MyBatis學習筆記（四）—— 動態SQL
阿新 • • 發佈：2020-12-28
MyBatis學習筆記（四）—— 動態SQL
尚矽谷-MyBatis
https://www.bilibili.com/video/BV1d4411g7tv?p=230
文章目錄
一、if標籤
動態SQL：簡化SQL語句動態拼串操作。
（1）建表t_teacher
（2）新建Teacher實體類和dao
public class Teacher { private Integer id; private String name; private String course; private String address; private Date birth; public Teacher(Integer id, String name, String course, String address, Date birth) { this.id = id; this.name = name; this.course = course; this.address = address; this.birth = birth; } public Teacher() { } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getCourse() { return course; } public void setCourse(String course) { this.course = course; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public Date getBirth() { return birth; } public void setBirth(Date birth) { this.birth = birth; } @Override public String toString() { return "Teacher{" + "id=" + id + ", name='" + name + '\'' + ", course='" + course + '\'' + ", address='" + address + '\'' + ", birth=" + birth + '}'; } } public interface TeacherDao { public Teacher getTeacherById(Integer id); public List<Teacher> getTeacherByCondition(Teacher teacher); }
（3）編寫全域性配置檔案
dbconfig.properties：
driverclass=com.mysql.cj.jdbc.Driver
jdbcurl=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2B8&useSSL=false
username=root
password=rootmybatis.xml：
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <!--properties屬性：引用外部配置檔案 resource：從類路徑下開始引用 url：引用磁碟路徑或網路路徑下的資源 --> <properties resource="dbconfig.properties"/> <settings> <!--開啟延遲載入物件--> <setting name="lazyLoadingEnabled" value="true"/> <!--開啟屬性按需載入--> <setting name="aggressiveLazyLoading" value="false"/> </settings> <!--default預設使用的環境--> <environments default="development"> <!--id是當前環境的唯一標識--> <environment id="development"> <transactionManager type="JDBC"/> <!--配置連線池--> <dataSource type="POOLED"> <!--取出配置檔案中的值--> <property name="driver" value="${driverclass}"/> <property name="url" value="${jdbcurl}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <!--mappers（對映器）：寫好的sql對映檔案需要使用mappers註冊進來--> <mappers> <!--resource：在類路徑下找對映檔案 url：引用磁碟路徑或網路路徑下的對映檔案 class：直接引用介面的全類名，需要把xml和dao介面放在同目錄下切命名相同 --> <mapper resource="teacherdao.xml"/> </mappers> </configuration>
（4）編寫SQL配置檔案
teacherdao.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"> <!--namespace：名稱空間。寫介面給的全類名，相當於告訴MyBatis這個配置檔案是實現哪個介面的。--> <mapper namespace="smq.dao.TeacherDao"> <select id="getTeacherById" resultMap="teacherMap"> select * from t_teacher where id=#{id} </select> <select id="getTeacherByCondition" resultMap="teacherMap"> select * from t_teacher where <!--test中編寫判斷條件 id!=null表示取出傳入的javaBean屬性中的id值判斷其是否為空 --> <if test="id!=null && name!=''"> id > #{id} </if> <if test="name!=null"> and teacherName like #{name} </if> <if test="birth!=null"> and birth_name > #{birth} </if> </select> <resultMap id="teacherMap" type="smq.javabean.Teacher"> <id property="id" column="id"/> <result property="address" column="address"/> <result property="course" column="class_name"/> <result property="name" column="teacherName"/> <result property="birth" column="birth_date"/> </resultMap> </mapper>
（5）測試
public class MyBatisTest {
SqlSessionFactory sqlSessionFactory;
//@Test之前執行
@Before
public void initSqlSessionFactory() throws IOException {
//根據全域性配置檔案建立一個SqlSessionFactory
String resource = "mybatis.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
//SqlSessionFactory是SqlSession工廠，負責建立SqlSession物件
//SqlSession代表和資料庫的一次會話
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
/**
* @throws IOException
*/
@Test
public void testTeacher() throws IOException {
//initSqlSessionFactory();
//獲取和資料庫的一次會話
SqlSession openSession = sqlSessionFactory.openSession();
//使用SqlSession操作資料庫
//獲取dao介面的實現
try {
TeacherDao teacherDao = openSession.getMapper(TeacherDao.class);
Teacher teacher = teacherDao.getTeacherById(1);
System.out.println(teacher);
}finally {
openSession.close();
}
}
/**
* if測試
* @throws IOException
*/
@Test
public void testTeacherIf() throws IOException {
//initSqlSessionFactory();
//獲取和資料庫的一次會話
SqlSession openSession = sqlSessionFactory.openSession();
//使用SqlSession操作資料庫
//獲取dao介面的實現
try {
TeacherDao teacherDao = openSession.getMapper(TeacherDao.class);
Teacher teacher = new Teacher();
teacher.setId(1);
teacher.setName("%a%");
List<Teacher> teachers = teacherDao.getTeacherByCondition(teacher);
System.out.println(teachers);
}finally {
openSession.close();
}
}
}二、trim標籤
trim標籤：擷取字串。
- prefix：字首，為下面的sql整體新增一個字首。
- prefixOverrides：取出整體字串前多餘的字元。
- suffix：為整體新增一個字尾。
- suffixOverrides：取出整體字串後獲取的字尾。
<select id="getTeacherByCondition" resultMap="teacherMap">
select * from t_teacher where
<!--test中編寫判斷條件
id!=null表示取出傳入的javaBean屬性中的id值判斷其是否為空
-->
<!--擷取字串
prefix：字首，為下面的sql整體新增一個字首
prefixOverrides：取出整體字串前多餘的字元
suffix：為整體新增一個字尾
suffixOverrides：取出整體字串後獲取的字尾
-->
<trim prefix="where" prefixOverrides="and" suffix="" suffixOverrides="and">
<if test="id!=null && name!=''">
id > #{id} and
</if>
<if test="name!=null">
and teacherName like #{name} and
</if>
<if test="birth!=null">
and birth_name > #{birth} and
</if>
</trim>
</select>三、foreach標籤
foreach標籤：遍歷集合。
- collection="ids"：指定要遍歷集合的key。
- close=")" ：以)結束。
- index="i" ：索引。
- item="id_item"：每次遍歷出的元素的變數名，方便引用。
- open="(" ：以(結束。
- separator=","：每次遍歷元素的分隔符。
（1）TeacherDao新增方法
public List<Teacher> getTeacherByIdIn(@Param("ids") List<Integer> ids);
（2）teacherdao.xml
<select id="getTeacherByIdIn" resultMap="teacherMap">
select * from t_teacher where id in
<!--遍歷集合
collection="ids"：指定要遍歷集合的key
close=")" ：以)結束
index="i" ：索引
item="id_item"：每次遍歷出的元素的變數名，方便引用
open="(" ：以(結束
separator=","：每次遍歷元素的分隔符
-->
<foreach collection="ids" close=")" index="" item="id_item" open="(" separator=",">
#{id_item}
</foreach>
</select>（3）測試
/**
* foreach測試
* @throws IOException
*/
@Test
public void testTeacherForeach() throws IOException {
//initSqlSessionFactory();
//獲取和資料庫的一次會話
SqlSession openSession = sqlSessionFactory.openSession();
//使用SqlSession操作資料庫
//獲取dao介面的實現
try {
TeacherDao teacherDao = openSession.getMapper(TeacherDao.class);
List<Teacher> teachers = teacherDao.getTeacherByIdIn(Arrays.asList(1, 2, 3));
System.out.println(teachers);
}finally {
openSession.close();
}
}四、choose標籤
（1）TeacherDao新增方法
public List<Teacher> getTeacherByConditionChoose(Teacher teacher);
（2）teacherdao.xml
<select id="getTeacherByConditionChoose" resultMap="teacherMap">
select * from t_teacher
<where>
<choose>
<when test="id!=null">
id=#{id}
</when>
<when test="name!=null and !name.equals("")">
teacherName=#{name}
</when>
<when test="birth!=null">
birth_date=#{birth}
</when>
<otherwise>
1=1
</otherwise>
</choose>
</where>
</select>（3）測試
/**
* choose測試
* @throws IOException
*/
@Test
public void testTeacherChoose() throws IOException {
//initSqlSessionFactory();
//獲取和資料庫的一次會話
SqlSession openSession = sqlSessionFactory.openSession();
//使用SqlSession操作資料庫
//獲取dao介面的實現
try {
TeacherDao teacherDao = openSession.getMapper(TeacherDao.class);
Teacher teacher = new Teacher();
teacher.setId(1);
teacher.setName("admin");
List<Teacher> teachers = teacherDao.getTeacherByConditionChoose(teacher);
System.out.println(teachers);
}finally {
openSession.close();
}
}五、Set標籤
（1）TeacherDao新增方法
public int updateTeacher(Teacher teacher);
（2）teacherdao.xml
<update id="updateTeacher">
update t_teacher
<set>
<if test="name!=null and !name.equals("")">
teacherName=#{name},
</if>
<if test="course!=null and !course.equals("")">
class_name=#{course},
</if>
<if test="address!=null and !address.equals("")">
address=#{address},
</if>
<if test="birth!=null">
birth_date=#{birth},
</if>
</set>
<where>
id=#{id}
</where>
</update>（3）測試
注意：SqlSession openSession = sqlSessionFactory.openSession(true);！！！
/**
* set測試
* @throws IOException
*/
@Test
public void testTeacherSet() throws IOException {
//initSqlSessionFactory();
//獲取和資料庫的一次會話
SqlSession openSession = sqlSessionFactory.openSession(true);
//使用SqlSession操作資料庫
//獲取dao介面的實現
try {
TeacherDao teacherDao = openSession.getMapper(TeacherDao.class);
Teacher teacher = new Teacher();
teacher.setId(1);
teacher.setName("adminupdate");
Integer id = teacherDao.updateTeacher(teacher);
System.out.println("更新了" + id + "條資料");
}finally {
openSession.close();
}
}