Spring Boot uses Spring Data JPA to operate the database

1 Configuration

1.1 Maven dependencies

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

1.2 Configuration properties file application.properties

spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://hostname:3306/dbName?useUnicode=true&characterEncoding=utf-8&useSSL=true&serverTimezone=UTC
spring.datasource.username=youname
spring.datasource.password=youpassword

spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

or use application.yml

spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://hostname:3306/dbName?useUnicode=true&characterEncoding=utf-8&useSSL=true&serverTimezone=UTC
    username: youname
    password: youpassword
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true

2 Write the class

2.1 Entity class

@Entity
@Table(name = "tb_user")                            // 数据库表名
public class User {
    @Id                                             // 主键
    @GeneratedValue(strategy = GenerationType.AUTO) // 自增
    private Long id;
    private String username;
    private String password;

    // setter and getter
}

2.2 Dao layers

Write an interface that inherits the JpaRepository interface, which provides common CRUD methods that can be called directly

public interface UserDao extends JpaRepository<User, Long>{
    // 自定义方法
}

2.3 Service layer

Inject UserDao

@Service
public class UserService {
    @Resource
    private UserDao userDao;

}

3 query methods

Add, delete, and modify operations using transactions (add @Transactional annotations on the corresponding methods of the Service layer or Dao layer), otherwise the following error will be reported: javax.persistence.TransactionRequiredException: Executing an update/delete query

3.1 Directly call the method of the interface JpaRepository to generate SQL

// 保存用户信息
userDao.save(user);
// 查获取所有用户信息列表
userDao.findAll();

3.2 Use @Query annotation to generate custom SQL

/**
 * 在 UserDao 中添加自定义方法
 * User 为类名，将关联到 数据库表 tb_user
 */
@Query(value = "SELECT u FROM User u")
List<User> listUser();

/**
 * 对于增、删、改类型 SQL 需要添加 @Modifying 
 * ?1: 取方法参数列表中第一个参数的值，如果方法参数有多个，?1 ?2...
 */
@Modifying
@Query(value = "DELETE FROM User WHERE id = ?1")
int removeUserByMinId(Long id);

/**
 * 多个参数
 * ?1 -> id
 * ?2 -> username
 * ?3 -> newPasswd
 */
@Modifying
@Query(value = "UPDATE User SET password = ?3 WHERE id = ?1 OR username = ?2")
void updateUserPassword(Long id, String username, String newPasswd);

/**
 * 使用命名参数，通过  ":param" 的形式引用
 */
@Modifying
@Query(value = "UPDATE User SET password = :pwd WHERE id = :id OR username = :name")
void updateUserPassword2(@Param("id") Long id, 
                        @Param("name") String username, 
                        @Param("pwd") String newPasswd);
/**
 * 引用实体类属性
 */
@Modifying
@Query(value = "UPDATE User SET password = :#{#user.password} WHERE id = :#{#user.id} OR username = :#{#user.username}")
void updateUserPassword3(@Param("user") User user);

3.3 Use keywords to create queries to generate SQL

Add method in UserDao

/**
 * 符合规则的方法将自动生成 SQL
 * <==> SELECT u FROM User u WHERE username = ?1
 */
User findByUsername(String username);

Available keywords are as follows
: https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.sample-app.finders.strategies

keywords	Example	transform into
And	findByLastnameAndFirstname	… where x.lastname = ?1 and x.firstname = ?2
Or	findByLastnameOrFirstname	… where x.lastname = ?1 or x.firstname = ?2
Is,Equals	findByFirstname，findByFirstnameIs，findByFirstnameEquals	… where x.firstname = ?1
Between	findByStartDateBetween	… where x.startDate between ?1 and ?2
LessThan	findByAgeLessThan	… where x.age < ?1
LessThanEqual	findByAgeLessThanEqual	… where x.age <= ?1
GreaterThan	findByAgeGreaterThan	… where x.age > ?1
GreaterThanEqual	findByAgeGreaterThanEqual	… where x.age >= ?1
After	findByStartDateAfter	… where x.startDate > ?1
Before	findByStartDateBefore	… where x.startDate < ?1
IsNull	findByAgeIsNull	… where x.age is null
IsNotNull,NotNull	findByAge(Is)NotNull	… where x.age not null
Like	findByFirstnameLike	… where x.firstname like ?1
NotLike	findByFirstnameNotLike	… where x.firstname not like ?1
StartingWith	findByFirstnameStartingWith	… where x.firstname like ?1 (parameter bound with appended %)
EndingWith	findByFirstnameEndingWith	… where x.firstname like ?1 (parameter bound with prepended %)
Containing	findByFirstnameContaining	… where x.firstname like ?1 (parameter bound wrapped in %)
OrderBy	findByAgeOrderByLastnameDesc	… where x.age = ?1 order by x.lastname desc
Not	findByLastnameNot	… where x.lastname <> ?1
In	findByAgeNotIn(Collection ages)	… where x.age in ?1
NotIn	findByAgeNotIn(Collection ages)	… where x.age not in ?1
True	findByActiveTrue ()	… where x.active = true
False	findByActiveFalse ()	… where x.active = false
IgnoreCase	findByFirstnameIgnoreCase	… where UPPER(x.firstame) = UPPER(?1)

4 complete code

GitHub：https://github.com/1332508387/boot-jpa