一、Mybatis 常用注解
這幾年來注解開發(fā)越來越流行，Mybatis也可以使用注解開發(fā)方式，這樣我們就可以減少編寫Mapper映射文件了
- @Insert：實現(xiàn)新增
- @Update：實現(xiàn)更新
- @Delete：實現(xiàn)刪除
- @Select：實現(xiàn)查詢
- @Result：實現(xiàn)結(jié)果集封裝
- @Results：可以與@Result ?起使用，封裝多個結(jié)果集
- @One：實現(xiàn)?對?結(jié)果集封裝
- @Many：實現(xiàn)?對多結(jié)果集封裝
二、MyBatis 基于注解方式的增刪改查
- mapper 接口編寫
public interface UserMapper {
List<User> findAll();
@Insert("insert into user values(#{id},#{username})")
void insert(User user);
@Update("update user set username = #{username} where id = #{id}")
void update(User user);
@Select("select * from user")
List<User> selectList();
@Delete("delete from user where id = #{id}")
void deleteById(Integer id);
}
- 測試類編寫
package com.wujun.test;
import com.wujun.mapper.UserMapper;
import com.wujun.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class MybatisTest {
private UserMapper userMapper;
private SqlSession sqlSession;
@Before
public void before() throws IOException {
InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
sqlSession = sqlSessionFactory.openSession();
userMapper = sqlSession.getMapper(UserMapper.class);
}
@After
public void after() {
sqlSession.close();
}
@Test
public void insert() throws IOException {
User insert = new User();
insert.setId(99);
insert.setUsername("吳俊99");
userMapper.insert(insert);
sqlSession.commit();
System.out.println("新增之后=======");
List<User> users = userMapper.selectList();
for (User user : users) {
System.out.println(user);
}
}
@Test
public void update() {
User update = new User();
update.setId(99);
update.setUsername("吳俊00");
userMapper.update(update);
sqlSession.commit();
System.out.println("更新之后=======");
List<User> users2 = userMapper.selectList();
for (User user : users2) {
System.out.println(user);
}
}
@Test
public void delete() {
userMapper.deleteById(99);
sqlSession.commit();
System.out.println("刪除之后========");
List<User> users3 = userMapper.selectList();
for (User user : users3) {
System.out.println(user);
}
}
}
- 測試結(jié)果
刪除之后========
User(id=1, username=吳俊1, roles=null)
User(id=2, username=吳俊2, roles=null)
User(id=3, username=吳俊3, roles=null)
新增之后=======
User(id=1, username=吳俊1, roles=null)
User(id=2, username=吳俊2, roles=null)
User(id=3, username=吳俊3, roles=null)
User(id=99, username=吳俊99, roles=null)
更新之后=======
User(id=1, username=吳俊1, roles=null)
User(id=2, username=吳俊2, roles=null)
User(id=3, username=吳俊3, roles=null)
User(id=99, username=吳俊00, roles=null)
三、Mybatis 基于注解實現(xiàn)復(fù)雜映射開發(fā)
| 注解 | 說明 |
|---|---|
| @Results | 代替的是標(biāo)簽<resultMap> 該注解中可以使用單個@Result注解，也可以使用@Result集合 使用格式：@Results ( { @Result(), @Result() } ) 或者 @Results (@Result()) |
| @Result | 代替了<id>標(biāo)簽和<result>標(biāo)簽 @Result中的屬性介紹 column：數(shù)據(jù)庫的列名 property：需要裝配的屬性名 one：需要使用@One注解 (@Result (one = @One) （）) many：需要使用@Many注解（@Result（many = @Many）（）） |
| @One（一對一） | 代替了<assocation>標(biāo)簽，是多表查詢的關(guān)鍵，在注解中用來指定子查詢返回單一對象 @One注解屬性介紹 select：指定用來多表查詢的sqlmapper 使用格式：@Result（property= "", column="", one=@One（select=""）） |
| @Many（多對一） | 代替了<collection>標(biāo)簽，是多表查詢的關(guān)鍵，在注解中用來指定子查詢返回的對象集合 使用格式：@Result（property="", column="", many=@Many（select=""）） |
1. 一對一查詢
- javaBean：訂單里面有一個User對象，對訂單來說，一筆訂單只可能有一個用戶
@Data
public class User {
private Integer id;
private String username;
}
@Data
public class Order {
private Integer id;
private String orderName;
private User user;
}
- mapper接口
public interface OrderMapper {
@Select("select * from `order`") // 查詢所有的訂單
@Results({
@Result(id = true, property = "id", column = "id"), // 封裝訂單對象里面的id
@Result(property = "orderName", column = "order_name"), // 封裝訂單對象里面的orderName
// 以訂單對象中的 user_id 為條件，執(zhí)行com.wujun.mapper.UserMapper中的findById方法，傳參就是user_id，
// 將返回結(jié)果封裝到訂單對象的user屬性中
@Result(property = "user", column = "user_id", javaType = User.class,
one = @One(select = "com.wujun.mapper.UserMapper.findById"))
})
List<Order> findAll();
}
public interface UserMapper {
List<User> findAll();
@Insert("insert into user values(#{id},#{username})")
void insert(User user);
@Update("update user set username = #{username} where id = #{id}")
void update(User user);
@Select("select * from user")
List<User> selectList();
@Delete("delete from user where id = #{id}")
void deleteById(Integer id);
@Select("select * from `user` where id = #{id}")
User findById(Integer id);
}
- 測試類
@Test
public void findAllOrder() {
List<Order> all = orderMapper.findAll();
for (Order order : all) {
System.out.println(order);
}
}
- 測試結(jié)果
Order(id=1, orderName=訂單1, user=User(id=1, username=吳俊1))
Order(id=2, orderName=訂單2, user=User(id=2, username=吳俊2))
Order(id=3, orderName=訂單3, user=User(id=1, username=吳俊1))
2. 一對多查詢
- JavaBean：一個用戶對應(yīng)多張訂單的場景
@Data
public class User {
private Integer id;
private String username;
private List<Order> orders;
}
@Data
public class Order {
private Integer id;
private String orderName;
}
- mapper 接口編寫
public interface UserMapper {
@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.wujun.mapper.OrderMapper.findByUserId"))
})
List<User> findAll();
}
public interface OrderMapper {
@Select("select * from `order` where user_id = #{userId}")
@Results({
@Result(property = "id", column = "id"),
@Result(property = "orderName", column = "order_name")
})
List<Order> findByUserId(Integer userId);
}
- 測試類編寫
@Test
public void oneToMany() {
List<User> all = userMapper.findAll();
for (User user : all) {
System.out.println(user);
}
}
- 測試結(jié)果
User(id=1, username=吳俊1, orders=[Order(id=1, orderName=訂單1), Order(id=3, orderName=訂單3)])
User(id=2, username=吳俊2, orders=[Order(id=2, orderName=訂單2)])
User(id=3, username=吳俊3, orders=[])
User(id=99, username=吳俊00, orders=[])
