前言
JPA（Java Persistence API）和MyBatis Plus是两种不同的持久化框架，它们具有不同的特点和适用场景。
JPA是Java官方的持久化规范，它提供了一种基于对象的编程模型，可以通过注解或XML配置来实现对象与数据库的映射关系。JPA的优点是可以对数据库进行更高级的操作，如查询、更新、删除等，同时也支持事务管理和缓存机制，能够更好地支持复杂的业务逻辑。
MyBatis Plus (MPP) 是在MyBatis基础上进行封装的增强版本，它提供了更简单易用的API和更高效的性能。MyBatis Plus通过XML或注解的方式来配置数据库映射关系，并提供了丰富的查询、更新、删除操作的方法。相对于JPA，MyBatis Plus配置简单、易于上手，同时也灵活性较高，能够更好地满足项目的特定需求。
如果只是针对单表的增删改查，两者十分相似，本质上都算ORM框架，那么到底什么时候适合用JPA，什么时候用MyBatisPlus，下面做下这两者的详细对比。
POM依赖
JPA
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
MPP
<dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId>
</dependency>
Entity定义
JPA
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.GeneratedValue;@Entity
@Table(name = "dept")
public class Dept {@Id@Column(name = "id")@GeneratedValue(strategy = GenerationType.AUTO)private Long id;@Column(name = "code")private String code;@Column(name = "name")private String name;
}
MPP
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;@TableName(value = "dept")
public class Dept {@TableId(value = "id", type = IdType.AUTO)private Long id;@TableField(value = "code")private String code;@TableField(value = "name")private String name;
}
DAO定义
基础CRUD
JPA
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;@Repository
public interface DeptRepository extends JpaRepository<Dept, Long> {
}
MPP
import org.apache.ibatis.annotations.Mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;@Mapper
public interface DeptMapper extends BaseMapper<Dept> {
}
基类主要方法
| 方法 | JpaRepository | BaseMapper |
|---|---|---|
| 插入一条记录 | save(T entity) | insert(T entity) |
| 插入多条记录 | saveAll(Iterable entities) | insertBatchSomeColumn(List entityList) |
| 根据 ID 删除 | deleteById(ID id) | deleteById(Serializable id) |
| 根据实体(ID)删除 | delete(T entity) | deleteById(T entity) |
| 根据条件删除记录 | - | delete(Wrapper queryWrapper) |
| 删除（根据ID或实体 批量删除） | deleteAllById(Iterable<? extends ID> ids) | deleteBatchIds(Collection<?> idList) |
| 根据 ID 修改 | save(T entity) | updateById(T entity) |
| 根据条件更新记录 | - | update(Wrapper updateWrapper) |
| 根据 ID 查询 | findById(ID id) | selectById(Serializable id) |
| 查询（根据ID 批量查询） | findAllById(Iterable ids) | selectBatchIds(Collection<? extends Serializable> idList) |
| 根据条件查询一条记录 | - | selectOne(Wrapper queryWrapper) |
| 根据条件判断是否存在记录 | exists(Example example) | exists(Wrapper queryWrapper) |
| 根据条件查询总记录数 | count(Example example) | selectCount(Wrapper queryWrapper) |
| 根据条件查询全部记录 | findAll(Example example, Sort sort) | selectList(Wrapper queryWrapper) |
| 根据条件查询分页记录 | findAll(Example example, Pageable pageable) | selectPage(P page, Wrapper queryWrapper) |
Example、Specification VS Wrapper
JPA使用Example和Specification 类来实现范本数据的查询，而MPP使用QueryWrapper来设置查询条件
JPA Example
Dept dept = new Dept();
dept.setCode("100");
dept.setName("Dept1");// select * from dept where code = '100' and name = 'Dept1';
List<Dept> deptList = deptRepository.findAll(Example.of(dept));
默认是生成的条件都是 “=”，如果要设置其他比较符，需要使用ExampleMatcher
Dept dept = new Dept();
dept.setCode("100");
dept.setName("Dept1");// select * from dept where code like '100%' and name like '%Dept1%';
List<Dept> deptList = deptRepository.findAll(Example.of(dept, ExampleMatcher.matching().withMatcher("code", ExampleMatcher.GenericPropertyMatchers.startsWith()).withMatcher("name", ExampleMatcher.GenericPropertyMatchers.contains())));
Example仅能实现对字符串类型的匹配模式，如果要设置其他类型的字段，可以实现JpaSpecificationExecutor接口来完成：
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.stereotype.Repository;@Repository
public interface DeptRepository extends JpaRepository<Dept, Long>, JpaSpecificationExecutor<Dept> {
}
增加以上接口后，会增加以下查询方法：
- findOne(Specification spec)
- findAll(Specification spec)
- findAll(Specification spec, Pageable pageable)
- count(Specification spec)
- exists(Specification spec)
使用示例：
Dept dept = new Dept();
dept.setCode("100");
dept.setName("Dept1");// select * from dept where code like '100%' and name like '%Dept1%';
Specification<Dept> spec = new Specification<Dept>() {@Overridepublic Predicate toPredicate(Root<Dept> root, CriteriaQuery<?> query, CriteriaBuilder cb) {List<Predicate> predicates = new ArrayList<>();// 模糊查询（前缀匹配）if (dept.getCode() != null && !dept.getCode().isEmpty()) {predicates.add(cb.like(root.get("code"), dept.getCode() + "%"));}// 模糊查询if (dept.getName() != null && !dept.getName().isEmpty()) {predicates.add(cb.like(root.get("code"), '%' + dept.getCode() + "%"));}return query.where(predicates.toArray(new Predicate[predicates.size()])).getRestriction();}
};
List<Dept> deptList = deptRepository.findAll(Example.of(dept));
除了equal、notEqual, 针对日期、数字类型，还有gt、ge、lt、le等常用比较符。
自定义接口
JPA
JPA支持接口规范方法名查询，一般查询方法以 find、findBy、read、readBy、get、getBy为前缀，JPA在进行方法解析的时候会把前缀取掉，然后对剩下部分进行解析。例如：
@Repository
public interface DeptRepository extends JpaRepository<Dept, Long> {// 调用此方法时，会自动生成 where code = ? 的条件Dept getByCode(String code);
}
常用的方法命名有：
| 关键字 | 方法命名 | sql where字句 |
|---|---|---|
| Distinct | findDistinctByLastnameAndFirstname | select distinct … where x.lastname = ?1 and x.firstname = ?2 |
| And | findByNameAndPwd | where name= ? and pwd =? |
| Or | findByNameOrSex | where name= ? or sex=? |
| Is,Equals | findById, findByIdIs, findByIdEquals | where id= ? |
| Between | findByIdBetween | where id between ? and ? |
| LessThan | findByIdLessThan | where id < ? |
| LessThanEquals | findByIdLessThanEquals | where id <= ? |
| GreaterThan | findByIdGreaterThan | where id > ? |
| GreaterThanEquals | findByIdGreaterThanEquals | where id > = ? |
| After | findByIdAfter | where id > ? |
| Before | findByIdBefore | where id < ? |
| IsNull | findByNameIsNull | where name is null |
| isNotNull,NotNull | findByNameNotNull | where name is not null |
| Like | findByNameLike | where name like ? |
| NotLike | findByNameNotLike | where name not like ? |
| StartingWith | findByNameStartingWith | where name like ‘?%’ |
| EndingWith | findByNameEndingWith | where name like ‘%?’ |
| Containing | findByNameContaining | where name like ‘%?%’ |
| OrderBy | findByIdOrderByXDesc | where id=? order by x desc |
| Not | findByNameNot | where name <> ? |
| In | findByIdIn(Collection<?> c) | where id in (?) |
| NotIn | findByIdNotIn(Collection<?> c) | where id not in (?) |
| True | findByEnabledTue | where enabled = true |
| False | findByEnabledFalse | where enabled = false |
| IgnoreCase | findByNameIgnoreCase | where UPPER(name)=UPPER(?) |
| First,Top | findFirstByOrderByLastnameAsc | order by lastname limit 1 |
| FirstN,TopN | findTop3ByOrderByLastnameAsc | order by lastname limit 3 |
MPP
MyBatisPlus没有JPA那样可以根据接口的方法名自动组装查询条件，但是可以利用Java8的接口默认实现来达到同样的目的，只不过需要编写少量的代码：
import org.apache.ibatis.annotations.Mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;@Mapper
public interface DeptMapper extends BaseMapper<Dept> {default Dept getByCode(String code) {return selectOne(Wrappers.<Dept>lambdaWrapper().eq(Dept::getCode, code));}
}
自定义SQL
JPA支持通过@Query注解和XML的形式实现自定义SQL，而MyBatis支持通过@Select、@Delete、@Update、@Script注解和XML的形式实现自定义SQL。
JPA
JPA的自定义SQL分为JPQL(Java Persistence Query Language Java 持久化查询语言)和原生SQL两种。
JPQL:
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;@Repository
public interface DeptRepository extends JpaRepository<Dept, Long> {@Query(value = "select d from Dept d where d.code = ?1")Dept getByCode(String code);@Modifying@Query(value = "delete from Dept d where d.code = :code")int deleteByCode(@Param("code") String code);
}
原生SQL
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;@Repository
public interface DeptRepository extends JpaRepository<Dept, Long> {@Query(value = "SELECT * FROM dept WHERE name = ?1", countQuery = "SELECT count(*) FROM dept WHERE name = ?1", nativeQuery = true)Page<Dept> findByName(@Param("name") String name, Pageable pageable);
}
XML形式：
/resource/META-INFO/orm.xml
<named-query name="Dept.getByCode"><query> select d from Dept d where d.code = ?1</query>
</named-query>
<named-native-query name="Dept.deleteByCode"><query> DELETE FROM dept WHERE code = ?1</query>
</named-native-query>
MyBatis
JPA的自定义SQL分为注解形式和XML形式
注解形式:
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.metadata.IPage;@Mapper
public interface DeptMapper extends BaseMapper<Dept> {@Select(value = "SELECT * FROM dept WHERE code = #{code}")Dept getByCode(@Param("code") String code);@Delete("DELETE FROM dept WHERE code = #{code}")int deleteByCode(@Param("code") String code);@Select(value = "SELECT * FROM dept WHERE name = #{name}")IPage<Dept> findByName(@Param("name") String name, IPage<Dept> page);
}
XML形式：
/resource/mapper/DeptMapper.xml
<select id = "getByCode", resultType = "Dept">SELECT * FROM dept WHERE code = #{code}
</select>
<delete id = "deleteByCode">DELETE FROM dept WHERE code = #{code}
</select>
<select id = "findByName">SELECT * FROM dept WHERE name = #{name}
</select>
］C语言函数参数背后的秘密)
