第三章：if 判断-Mybatis合辑3-Mybatis动态SQL

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- 示例：
- EmployeeMapper.java

```
package com.sunxiaping.mapper;

import com.sunxiaping.domain.Employee;

import java.util.List;

public interface EmployeeMapper {

List<Employee> getEmpsByConditionIf(Employee employee);
}
```
- EmployeeMapper.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.sunxiaping.mapper.EmployeeMapper">
    <select id="getEmpsByConditionIf" resultType="com.sunxiaping.domain.Employee">
        SELECT id as id,last_name as lastName,gender as gender,email as email
        FROM employee
        WHERE 1 = 1
        
        <if test="id != null">
            AND id = #{id,jdbcType=INTEGER}
        </if>
        <if test="lastName != null and lastName != ''">
            AND last_name LIKE #{lastName,jdbcType=VARCHAR}
        </if>
        <if test="gender != null and gender != ''">
            AND gender = #{gender,jdbcType=VARCHAR}
        </if>
        <if test="email != null and email != ''">
            AND email = #{email,jdbcType=VARCHAR}
        </if>
    </select>
</mapper>
```
- 测试：

```
package com.sunxiaping;

import com.sunxiaping.domain.Employee;
import com.sunxiaping.mapper.EmployeeMapper;
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 EmployeeTest {
    SqlSessionFactory sqlSessionFactory = null;
    SqlSession sqlSession = null;
    EmployeeMapper employeeMapper = null;

@Before
    public void before() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession(true);
        employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
        
    }

@After
    public void after() {
        if (null != sqlSession) {
            sqlSession.close();
        }
    }

@Test
    public void testFindById() {
        Employee example = new Employee();
        example.setId(1);
        example.setGender("男");
        List<Employee> employeeList = employeeMapper.getEmpsByConditionIf(example);
        System.out.println("employeeList = " + employeeList);
    }

}
```

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