3. MyBatis获取参数值的两种方式
两种方式:${}和#{}
-
${}
的本质就是字符串拼接,#{}
的本质就是占位符赋值 -
${}
使用字符串拼接的方式拼接sql,若为字符串类型或日期类型的字段进行赋值时,需要手动加单引号;但是#{}
使用占位符赋值的方式拼接sql,此时为字符串类型或日期类型的字段进行赋值时,可以自动添加单引号3
3.1 代码结构
这里pom.xml、jdbc.properties、log4j.xml、mybatis-config.xml文件不变,延用第二章的
3.1.1mapper
ParameterMapper.java
package com.atguigu.mybatis.mapper;
import com.atguigu.mybatis.pojo.User;
public interface ParameterMapper {
/**
* 验证登录(使用@Param)
*/
User checkLoginByParam(@Param("username") String username, @Param("password") String password);
/**
* 添加用户信息
*/
int insertUser(User user);
/**
* 验证登录(参数为map)
*/
User checkLoginByMap(Map<String, Object> map);
/**
* 验证登录
*/
User checkLogin(String username, String password);
/**
* 根据用户名查询用户信息
*/
User getUserByUsername(String username);
/**
* 查询所有的员工信息
*/
List<User> getAllUser();
}
3.1.2 pojo
User.java
package com.atguigu.mybatis.pojo;
public class User {
private Integer id;
private String username;
private String password;
private Integer age;
private String sex;
private String email;
//这里省略了有参无参构造、get、set、toString重载
}
3.1.3 utils
SqlSessionUtils.java
package com.atguigu.mybatis.utils;
public class SqlSessionUtils {
public static SqlSession getSqlSession(){
SqlSession sqlSession = null;
try {
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
sqlSession = sqlSessionFactory.openSession(true);
} catch (IOException e) {
e.printStackTrace();
}
return sqlSession;
}
}
3.2 映射文件和测试编写
ParameterMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.mapper.ParameterMapper">
<!--List<User> getAllUser();-->
<select id="getAllUser" resultType="User">
select * from t_user
</select>
<!--User getUserByUsername(String username);-->
<select id="getUserByUsername" resultType="User">
<!--select * from t_user where username = #{username}-->
select * from t_user where username = '${username}'
</select>
<!--User checkLogin(String username, String password);-->
<select id="checkLogin" resultType="User">
<!--select * from t_user where username = #{arg0} and password = #{arg1}-->
select * from t_user where username = '${param1}' and password = '${param2}'
</select>
<!--User checkLoginByMap(Map<String, Object> map);-->
<select id="checkLoginByMap" resultType="User">
select * from t_user where username = #{username} and password = #{password}
</select>
<!--int insertUser(User user);-->
<insert id="insertUser">
insert into t_user values(null,#{username},#{password},#{age},#{sex},#{email})
</insert>
<!--User checkLoginByParam(@Param("username") String username, @Param("password") String password);-->
<select id="checkLoginByParam" resultType="User">
select * from t_user where username = #{username} and password = #{password}
</select>
</mapper>
ParameterMapperTest.java
package com.atguigu.mybatis.test;
import com.atguigu.mybatis.mapper.ParameterMapper;
import com.atguigu.mybatis.pojo.User;
import com.atguigu.mybatis.utils.SqlSessionUtils;
public class ParameterMapperTest {
/**
* MyBatis获取参数值的两种方式:${}和#{}
* ${}本质字符串拼接
* #{}本质占位符赋值
* MyBatis获取参数值的各种情况:
* 1、mapper接口方法的参数为单个的字面量类型
* 可以通过${}和#{}以任意的名称获取参数值,但是需要注意${}的单引号问题
* 2、mapper接口方法的参数为多个时
* 此时MyBatis会将这些参数放在一个map集合中,以两种方式进行存储
* a>以arg0,arg1...为键,以参数为值
* b>以param1,param2...为键,以参数为值
* 因此只需要通过#{}和${}以键的方式访问值即可,但是需要注意${}的单引号问题
* 3、若mapper接口方法的参数有多个时,可以手动将这些参数放在一个map中存储
* 只需要通过#{}和${}以键的方式访问值即可,但是需要注意${}的单引号问题
* 4、mapper接口方法的参数是实体类类型的参数
* 只需要通过#{}和${}以属性的方式访问属性值即可,但是需要注意${}的单引号问题
* 5、使用@Param注解命名参数
* 此时MyBatis会将这些参数放在一个map集合中,以两种方式进行存储
* a>以@Param注解的值为键,以参数为值
* b>以param1,param2...为键,以参数为值
* 因此只需要通过#{}和${}以键的方式访问值即可,但是需要注意${}的单引号问题
*/
@Test
public void testCheckLoginByParam(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
User user = mapper.checkLoginByParam("admin", "123456");
System.out.println(user);
}
@Test
public void testInsertUser(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
int result = mapper.insertUser(new User(null, "李四", "123", 23, "男", "123@qq.com"));
System.out.println(result);
}
@Test
public void testCheckLoginByMap(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
Map<String, Object> map = new HashMap<>();
map.put("username", "admin");
map.put("password", "123456");
User user = mapper.checkLoginByMap(map);
System.out.println(user);
}
@Test
public void testCheckLogin(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
User user = mapper.checkLogin("admin", "123456");
System.out.println(user);
}
@Test
public void testGetUserByUsername(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
User user = mapper.getUserByUsername("admin");
System.out.println(user);
}
@Test
public void testGetAllUser(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
List<User> list = mapper.getAllUser();
list.forEach(user -> System.out.println(user));
}
@Test
public void testJDBC() throws Exception {
String username = "admin";
Class.forName("");
Connection connection = DriverManager.getConnection("", "", "");
//PreparedStatement ps = connection.prepareStatement("select * from t_user where username = '" + username + "'");
PreparedStatement ps = connection.prepareStatement("selelt * from t_user where username = ?");
ps.setString(1, username);
}
}
详解如下:
3.2.1 单个字面量类型的参数
/**
* 根据用户名查询用户信息
*/
User getUserByUsername(String username);
- 若mapper接口中的方法参数为单个的字面量类型,此时可以使用${}和#{}以任意的名称(最好见名识意)获取参数的值,注意${}需要手动加单引号
<!--User getUserByUsername(String username);-->
<select id="getUserByUsername" resultType="User">
select * from t_user where username = #{username}
</select>
<!--User getUserByUsername(String username);-->
<select id="getUserByUsername" resultType="User">
select * from t_user where username = '${username}'
</select>
@Test
public void testGetUserByUsername(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
User user = mapper.getUserByUsername("admin");
System.out.println(user);
}
3.2.2 多个字面量类型的参数
/**
* 验证登录
*/
User checkLogin(String username, String password);
@Test
public void testCheckLogin(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
User user = mapper.checkLogin("admin", "123456");
System.out.println(user);
}
若mapper接口中的方法参数为多个时,此时MyBatis会自动将这些参数放在一个map集合中
1. 以arg0,arg1...为键,以参数为值;
2. 以param1,param2...为键,以参数为值;
- 因此只需要通过${}和#{}访问map集合的键就可以获取相对应的值,注意${}需要手动加单引号。
- 使用arg或者param都行,要注意的是,arg是从arg0开始的,param是从param1开始的
<!--User checkLogin(String username,String password);-->
<select id="checkLogin" resultType="User">
select * from t_user where username = #{arg0} and password = #{arg1}
</select>
<!--User checkLogin(String username,String password);-->
<select id="checkLogin" resultType="User">
select * from t_user where username = '${param1}' and password = '${param2}'
</select>
3.2.3 map集合类型的参数
/**
* 验证登录(参数为map)
*/
User checkLoginByMap(Map<String, Object> map);
若mapper接口中的方法需要的参数为多个时,此时可以手动创建map集合,将这些数据放在map中只需要通过${}和#{}访问map集合的键就可以获取相对应的值,注意${}需要手动加单引号
<!--User checkLoginByMap(Map<String,Object> map);-->
<select id="checkLoginByMap" resultType="User">
select * from t_user where username = #{username} and password = #{password}
</select>
@Test
public void checkLoginByMap() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
Map<String,Object> map = new HashMap<>();
map.put("usermane","admin");
map.put("password","123456");
User user = mapper.checkLoginByMap(map);
System.out.println(user);
}
3.2.4 实体类类型的参数
/**
* 添加用户信息
*/
int insertUser(User user);
若mapper接口中的方法参数为实体类对象时此时可以使用${}和#{},通过访问实体类对象中的属性名获取属性值,注意${}需要手动加单引号
<!--int insertUser(User user);-->
<insert id="insertUser">
insert into t_user values(null,#{username},#{password},#{age},#{sex},#{email})
</insert>
@Test
public void insertUser() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
User user = new User(null,"Tom","123456",12,"男","123@321.com");
mapper.insertUser(user);
}
3.2.5 使用@Param标识参数
- 可以通过@Param注解标识mapper接口中的方法参数,此时,会将这些参数放在map集合中
- 以@Param注解的value属性值为键,以参数为值;
- 以param1,param2…为键,以参数为值;
- 只需要通过${}和#{}访问map集合的键就可以获取相对应的值,注意${}需要手动加单引号
<!--User CheckLoginByParam(@Param("username") String username, @Param("password") String password);-->
<select id="CheckLoginByParam" resultType="User">
select * from t_user where username = #{username} and password = #{password}
</select>
@Test
public void checkLoginByParam() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
ParameterMapper mapper = sqlSession.getMapper(ParameterMapper.class);
mapper.CheckLoginByParam("admin","123456");
}
3.2.6 总结
- 建议分成两种情况进行处理
- 实体类类型的参数
- 使用@Param标识参数
4. MyBatis的各种查询功能
4.1 代码结构
配置文件等延用第三章,这里对mapper/SelectMapper.java、resources/SelectMapper.xml、test/SelectMapperTest.java进行编写
4.1.1 mapper
SelectMapper.java
package com.atguigu.mybatis.mapper;
import com.atguigu.mybatis.pojo.User;
public interface SelectMapper {
/**
* 根据id查询用户信息
*/
List<User> getUserById(@Param("id") Integer id);
/**
* 查询所有的用户信息
*/
List<User> getAllUser();
/**
* 查询用户信息的总记录数
*/
Integer getCount();
/**
* 根据id查询用户信息为一个map集合
*/
Map<String, Object> getUserByIdToMap(@Param("id") Integer id);
/**
* 查询所有用户信息为map集合
*/
//List<Map<String, Object>> getAllUserToMap();
@MapKey("id")
Map<String, Object> getAllUserToMap();
}
4.2 映射文件和测试编写
SelectMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.mapper.SelectMapper">
<!--User getUserById(@Param("id") Integer id);-->
<select id="getUserById" resultType="User">
select * from t_user where id = #{id}
</select>
<!--List<User> getAllUser();-->
<select id="getAllUser" resultType="User">
select * from t_user
</select>
<!--Integer getCount();-->
<select id="getCount" resultType="_int">
select count(*) from t_user
</select>
<!--Map<String, Object> getUserByIdToMap(@Param("id") Integer id);-->
<select id="getUserByIdToMap" resultType="map">
select * from t_user where id = #{id}
</select>
<!--Map<String, Object> getAllUserToMap();-->
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>
</mapper>
SelectMapperTest.java
package com.atguigu.mybatis.test;
import com.atguigu.mybatis.mapper.SelectMapper;
import com.atguigu.mybatis.utils.SqlSessionUtils;
public class SelectMapperTest {
/**
* MyBatis的各种查询功能:
* 1、若查询出的数据只有一条
* a>可以通过实体类对象接收
* b>可以通过list集合接收
* c>可以通过map集合接收
* 结果:{password=123456, sex=男, id=3, age=23, email=12345@qq.com, username=admin}
* 2、若查询出的数据有多条
* a>可以通过实体类类型的list集合接收
* b>可以通过map类型的list集合接收
* c>可以在mapper接口的方法上添加@MapKey注解,此时就可以将每条数据转换的map集合作为值,以某个字段的值作为键,放在同一个map集合中
* 注意:一定不能通过实体类对象接收,此时会抛异常TooManyResultsException
*
* MyBatis中设置了默认的类型别名
* java.lang.Integer-->int,integer
* int-->_int,_integer
* Map-->map
* String-->string
*/
@Test
public void testGetAllUserToMap(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getAllUserToMap());
}
@Test
public void testGetUserByIdToMap(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getUserByIdToMap(3));
}
@Test
public void testGetCount(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getCount());
}
@Test
public void testGetAllUser(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getAllUser());
}
@Test
public void testGetUserById(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getUserById(3));
}
}
- 如果查询出的数据只有一条,可以通过
- 实体类对象接收
- List集合接收
- Map集合接收,结果
{password=123456, sex=男, id=1, age=23, username=admin}
- 如果查询出的数据有多条,一定不能用实体类对象接收,会抛异常TooManyResultsException,可以通过
- 实体类类型的LIst集合接收
- Map类型的LIst集合接收
- 在mapper接口的方法上添加@MapKey注解
4.2.1 查询一个实体类对象
/**
* 根据用户id查询用户信息
* @param id
* @return
*/
User getUserById(@Param("id") int id);
<!--User getUserById(@Param("id") int id);-->
<select id="getUserById" resultType="User">
select * from t_user where id = #{id}
</select>
@Test
public void testGetUserById(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getUserById(3));
}
4.2.2 查询所有实体类对象
/**
* 查询所有的用户信息
*/
List<User> getAllUser();
<!--List<User> getAllUser();-->
<select id="getAllUser" resultType="User">
select * from t_user
</select>
@Test
public void testGetAllUser(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getAllUser());
}
4.2.3 查询单个数据
/**
* 查询用户的总记录数
* @return
* 在MyBatis中,对于Java中常用的类型都设置了类型别名
* 例如:java.lang.Integer-->int|integer
* 例如:int-->_int|_integer
* 例如:Map-->map,List-->list
*/
int getCount();
<!--int getCount();-->
<select id="getCount" resultType="_integer">
select count(id) from t_user
</select>
@Test
public void testGetCount(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
System.out.println(mapper.getCount());
}
4.2.4 查询一条数据为map集合
Map<String, Object> getUserToMap(@Param("id") int id);
<!--Map<String, Object> getUserToMap(@Param("id") int id);-->
<select id="getUserToMap" resultType="map">
select * from t_user where id = #{id}
</select>
<!--结果:{password=123456, sex=男, id=1, age=23, username=admin}-->
4.2.5 查询多条数据为map集合
方法一
/**
* 查询所有用户信息为map集合
* @return
* 将表中的数据以map集合的方式查询,一条数据对应一个map;若有多条数据,就会产生多个map集合,此时可以将这些map放在一个list集合中获取
*/
List<Map<String, Object>> getAllUserToMap();
<!--Map<String, Object> getAllUserToMap();-->
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>
<!--
结果:
[{password=123456, sex=男, id=1, age=23, username=admin},
{password=123456, sex=男, id=2, age=23, username=张三},
{password=123456, sex=男, id=3, age=23, username=张三}]
-->
方法二
/**
* 查询所有用户信息为map集合
* @return
* 将表中的数据以map集合的方式查询,一条数据对应一个map;若有多条数据,就会产生多个map集合,并且最终要以一个map的方式返回数据,此时需要通过@MapKey注解设置map集合的键,值是每条数据所对应的map集合
*/
@MapKey("id")
Map<String, Object> getAllUserToMap();
<!--Map<String, Object> getAllUserToMap();-->
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>
<!--
结果:
{
1={password=123456, sex=男, id=1, age=23, username=admin},
2={password=123456, sex=男, id=2, age=23, username=张三},
3={password=123456, sex=男, id=3, age=23, username=张三}
}
-->
5. 特殊SQL的执行
5.1 代码结构
对SQLMapper.java、SQLMapper.xml、SQLMapperTest.java进行编写 ,其他代码延用上面的
5.1.1 mapper
SQLMapper.java
package com.atguigu.mybatis.mapper;
import com.atguigu.mybatis.pojo.User;
public interface SQLMapper {
/**
* 根据用户名模糊查询用户信息
*/
List<User> getUserByLike(@Param("username") String username);
/**
* 批量删除
*/
int deleteMore(@Param("ids") String ids);
/**
* 查询指定表中的数据
*/
List<User> getUserByTableName(@Param("tableName") String tableName);
/**
* 添加用户信息
*/
void insertUser(User user);
}
5.2 映射文件和测试编写
SQLMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.mapper.SQLMapper">
<!--List<User> getUserByLike(@Param("username") String username);-->
<select id="getUserByLike" resultType="User">
<!--select * from t_user where username like '%${username}%'-->
<!--select * from t_user where username like concat('%',#{username},'%')-->
select * from t_user where username like "%"#{username}"%"
</select>
<!--int deleteMore(@Param("ids") String ids);-->
<delete id="deleteMore">
delete from t_user where id in (${ids})
</delete>
<!--List<User> getUserByTableName(@Param("tableName") String tableName);-->
<select id="getUserByTableName" resultType="User">
select * from ${tableName}
</select>
<!--
void insertUser(User user);
useGeneratedKeys:设置当前标签中的sql使用了自增的主键
keyProperty:将自增的主键的值赋值给传输到映射文件中参数的某个属性
-->
<insert id="insertUser" useGeneratedKeys="true" keyProperty="id">
insert into t_user values(null,#{username},#{password},#{age},#{sex},#{email})
</insert>
</mapper>
SQLMapperTest.java
package com.atguigu.mybatis.test;
import com.atguigu.mybatis.mapper.SQLMapper;
import com.atguigu.mybatis.pojo.User;
import com.atguigu.mybatis.utils.SqlSessionUtils;
public class SQLMapperTest {
@Test
public void testGetUserByLike(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
List<User> list = mapper.getUserByLike("a");
System.out.println(list);
}
@Test
public void testDeleteMore(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
int result = mapper.deleteMore("1,2,3");
System.out.println(result);
}
@Test
public void testGetUserByTableName(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
List<User> list = mapper.getUserByTableName("t_user");
System.out.println(list);
}
@Test
public void testInsertUser(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
User user = new User(null, "王五", "123", 23, "男", "123@163.com");
mapper.insertUser(user);
System.out.println(user);
}
@Test
public void testJDBC() throws Exception {
Class.forName("");
Connection connection = DriverManager.getConnection("", "", "");
PreparedStatement ps = connection.prepareStatement("insert", Statement.RETURN_GENERATED_KEYS);
ps.executeUpdate();
ResultSet resultSet = ps.getGeneratedKeys();
}
}
5.2.1 模糊查询like
/**
* 根据用户名进行模糊查询
* @param username
* @return java.util.List<com.atguigu.mybatis.pojo.User>
* @date 2022/2/26 21:56
*/
List<User> getUserByLike(@Param("username") String username);
<!--List<User> getUserByLike(@Param("username") String username);-->
<select id="getUserByLike" resultType="User">
<!--select * from t_user where username like '%${mohu}%'-->
<!--select * from t_user where username like concat('%',#{mohu},'%')-->
select * from t_user where username like "%"#{mohu}"%"
</select>
- 其中
select * from t_user where username like "%"#{mohu}"%"
是最常用的
@Test
public void testGetUserByLike(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
List<User> list = mapper.getUserByLike("a");
System.out.println(list);
}
5.2.2 批量删除
只能使用${},如果使用#{},则解析后的sql语句为delete from t_user where id in ('1,2,3')
,这样是将1,2,3
看做是一个整体,只有id为1,2,3
的数据会被删除。正确的语句应该是delete from t_user where id in (1,2,3)
,或者delete from t_user where id in ('1','2','3')
/**
* 根据id批量删除
* @param ids
* @return int
* @date 2022/2/26 22:06
*/
int deleteMore(@Param("ids") String ids);
<delete id="deleteMore">
delete from t_user where id in (${ids})
</delete>
//测试类
@Test
public void deleteMore() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
int result = mapper.deleteMore("1,2,3,8");
System.out.println(result);
}
5.2.3 动态设置表名
只能使用**${}**,因为表名不能加单引号
/**
* 查询指定表中的数据
* @param tableName
* @return java.util.List<com.atguigu.mybatis.pojo.User>
* @date 2022/2/27 14:41
*/
List<User> getUserByTableName(@Param("tableName") String tableName);
<!--List<User> getUserByTableName(@Param("tableName") String tableName);-->
<select id="getUserByTableName" resultType="User">
select * from ${tableName}
</select>
@Test
public void testGetUserByTableName(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
List<User> list = mapper.getUserByTableName("t_user");
System.out.println(list);
}
5.2.4 添加功能获取自增的主键
使用场景
- t_clazz(clazz_id,clazz_name)
- t_student(student_id,student_name,clazz_id)
- 添加班级信息
- 获取新添加的班级的id
- 为班级分配学生,即将某学的班级id修改为新添加的班级的id
- 在mapper.xml中设置两个属性
- useGeneratedKeys:设置使用自增的主键
- keyProperty:因为增删改有统一的返回值是受影响的行数,因此只能将获取的自增的主键放在传输的参数user对象的某个属性中
/**
* 添加用户信息
* @param user
* @date 2022/2/27 15:04
*/
void insertUser(User user);
<!--void insertUser(User user);-->
<insert id="insertUser" useGeneratedKeys="true" keyProperty="id">
insert into t_user values (null,#{username},#{password},#{age},#{sex},#{email})
</insert>
//测试类
@Test
public void insertUser() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
User user = new User(null, "ton", "123", 23, "男", "123@321.com");
mapper.insertUser(user);
System.out.println(user);
//输出:user{id=10, username='ton', password='123', age=23, sex='男', email='123@321.com'},自增主键存放到了user的id属性中
}