目录/Contents
第3章 动态SQL
学习目标
掌握MyBatis中动态SQL元素的使用
掌握MyBatis的条件查询操作
掌握MyBatis的更新操作
掌握MyBatis的复杂查询操作
学习内容
1 动态SQL中的元素
1.1 使用动态SQL的好处
1.2 动态SQL常用元素
2 条件查询操作
2.1 <if>元素
<!– 该xml文件中只列出了if元素的动态SQL-->
<if test="username !=null and username !=‘’“>
and username like concat('%',#{username}, '%')
</if>
<if test="jobs !=null and jobs !=‘’“>
and jobs= #{jobs}
</if>
2.2 <choose>、<when>、<otherwise>元素
<!-- 只展示三个组合元素的部分-->
<choose>
<when test="username !=null and username !=''">
and username like concat('%',#{username}, '%')
</when>
<when test="jobs !=null and jobs !=''">
and jobs= #{jobs}
</when>
<otherwise>and phone is not null</otherwise>
</choose>
2.3 <where>、<trim>元素
<select id="findCustomerByNameAndJobs"
parameterType="com.itheima.pojo.Customer"
resultType="com.itheima.pojo.Customer">
select * from t_customer
<where>
<if test="username !=null and username !=''">
and username like concat('%',#{username}, '%')</if>
<if test="jobs !=null and jobs !=''">
and jobs= #{jobs}</if>
</where></select>
<select id="findCustomerByNameAndJobs"
parameterType="com.itheima.pojo.Customer"
resultType="com.itheima.pojo.Customer">
select * from t_customer
<trim prefix="where" prefixOverrides="and" >
<if test="username !=null and username !=''">
and username like concat('%',#{username}, '%')</if>
<if test="jobs !=null and jobs !=''">
and jobs= #{jobs}</if></trim>
</select>
3 更新操作
3.1 <set>元素
<update id="updateCustomerBySet" parameterType="com.itheima.pojo.Customer">update t_customer
<set>
<if test="username !=null and username !=''">
username=#{username},</if>
<if test="jobs !=null and jobs !=''"> jobs=#{jobs},</if>
<if test="phone !=null and phone !=''">phone=#{phone},</if>
</set> where id=#{id}
</update>
4 复杂查询操作
4.1 <foreach>元素的属性
4.2 <collection>属性的取值
4.3 <foreach>元素迭代数组
<select id="findByArray" parameterType="java.util.Arrays"
resultType="com.itheima.pojo.Customer">select * from t_customer where id in
<foreach item="id" index="index" collection="array"
open="(" separator="," close=")"> #{id}
</foreach>
select>
public void findByArrayTest() {
SqlSession session = MyBatisUtils.getSession(); // 获取SqlSession
Integer[] roleIds = {2,3}; // 创建数组，封装查询id
// 执行SqlSession的查询方法，返回结果集
List<Customer> customers = session.selectList("com.itheima.mapper"
+ ".CustomerMapper.findByArray", roleIds);
for (Customer customer : customers) {System.out.println(customer);}
session.close();
}
4.4 <foreach>元素迭代List
<select id="findByList" parameterType="java.util.Arrays"
resultType="com.itheima.pojo.Customer">
select * from t_customer where id in
<foreach item="id" index="index" collection="list"
open="(" separator="," close=")">
#{id}
</foreach>
</select>
public void findByListTest() {
SqlSession session = MyBatisUtils.getSession();
List<Integer> ids=new ArrayList<Integer>();
ids.add(1); ids.add(2);
List<Customer> customers = session.selectList("com.itheima.mapper"
+ ".CustomerMapper.findByList", ids);
for (Customer customer : customers) {System.out.println(customer);
} session.close();
}
4.5 <foreach>元素迭代Map
下面通过一个案例演示如何使用元素迭代Map集合，实现多参数入参查询操作，案例具体实
现步骤如下。
在映射文件CustomerMapper.xml中，添加使用元素迭代Map集合执行批量查询操作的动态SQL。
select * from t_customer where jobs=#{jobs} and id in
#{roleMap}
在测试类MyBatisTest中，编写测试方法findByMapTest()，用于批量查询客户信息。
public void findByMapTest() {
SqlSession session = MyBatisUtils.getSession();
List ids=new ArrayList();
ids.add(1); ids.add(2); ids.add(3);
Map<String,Object> conditionMap = new HashMap<String, Object>();
conditionMap.put(“id",ids); conditionMap.put(“jobs”,“teacher”);
List customers = session.selectList(“com.itheima.mapper”
+ “.CustomerMapper.findByMap”, conditionMap);
for (Customer customer : customers) { System.out.println(customer);}
session.close();
}
执行MyBatisTest测试类的findByMapTest()方法，控制台会输出结果。
5 案例：学生信息查询系统
5.1 需求
5.2 项目搭建
5.3 数据准备
USE mybatis;
CREATE TABLE dm_student(
id int(32) PRIMARY KEY AUTO_INCREMENT,
name varchar(50),
major varchar(50),
sno varchar(16) );
# 插入7条数据，其他省略
INSERT INTO dm_student VALUES ('1', '张三', '数学', '10001');
5.4 POJO类准备
public class Student {// 定义变量主键id，姓名name，专业major，学号sno
private Integer id; private String name;
private String major;
private String sno;
// 省略getter/setter方法
@Override
public String toString() {
return “Student{” + “id=” + id + “, name=‘” + name + “, major=" + major + ", sno=" + sno + '}';}}
5.5 创建映射文件
<mapper namespace="com.itheima.mapper.StudentMapper">
<select id=“findStudentByNameAndMajor” parameterType=“com.itheima.pojo.Student” resultType="com.itheima.pojo.Student">
select * from dm_student where 1=1 <choose>
<when test="name !=null and name !=''">
and name like concat('%',#{name}, '%')</when>
<when test="major !=null and major !=''"> and major= #{major}</when>
<otherwise> and sno is not null</otherwise> </choose>
</select>
</mapper>
5.6 修改mybatis-config.xml核心配置文件
<mapper resource="com/itheima/mapper/StudentMapper.xml"/>
5.7 编写MyBatisUtils工具类
public class MyBatisUtils {
private static SqlSessionFactory sqlSessionFactory = null;
static {
try {
Reader reader = Resources.getResourceAsReader(“mybatis-config.xml”); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (Exception e) {e.printStackTrace();} }
public static SqlSession getSession() {
return sqlSessionFactory.openSession();}
}
5.8 编写测试方法
public void findStudentByNameOrMajorTest() {
SqlSession session=MyBatisUtils.getSession();
Student student=new Student();
student.setName("张三");
student.setMajor("英语");
List<Student> students = session.selectList("com.itheima.mapper"
+ ".StudentMapper.findStudentByNameAndMajor",student);
for (Student student2 : students) {System.out.println(student2);}
session.close();
}
5.9 查看运行结果
5.10 多条件查询案例结果分析
5.11 修改映射文件
<select id="findByList" parameterType="java.util.List"
resultType="com.itheima.pojo.Student">
select * from dm_student where id in
<foreach item="id" index="index" collection="list"
open="(" separator="," close=")">
#{id}
</foreach>
</select>
5.12 编写测试方法
public void findByListTest() {
SqlSession session = MyBatisUtils.getSession();
List<Integer> ids=new ArrayList<Integer>();
for(int i =1;i<5;i++){
ids.add(i);}
List<Student> students = session.selectList("com.itheima.mapper"
+ ".StudentMapper.findByList", ids);
for (Student student : students) { System.out.println(student);}
session.close();
}
