

Hint: Always add @Param for named parameters in @Query [OK]

Common Mistakes:

• Omitting @Param causes runtime errors
• Confusing JPQL with native SQL
• Assuming return type must be single entity

5. You want to write a custom JPQL query using @Query to find all users whose name contains a given substring (case insensitive). Which of the following method definitions correctly achieves this?

hard

A. @Query("SELECT u FROM User u WHERE u.name LIKE :namePart") List<User> findByNameLike(@Param("namePart") String namePart);

B. @Query("SELECT u FROM User u WHERE u.name LIKE '%:namePart%'") List<User> findByNameContains(@Param("namePart") String namePart);

C. @Query("SELECT u FROM User u WHERE u.name = :namePart") List<User> findByNameExact(@Param("namePart") String namePart);

D. @Query("SELECT u FROM User u WHERE LOWER(u.name) LIKE LOWER(CONCAT('%', :namePart, '%'))") List<User> findByNameContainsIgnoreCase(@Param("namePart") String namePart);

Solution

1. Step 1: Understand case insensitive search

   Use LOWER() on both field and parameter to ignore case.

2. Step 2: Use LIKE with wildcards

   Concatenate '%' before and after parameter to find substring matches.

3. Step 3: Check parameter binding

   Named parameter :namePart is linked with @Param("namePart") correctly.

4. Final Answer:

   @Query("SELECT u FROM User u WHERE LOWER(u.name) LIKE LOWER(CONCAT('%', :namePart, '%'))") List<User> findByNameContainsIgnoreCase(@Param("namePart") String namePart); -> Option D

5. Quick Check:

   LOWER + LIKE + CONCAT + @Param = correct case-insensitive contains [OK]

Hint: Use LOWER() and CONCAT('%', param, '%') for case-insensitive contains [OK]

Common Mistakes:

• Using LIKE with parameter inside quotes disables binding
• Not using LOWER() for case insensitivity
• Using = instead of LIKE for substring search