1、我们的业务是如果带了id就用id查，如果带了lastName就用lastName查，只会进入进入一个查询。在DAO中顶一个方法：
package com.gwolf.dao;
import java.util.Map;
import org.apache.ibatis.annotations.MapKey;
import com.gwolf.bean.Employee;
public interface EmployeeMapper {
public List<Employee> getEmpsByConditionChoose(Employee employee);
}
2、在xml中定义choose的sql语句定义。
<select id="getEmpsByConditionChoose" resultMap="MyEmpByStep" databaseId="mysql">
select *
from tbl_emp
<where>
<choose>
<when test="empId!=null">
emp_id = #{empId}
</when>
<when test="empName!=null">
emp_name = #{empName}
</when>
</choose>
</where>
3、编写junit单元测试方法：
@Test
public void test1() throws Exception {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
Employee employee = new Employee();
employee.setEmpId(1);
List<Employee> employees = employeeMapper.getEmpsByConditionChoose(employee);
System.out.println(employees);
}finally {
sqlSession.close();
}
}
4、当我们只根据员工id查询的时候，我们的sql只会查询出员工的where子句，运行单元结果，查看控制台sql语句
5、编写根据员工和姓名查询的junit单元测试方法：
@Test
public void test1() throws Exception {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
Employee employee = new Employee();
employee.setEmpId(1);
employee.setEmpName("曹");
List<Employee> employees = employeeMapper.getEmpsByConditionChoose(employee);
System.out.println(employees);
}finally {
sqlSession.close();
}
}
6、当我们查询条件员工id和员工姓名的时候，我们的sql也只会查询出员工的where子句，运行单元测试，查看后台sql语句打印结果。
