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Explanation

Spring Data JPA provides built-in query methods based on method naming conventions. Example: find user by name without writing SQL manually.

Code:

public interface UserRepository extends
 JpaRepository<User, Long> {
  User findByName(String name);
}

Explanation

You can create queries using multiple conditions by combining keywords like And, Or, Between, LessThan, GreaterThan.

Code:

List<User> findByNameAndAge(
String name, int age
);

Explanation

Use @Query annotation to write custom JPQL (Java Persistence Query Language) queries when method naming is not sufficient.

Code:

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

Explanation

JPQL works with entity class names and field names instead of table names and column names.

Code:

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

Explanation

You can write native SQL queries using nativeQuery = true when database-specific queries are required.

Code:

@Query(value = "SELECT * FROM users 
WHERE age > ?1", nativeQuery = true)
List<User> findUsersByAge(int age);

Explanation

Use positional parameters (?1, ?2) or named parameters (:name) while writing custom queries.

Code:

@Query("SELECT u FROM User u WHERE 
u.name = :name AND u.age = :age")
User findUser(@Param("name") 
String name, @Param("age") int age);

Explanation

Custom update or delete queries require @Modifying and @Transactional annotations.

Code:

@Modifying
@Transactional
@Query("UPDATE User u SET u.name 
= :name WHERE u.id = :id")

int updateUserName(@Param("id") 
Long id, @Param("name") String name);