SSM（七）使用动态SQL完成多条件查询
一、目标
掌握if+where完成多条件查询
掌握if+trim完成多条件查询
二、动态SQL
基于OGNL表达式
使用动态SQL完成多条件查询等逻辑实现
用于实现动态SQL的元素主要有
- if
- trim
- where
- set
- choose(when、otherwise)
- foreach
三、if
需求说明：
改造查询用户信息列表的演示示例，增加查询条件：
- 用户角色（根据角色ID）
- 用户名称（模糊查询）
错误代码：
UserMapper.java
public List getUserListDSQL(@Param("userName")String userName, @Param("userRole")Integer roleId);
UserMapper.xml
UserMapperTest.java
@Test
public void testGetUserListDSQL() {
List userList = new ArrayList();
SqlSession sqlSession = null;
String userName = "a";
Integer userRole = 1;
try {
sqlSession = MyBatisUtil.createSqlSession();
userList = sqlSession.getMapper(UserMapper.class).getUserListDSQL(userName, userRole);
} catch(Exception e) {
e.printStackTrace();
} finally {
MyBatisUtil.closeSqlSession(sqlSession);
}
for(User _user : userList) {
logger.debug("testGetUserListDSQL userCode: " + _user.getUserCode()
+" and userName: " + _user.getUserName()
+ " and userRole: " + _user.getUserRole()
+ " and userRoleName: " + _user.getUserRoleName());
}
}
问题：
当传入用户角色参数为空的时候，查询结果为空。
分析：
正确结果：所有用户角色下的用户数据。
原因：select * from smbms_user u, smbms_role r where u.userRole=r.id and u.userName like CONCAT('%','a','%') and u.userRole=null;
如何处理：if（判断参数）：实现简单的条件判断
UserMapper.java
public List getUserListDSQL2(@Param("userName")String userName, @Param("userRole")Integer roleId);
UserMapper.xml
UserMapperTest.java
@Test
public void testGetUserListDSQL2() {
List userList = new ArrayList();
SqlSession sqlSession = null;
String userName = "a";
Integer userRole = null;
try {
sqlSession = MyBatisUtil.createSqlSession();
userList = sqlSession.getMapper(UserMapper.class).getUserListDSQL2(userName, userRole);
} catch(Exception e) {
e.printStackTrace();
} finally {
MyBatisUtil.closeSqlSession(sqlSession);
}
for(User _user : userList) {
logger.debug("testGetUserListDSQL userCode: " + _user.getUserCode()
+" and userName: " + _user.getUserName()
+ " and userRole: " + _user.getUserRole()
+ " and userRoleName: " + _user.getUserRoleName());
}
}
四、where
错误代码：
UserMapper.java
public List getUserListDSQLW(@Param("userName")String userName, @Param("userRole")Integer roleId);
UserMapper.xml
UserMapperTest.java
@Test
public void testGetUserListDSQLW() {
List userList = new ArrayList();
SqlSession sqlSession = null;
String userName = null;
Integer userRole = 3;
try {
sqlSession = MyBatisUtil.createSqlSession();
userList = sqlSession.getMapper(UserMapper.class).getUserListDSQLW(userName, userRole);
} catch(Exception e) {
e.printStackTrace();
} finally {
MyBatisUtil.closeSqlSession(sqlSession);
}
for(User _user : userList) {
logger.debug("testGetUserListDSQL userCode: " + _user.getUserCode()
+" and userName: " + _user.getUserName()
+ " and userRole: " + _user.getUserRole()
+ " and userRoleName: " + _user.getUserRoleName());
}
}
结果报错，打印SQL：
select * from smbms_user where and userRole = ?
修改UserMapper.xml
where:
简化SQL语句中where条件判断
只能处理and和or
五、trim
属性：
- prefix
- suffix
- prefixOverrides
- suffixOverrides
更灵活的去处多余的关键字
替代where
UserMapper.java
public List getUserListDSQLT(@Param("userName")String userName, @Param("userRole")Integer roleId);
UserMapper.xml
UserMapperTest.java
@Test
public void testGetUserListDSQLT() {
List userList = new ArrayList();
SqlSession sqlSession = null;
String userName = null;
Integer userRole = 1;
try {
sqlSession = MyBatisUtil.createSqlSession();
userList = sqlSession.getMapper(UserMapper.class).getUserListDSQLT(userName, userRole);
} catch(Exception e) {
e.printStackTrace();
} finally {
MyBatisUtil.closeSqlSession(sqlSession);
}
logger.debug(userList.size());
for(User _user : userList) {
logger.debug("testGetUserListDSQLW userCode: " + _user.getUserCode()
+" and userName: " + _user.getUserName()
+ " and userRole: " + _user.getUserRole());
}
}