mybatis进阶操作

动态sql

<select id="findUserByCondition" resultMap="userMap" parameterType="user"> select * from user <where> <if test="userName != null"> and username = #{userName} </if> <if test="userSex != null"> and sex = #{userSex} </if> </where> </select> <!-- 根据queryvo中的Id集合实现查询用户列表 --> <select id="findUserInIds" resultMap="userMap" parameterType="queryvo"> <include refid="defaultUser"></include> <where> <if test="ids != null and ids.size()>0"> <foreach collection="ids" open="and id in (" close=")" item="uid" separator=","> #{uid} </foreach> </if> </where> </select>

UNPOOLED

在sqlmapconfig.xml中,

每次新建一个连接

POOLED

从数据库连接池中取连接

Created connection 926370398.

Returned connection 926370398 to pool.

mybatis缓存

一级缓存

一级缓存是 SqlSession 范围的缓存，当调用 SqlSession 的修改，添加，删除，commit()，close()等方

法时，就会清空一级缓存。

User user1 = userDao.findById(41); User user2 = userDao.findById(41); //两次查询为同一个对象 User user3 = userDao.findById(41); sqlSession.close(); sqlSession = factory.openSession(); User user4 = userDao.findById(41); //两次查询不是同一个对象 sqlSession.clearCache();//也可以清空缓存

二级缓存

它指的是Mybatis中SqlSessionFactory对象的缓存。由同一个SqlSessionFactory对象创建的SqlSession共享其缓存

sqlmapconfig.xml <settings> <setting name="cacheEnabled" value="true"/> </settings> UserDao.xml <!--开启user支持二级缓存--> <cache/> <select id="findById" parameterType="INT" resultType="user" useCache="true"> select * from user where id = #{uid} </select> @Before//用于在测试方法执行之前执行 public void init()throws Exception{ //1.读取配置文件，生成字节输入流 in = Resources.getResourceAsStream("SqlMapConfig.xml"); //2.获取SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in); } @After//用于在测试方法执行之后执行 public void destroy()throws Exception{ in.close(); } @Test public void testCache(){ SqlSession sqlSession1 = factory.openSession(); IUserDao dao1 = sqlSession1.getMapper(IUserDao.class); User user1 = dao1.findById(41); System.out.println(user1); sqlSession1.close();//一级缓存消失 SqlSession sqlSession2 = factory.openSession(); IUserDao dao2 = sqlSession2.getMapper(IUserDao.class); User user2 = dao2.findById(41); System.out.println(user2); sqlSession2.close(); System.out.println(user1 == user2);//两次不想等,二级缓存存储的为数据而不是对象 }

注解开发

实体类字段与数据库无法对应

@Select("select * from user") @Results(id = "userMap",value={ //数据库字段和实体类不一致时 @Result(id = true,column = "id",property = "userId"), @Result(column = "username",property = "userName"), @Result(column = "address",property = "userAddress"), @Result(column = "sex",property = "userSex"), @Result(column = "birthday",property = "userBirthday"), }) List<User> findAll(); @Select("select * from user where id = #{id}") @ResultMap(value = {"userMap"}) User finById(Integer id);

mybatis一对一查询

修改实体类

@Getter @Setter @ToString public class Account implements Serializable { private Integer id; private Integer uid; private Double money; //一对一,一个账户属于一个用户 private User user; }

AccountDao

@Select("select * from account") @Results(id = "accountMap",value = { @Result(id = true,column = "id",property = "id"), @Result(column = "uid",property = "uid"), @Result(column = "money",property = "money"), //定义一对一 , 封装对象 根据UID查 查询方法 立即加载 @Result(property = "user",column = "uid",one = @One(select="com.cc.annotation.dao.UserDao.finById",fetchType= FetchType.EAGER)) }) List<Account> findAll();

UserDao

@Select("select * from user where id = #{id}") @ResultMap(value = {"userMap"}) User finById(Integer id);

mybatis一对多

修改实体类

@Getter @Setter @ToString public class User implements Serializable { private Integer userId; private String userName; private String userSex; private String userAddress; private Date userBirthday; //一对多,一个用户对应多个账户 private List<Account> accounts;

UserDao

@Select("select * from user") @Results(id = "userMap",value={ //数据库字段和实体类不一致时 @Result(id = true,column = "id",property = "userId"), @Result(column = "username",property = "userName"), @Result(column = "address",property = "userAddress"), @Result(column = "sex",property = "userSex"), @Result(column = "birthday",property = "userBirthday"), @Result(property = "accounts",column = "id", many = @Many(select= "com.cc.annotation.dao.AccountDao.finById", fetchType= FetchType.LAZY)) }) List<User> findAll();

AccountDao

@Select("select * from account where uid = #{userId}") List<Account> finById(Integer userId);

二级缓存

在dao接口类上加注解

//@CacheNamespace(blocking = true) 开启二级缓存