MyBatis <if>标签的使用

超、凢脫俗 2022-05-15 02:48 270阅读 0赞

**示例【根据学生姓名和班级信息查询】**

**创建t\_student表**

![70][]

**创建Student**

package com.po;
    public class Student {
    	private Integer sid;		//学号
    	private String sname;		//姓名
    	private String sex;			//性别
    	private String classes;		//班级
    	public Integer getSid() {
    		return sid;
    	}
    	public void setSid(Integer sid) {
    		this.sid = sid;
    	}
    	public String getSname() {
    		return sname;
    	}
    	public void setSname(String sname) {
    		this.sname = sname;
    	}
    	public String getSex() {
    		return sex;
    	}
    	public void setSex(String sex) {
    		this.sex = sex;
    	}
    	public String getClasses() {
    		return classes;
    	}
    	public void setClasses(String classes) {
    		this.classes = classes;
    	}
    	@Override
    	public String toString() {
    		return "Student [sid=" + sid + ", sname=" + sname + ", sex=" + sex + ", classes=" + classes + "]";
    	}	
    }

**创建StudentMapper.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.mapper.StudentMapper">
    	
    	<select id="getStudentByNameAndClasses" resultType="com.po.Student">
    		select * from t_student where 1=1
    		<if test="sname!=null">
    			and sname like concat('%',#{sname},'%')
    		</if>
    		<if test="classes!=null">
    			and classes=#{classes}
    		</if>
    	</select>
    </mapper>

**配置mybatis-config.xml并加StudentMapper.xml**

**创建StudentDao**

package com.dao;
    import java.util.ArrayList;
    import java.util.List;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.jupiter.api.Test;
    import com.factory.SessionFactory;
    import com.po.Student;
    public class StudentDao {
    	private SqlSession session=SessionFactory.getSqlSession();
    	private List<Student> students=new ArrayList<Student>();
    	@Test
    	public void getStudentByNameAndClasses(){
    		Student stu=new Student();
    		stu.setSname("张三");
    		stu.setClasses("大一");
    		students=session.selectList("com.mapper.StudentMapper.getStudentByNameAndClasses", stu);
    		for (Student student : students) {
    			System.out.println(student);
    		}
    	}
    }

**传递sname、classes两个参数，然后执行getStudentByNameAndClasses()方法**

![70 1][]

**只传递classses参数，然后执行getStudentByNameAndClasses()方法**

![70 2][]

[70]: /images/20220515/f3683ede67454b78ace06587d9901c43.png
[70 1]: /images/20220515/6a70c1dc52034b4b893026c67ca8c825.png
[70 2]: /images/20220515/14f731f017b746129e930cd0b430a741.png