这篇文章主要介绍了Mybatis基础回顾与高级应用,本文内容有点小长，希望大家耐心阅读，此文结合实例代码给大家介绍的非常详细，需要的朋友可以参考下
Mybatis基础回顾与高级应用
数据库:mysql5.7
jdk:15
引入依赖
org.mybatis mybatis 3.4.5 mysql mysql-connector-java 5.1.6 runtime junit junit 4.12 org.projectlombok lombok 1.18.22
User实体
@Data public class User { private Integer id; private String username; }jdbc.properties
jdbc.driver=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql://127.0.0.1/zdy_mybatis jdbc.username=root jdbc.password=root
sqlMapConfig.xml
案例一-查询用户
UserMapper.xml
@Test public void test1() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession // 默认开启一个事务，但是该事务不会自动提交 //在进行增删改操作时，要手动提交事务 SqlSession sqlSession = sqlSessionFactory.openSession(); //4.sqlSession调用方法：查询所有selectList 查询单个：selectOne 添加：insert 修改：update 删除：delete List users = sqlSession.selectList("user.findAll"); users.forEach(item ->{ System.out.println(item); }); sqlSession.close(); } 输出结果
User(id=1, username=Tom)
User(id=2, username=Jerry)
案例二-添加用户
UserMapper.xml
insert into user Values (#{id},#{username})
@Test public void test2() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); User user = new User(); user.setId(3); user.setUsername("jack"); sqlSession.insert("user.saveUser",user); sqlSession.commit(); sqlSession.close(); }数据库结果:
案例三-编辑用户
UserMapper.xml
update user set username = #{username} where id = #{id}
@Test public void test3() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); User user = new User(); user.setId(3); user.setUsername("rose"); sqlSession.update("user.updateUser",user); sqlSession.commit(); sqlSession.close(); }数据库结果:
案例四-删除用户
UserMapper.xml
delete from user where id =#{id}
@Test public void test4() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); User user = new User(); user.setId(3); sqlSession.delete("user.deleteUser",3); sqlSession.commit(); sqlSession.close(); }数据库结果:
传统开发方式
public interface IUserDao { //查询所有用户 List findAll() throws IOException; } UserDaoImpl
public class UserDaoImpl implements IUserDao { @Override public List findAll() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); List users = sqlSession.selectList("user.findAll"); sqlSession.close(); return users; } } @Test public void test5() throws IOException { UserDaoImpl dao = new UserDaoImpl(); List users = dao.findAll(); System.out.println(users); } 打印结果:
[User(id=1, username=Tom), User(id=2, username=Jerry)]
代理开发方式(使用JDK动态代理产生代理对象,由代理对象执行并且操作)
Mapper接口开发需要遵行以下规范:
mapper.xml文件中的namespace与mapper接口的全限定名相同;
2. mapper接口方法名和mapper.xml中定义的每个statement的id相同
3. mapper接口方法的输入参数类型和mapper.xml中定义的每个sql的parameterType的类型相同
4. mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同
根据上述的规范修改UserMapper.xml
public interface IUserDao { //查询所有用户 List findAll() throws IOException; } @Test public void test6() throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); IUserDao mapper = sqlSession.getMapper(IUserDao.class); List all = mapper.findAll(); all.forEach(item ->{ System.out.println(all); }); } 输出结果:
User(id=1, username=Tom)
User(id=2, username=Jerry)
动态sql语句 if标签
public interface IUserDao { //多条件组合查询：演示if public List findByCondition(User user); } select * from user
@Test public void test7() throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); IUserDao mapper = sqlSession.getMapper(IUserDao.class); User user1 = new User(); user1.setId(1); user1.setUsername("Tom"); List all = mapper.findByCondition(user1); for (User user : all) { System.out.println(user); } } 输出结果:
User(id=1, username=Tom)
动态sql语句 foreach标签
public interface IUserDao { //多值查询：演示foreach public List findByIds(int[] ids); } @Test public void test8() throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); IUserDao mapper = sqlSession.getMapper(IUserDao.class); int[] arr = {1,2}; List all = mapper.findByIds(arr); for (User user : all) { System.out.println(user); } } 输出结果:
User(id=1, username=Tom)
User(id=2, username=Jerry)
Mybatis复杂映射
一对一
User实体
@Data public class User { private Integer id; private String username; //该用户所具有的订单信息 private List orders; //该用户所具有的角色信息 private List roles; } Order实体
@Data public class Order { private Integer id; private String orderTime; private BigDecimal total; //表明该订单属于哪个用户 private User user; }Role实体
@Data public class Role { private Integer id; private String roleName; }public interface IOrderMapper { /** * 查询订单的同时还查询该订单所属的用户 * @return */ public List findOrderAndUser(); }
@Test public void test1() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); IOrderMapper mapper = sqlSession.getMapper(IOrderMapper.class); List orderAndUser = mapper.findOrderAndUser(); orderAndUser.forEach(order -> { System.out.println(order); }); } 运行结果:
Order(id=1, orderTime=2022-05-01, total=1000.00, user=User(id=1, username=Tom, orders=null, roles=null))
Order(id=2, orderTime=2022-05-10, total=2000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
Order(id=3, orderTime=2022-05-20, total=3000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
一对多
public interface IUserMapper { /** * 查询所有用户信息,同时查询出每个用户关联的订单信息 * @return */ public List findAll(); }
@Test public void test2() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); IUserMapper mapper = sqlSession.getMapper(IUserMapper.class); List users = mapper.findAll(); users.forEach(user -> { System.out.println(user.getUsername()); System.out.println(user.getOrders()); }); } 运行结果:
Tom
[Order(id=1, orderTime=2022-05-01, total=1000.00, user=null)]
Jerry
[Order(id=2, orderTime=2022-05-10, total=2000.00, user=null), Order(id=3, orderTime=2022-05-20, total=3000.00, user=null)]
多对多
public interface IUserMapper { /** * 查询所有用户信息,同事查询出每个用户关联的角色信息 * @return */ public List findUserAndRole(); }
@Test public void test3() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); IUserMapper mapper = sqlSession.getMapper(IUserMapper.class); List users = mapper.findUserAndRole(); users.forEach(user -> { System.out.println(user.getUsername()); System.out.println(user.getRoles()); }); } 运行结果:
Tom
[Role(id=null, roleName=董事长), Role(id=null, roleName=经理)]
Jerry
[Role(id=null, roleName=董事长), Role(id=null, roleName=经理)]
Mybatis注解开发
Mybasits常用注解:
@Insert: 实现新增 @Update: 实现更新 @Delete: 实现删除 @Select: 实现查询 @Result: 实现结果集封装;他代替的是标签,该注解中可以使用单个@Result注解,也可以使用@Result集合, 使用格式:@Results({@Result(),@Result()}) 或 @Results(@Result()) @Results: 可以与@Result一起使用,封装多个结果集 @One: 实现一对一结果集封装 @Many: 实现一对多结果集封装
测试案例
public interface IUserMapper { //添加用户 @Insert("insert into user values(#{id},#{username})") public void addUser(User user); //更新用户 @Update("update user set username = #{} where id = #{id}") public void updateUser(User user); //查询用户 @Select("select * from user") public List getAllUser(); //删除用户 @Delete("delete from user where id=#{id}") public void delUser(Integer id); } private IUserMapper mapper; @Before public void before() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession true:事务自动提交 SqlSession sqlSession = sqlSessionFactory.openSession(true); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void addUser(){ User user = new User(); user.setId(3); user.setUsername("jack"); mapper.addUser(user); } @Test public void updateUser(){ User user = new User(); user.setId(3); user.setUsername("rose"); mapper.updateUser(user); } @Test public void getAllUser(){ List userList = mapper.getAllUser(); userList.forEach(item -> { System.out.println(item); }); } @Test public void delUser(){ mapper.delUser(3); } 运行结果:
Mybatis注解实现复杂映射开发
一对一
public interface IOrderMapper { /** * 查询订单的同时还查询该订单所属的用户 * @return */ @Results({ @Result(property = "id",column = "id"), @Result(property = "orderTime",column = "order_time"), @Result(property = "total",column = "total"), @Result(property = "user",column = "uid",javaType = User.class, one = @One(select = "com.yun.mapper.IUserMapper.getUserById")), }) @Select("select * from orders") public List findOrderAndUser(); } public interface IUserMapper { @Select("select * from user where id = #{id}") public User getUserById(Integer id); } @Test public void oneToOne(){ List orderAndUser = orderMapper.findOrderAndUser(); orderAndUser.forEach(item -> { System.out.println(item); }); } 运行结果:
Order(id=1, orderTime=2022-05-01, total=1000.00, user=User(id=1, username=Tom, orders=null, roles=null))
Order(id=2, orderTime=2022-05-10, total=2000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
Order(id=3, orderTime=2022-05-20, total=3000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
一对多
public interface IUserMapper { /** * 查询所有用户信息,同时查询出每个用户关联的订单信息 * @return */ @Select("select * from user") @Results({ @Result(property = "id",column = "id"), @Result(property = "username",column = "username"), @Result(property = "orders",column = "id",javaType = List.class, many = @Many(select = "com.yun.mapper.IOrderMapper.getOrderByUid")) }) public List findAll(); } public interface IOrderMapper { @Select("select * from orders where uid = #{uid}") public List getOrderByUid(Integer uid); } @Test public void oneToMore(){ List users = mapper.findAll(); users.forEach(item -> { System.out.println(item); }); } 运行结果:
User(id=1, username=Tom, orders=[Order(id=1, orderTime=null, total=1000.00, user=null)], roles=null)
User(id=2, username=Jerry, orders=[Order(id=2, orderTime=null, total=2000.00, user=null), Order(id=3, orderTime=null, total=3000.00, user=null)], roles=null)
多对多
public interface IUserMapper { /** * 查询所有用户信息,同事查询出每个用户关联的角色信息 * @return */ @Select("select * from user") @Results({ @Result(property = "id",column = "id"), @Result(property = "username",column = "username"), @Result(property = "roles",column = "id",javaType = List.class, many = @Many(select ="com.yun.mapper.IRoleMapper.getAll")) }) public List findUserAndRole(); } public interface IRoleMapper { @Select("select * from sys_role sr,sys_user_role sur where sr.id = sur.role_id and sur.user_id = #{uid}") public List getAll(Integer uid); } @Test public void moreToMore(){ List users = mapper.findUserAndRole(); users.forEach(item -> { System.out.println(item); }); } 运行结果:
User(id=1, username=Tom, orders=null, roles=[Role(id=1, roleName=董事长), Role(id=2, roleName=经理)])
User(id=2, username=Jerry, orders=null, roles=[Role(id=1, roleName=董事长), Role(id=2, roleName=经理)])
Mybatis缓存
基础概念
缓存就是内存中的数据,常常来自对数据库查询结果的保存,使用缓存,我们可以避免频繁的与数据库进行交互,进而提高响应速度.
一级缓存是SqlSession,在操作数据库时需要构造sqlSession对象,在对象中有一个数据结构(HashMap)用于存储缓存数据.不同的sqlSession之间互不影响.
二级缓存是mapper级别的缓存,多个sqlSession去操作同一个mapper的sql语句,多个sqlSession可以共用二级缓存,二级缓存是跨sqlSession的.
一级缓存
demo
public class CacheTest { private IUserMapper mapper; private SqlSession sqlSession; @Before public void before() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession true:事务自动提交 sqlSession = sqlSessionFactory.openSession(true); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void test1() { //第一次查询id为1的用户 User user1 = mapper.getUserById(1); //第二次查询id为1的用户 User user2 = mapper.getUserById(1); System.out.println(user1 == user2); } }返回结果为 true ;测试一级缓存是默认开启的
结论:第一次发起查询用户id为1的用户信息,先去找缓存中是否有id为1的用户,如果没有,则从数据库查询用户信息,得到用户信息并且将用户信息存储到一级缓存中,第二次发起查询用户id为1的用户信息,先去找缓存中是否有id为1的用户,如果缓存中有,直接从缓存中获取用户信息;
现在我们变换一下上面的demo
public class CacheTest { private IUserMapper mapper; private SqlSession sqlSession; @Before public void before() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession true:事务自动提交 sqlSession = sqlSessionFactory.openSession(); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void test1() { //第一次查询id为1的用户 User user1 = mapper.getUserById(1); User user = new User(); user.setId(1); user.setUsername("Lucy"); mapper.updateUser(user); sqlSession.commit(); //第二次查询id为1的用户 User user2 = mapper.getUserById(1); System.out.println(user1 == user2); } }返回结果为 false
结论:做增删改操作,并进行了事物的提交,就会刷新以及缓存;或者还可以通过 sqlSession.clearCache()清楚缓存;这样做的目的就是为了让缓存中存储的是最新的信息,避免脏读;
二级缓存
二级缓存的原理和一级缓存原理一样,第一次查询会将数据放入缓存中,然后第二次查询则会直接从缓存中获取,但是一级缓存是基于sqlSession的,而二级缓存是基于mapper文件的namespace,也就是说,多个sqlSession可以共享一个mapper中的二级缓存,并且如果两个mapper的namespace相同,即使是两个mapper,那么这两个mapper执行sql查询到的数据也将存在相同的二级缓存区域中.
如何使用二级缓存
首先在全局配置文件sqlMapconfig.xml文件加入如下代码
注意,该配置需要放在properties标签下,具体顺序,可百度了解
其次,在xxxMapper.xml文件中开启缓存(如果当前操作时基于注解开发的话,使用注解@CacheNamespace)
demo2
public class CacheTest { private IUserMapper mapper; private SqlSession sqlSession; private SqlSessionFactory sqlSessionFactory; @Before public void before() throws IOException { //1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件，并创建了sqlSessionFactory工厂 sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生产sqlSession sqlSession = sqlSessionFactory.openSession(); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void test2() { SqlSession sqlSession1 = sqlSessionFactory.openSession(); SqlSession sqlSession2 = sqlSessionFactory.openSession(); SqlSession sqlSession3 = sqlSessionFactory.openSession(); IUserMapper mapper1 = sqlSession1.getMapper(IUserMapper.class); IUserMapper mapper2 = sqlSession2.getMapper(IUserMapper.class); IUserMapper mapper3 = sqlSession3.getMapper(IUserMapper.class); User user1 = mapper1.getUserById(1); //清空一级缓存 sqlSession1.close(); User user2 = mapper2.getUserById(1); System.out.println(user1 == user2); } }运行结果为 false
结论:通过debug断点显示,实际上,第二次查询则会直接从缓存中获取用户信息了,不过二级缓存缓存的不是对象,而是缓存的对象中的数据,所以查询结果为false;
注意,二级缓存底层还是HashMap结构,所以 po类需要实现序列化接口 ;因为二级缓存数据存储介质多种多样,不一定只存在内存中,有可能存在硬盘中,如果我们要在取这个缓存的话,就需要反序列化了,所以mybatis中的pojo都去实现Serializable接口;
变换一下demo2
@Test public void test2() { SqlSession sqlSession1 = sqlSessionFactory.openSession(); SqlSession sqlSession2 = sqlSessionFactory.openSession(); SqlSession sqlSession3 = sqlSessionFactory.openSession(); IUserMapper mapper1 = sqlSession1.getMapper(IUserMapper.class); IUserMapper mapper2 = sqlSession2.getMapper(IUserMapper.class); IUserMapper mapper3 = sqlSession3.getMapper(IUserMapper.class); User user1 = mapper1.getUserById(1); //清空一级缓存 sqlSession1.close(); User user = new User(); user.setId(1); user.setUsername("Tom"); mapper3.updateUser(user); sqlSession3.commit(); User user2 = mapper2.getUserById(1); System.out.println(user1 == user2); }返回结果为 false
结论:做增删改操作,并进行了事物的提交,就会刷新以及缓存;这样做的目的就是为了让缓存中存储的是最新的信息,避免脏读;
此外mybatis中还可以配置useCache和flushCache等配置项;
useCache
是用来设置是否禁用二级缓存的,在statement中设置useCache=false可以禁用当前select语句的二级缓存,即每次查询都会会发出sql去查询,默认情况是true,即该sql使用二级缓存,例如
使用sql注解方式可以使用@Options(useCache = false)的方式
flushCache
在mapper的同一个namespace中,如果有其他的insert,update,delete操作数据后需要刷新缓存,如果不执行刷新缓存会出现脏读,设置statememt配置中的
flushCache = "true"属性,默认情况下为true,即刷新缓存,如果改成false则不会刷新,使用缓存时如果手动修改数据库表中的查询数据会出现脏读 例如
一般下执行完commit操作都需要刷新缓存,flushCache=true表示刷新缓存,这样可以避免数据库脏读,所以我们不用设置,默认即可
至此,mybatis基础概念及应用回顾完成!
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