Spring Data JPA 简介

什么是Spring Data JPA？

Spring Data JPA是Spring Data系列中的重要一员，他帮助我们能够更简单的实现基于JPA的数据访问。免去写CRUD的痛苦。

还记得当年写hibernate的CRUD吗？

public class AppTest {

    private static final String PERSISTENCE_UNIT_NAME = "psunit1";
    private static EntityManagerFactory factory;

    public static void main(String[] args) {
        factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
        EntityManager em = factory.createEntityManager();

        em.getTransaction().begin();
        
        Product product = new Product();
        product.setProductName("JPA 2.1 Book");
        product.setProductDescription("This is the latest book on JPA 2.1");
        product.setStockQty(100.00);
        product.setPrice(95.99);
        em.persist(product);
        em.getTransaction().commit();
        em.close();
        
    }
}

如果换成JPA呢？

interface PersonRepository extends CrudRepository<User, Long> {

 Person save(Person person);
}

简单到想哭 （T T）

只要继承Spring Data JPA的Repository，然后按照Spring Data JPA的要求写方法名，一切都妥妥的了。

Keyword	例子	sql
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	findByAgeIn(Collection<Age> ages)	… where x.age in ?1
NotIn	findByAgeNotIn(Collection<Age> 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)

Spring Data JPA除了能够支持方法名的方式，还可以通过加注解的方式来实现。

• 使用HQL

public interface UserRepository extends JpaRepository<User, Long> {

  @Query("select u from User u where u.emailAddress = ?1")
  User findByEmailAddress(String emailAddress);
}

• 使用native(SQL)

public interface UserRepository extends JpaRepository<User, Long> {

  @Query(value = "SELECT * FROM USERS WHERE LASTNAME = ?1",
    countQuery = "SELECT count(*) FROM USERS WHERE LASTNAME = ?1",
    nativeQuery = true)
  Page<User> findByLastname(String lastname, Pageable pageable);
}

Transactional

Spring有自己的事务注解。

@Transactional(readOnly = true)
public interface UserRepository extends JpaRepository<User, Long> {

  List<User> findByLastname(String lastname);

  @Modifying
  @Transactional
  @Query("delete from User u where u.active = false")
  void deleteInactiveUsers();
}

Transectional 注解主要有4个重要的属性

• Isolation
• Propagation
• Timeout
• Read-only状态