9SpringBoot+Mybatis整合------动态sql

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开发工具:STS

前言:

mybatis框架中最具特色的便是sql语句中的自定义,而动态sql的使用又使整个框架更加灵活。

动态sql中的语法:

where标签

if标签

trim标签

set标签

switch\\when标签

foreach标签


一、搭建项目

1.创建用户表:

    

 

2.添加实体:   

 1 package com.xm.pojo;
 2 /**
 3  * 用户实体
 4  * @author xm
 5  *
 6  */
 7 public class User {
 8     
 9     private int id;
10     private String name;
11     private String username;
12     private int age;
13     private String phone;
14     private String email;
15     //无参构造函数必须有,ORM框架调用的就是无参构造函数
16     public User() {
17         
18     }
19     public User(int id, String name, String username, int age, String phone, String email) {
20         super();
21         this.id = id;
22         this.name = name;
23         this.username = username;
24         this.age = age;
25         this.phone = phone;
26         this.email = email;
27     }
28     public int getId() {
29         return id;
30     }
31     public void setId(int id) {
32         this.id = id;
33     }
34     public String getName() {
35         return name;
36     }
37     public void setName(String name) {
38         this.name = name;
39     }
40     public String getUsername() {
41         return username;
42     }
43     public void setUsername(String username) {
44         this.username = username;
45     }
46     public int getAge() {
47         return age;
48     }
49     public void setAge(int age) {
50         this.age = age;
51     }
52     public String getPhone() {
53         return phone;
54     }
55     public void setPhone(String phone) {
56         this.phone = phone;
57     }
58     public String getEmail() {
59         return email;
60     }
61     public void setEmail(String email) {
62         this.email = email;
63     }
64     
65     @Override
66     public String toString() {
67         return "User [id=" + id + ", name=" + name + ", username=" + username + ", age=" + age + ", phone=" + phone
68                 + ", email=" + email + "]";
69     }
70     
71     
72     
73     
74 
75 }
User.java

3.添加mapper接口:

 1 package com.xm.mapper;
 2 
 3 /**
 4  * 用户mapper接口
 5  * @author xm
 6  *
 7  */
 8 public interface UserMapper {
 9 
10 }
UserMapper.java

4.添加mapper映射:

1 <?xml version="1.0" encoding="UTF-8" ?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
3 <!--用户mapper关系映射  -->
4 <mapper namespace="com.xm.mapper.UserMapper">
5 
6 </mapper>
UserMapper.xml

5.添加测试类:

 1 package com.xm;
 2 
 3 
 4 import org.junit.runner.RunWith;
 5 import org.springframework.beans.factory.annotation.Autowired;
 6 import org.springframework.boot.test.context.SpringBootTest;
 7 import org.springframework.test.context.junit4.SpringRunner;
 8 
 9 import com.xm.mapper.UserMapper;
10 
11 @RunWith(SpringRunner.class)
12 @SpringBootTest
13 public class UserTest {
14     
15     @Autowired
16     private UserMapper userMapper;
17     
18 
19 }
UserText.java

 

二、动态sql

1.if标签的使用 

(1)添加mapper接口:

1 /**
2      * 根据条件查出学生
3      * @param user
4      * @return
5      */
6     public List<User> getUser(User user);

 

(2)添加mapper映射:

1 <select id="getUser" resultType="user">
2 select * from user where 1=1
3 <if test="id != null">and id=#{id} </if>
4 <if test="age != null">and age=#{age} </if>
5 <if test="name != null">and name=#{name}</if>
6 </select>

(3)添加测试:

 1 @Autowired
 2     private UserMapper userMapper;
 3     
 4     @Test
 5     public void getUserTest() {
 6         User user = new User(null , "小明" , null , 12 , null , null);
 7         List<User> users = userMapper.getUser(user);
 8         System.out.println(users);
 9 
10     }

(4)测试结果:

(5)思考:

where 1=1 在这里的作用是什么呢?可以不用它吗?

2.where标签的使用

(1)更改mapper映射:

1 <select id="getUser" resultType="user">
2 select * from user 
3 <where>
4 <if test="id != null">and id=#{id} </if>
5 <if test="age != null">and age=#{age} </if>
6 <if test="name != null">and name=#{name}</if>
7 </where>
8 </select>

(2)测试结果:

(3)思考:

and id=#{id} 换成 id=#{id} and 会怎样?

3.trim标签的使用

(1)更改mapper映射:

1 <select id="getUser" resultType="user">
2 select * from user 
3 <trim prefix="where" suffixOverrides="and">
4 <if test="id != null">id=#{id} and</if>
5 <if test="age != null">age=#{age} and</if>
6 <if test="name != null">name=#{name} and</if>
7 </trim>
8 </select>

 

(2)测试结果:

(3)分析:

trim标签下的四个属性:

prefix:在标签开始添加上该字符串

suffixOverrides:在标签末尾去除上该字符串

suffix:在标签末尾添加上该字符串

prefixOverrides:在标签开始去除上该字符串

4.set标签的使用

(1)描述需求:

用在update语句中,如果字段参数不为null,则修改此参数

(2)添加mapper接口:

1 /**
2      * 根据id修改所有非空字段
3      * @param user
4      */
5     public void updateUserById(User user);

 

(3)添加mapper映射:

 1 <update id="updateUserById">
 2 update user
 3 <set>
 4 <if test="name != null">name=#{name},</if>
 5 <if test="age != null">age=#{age},</if>
 6 <if test="username != null">username=#{username},</if>
 7 <if test="email != null">email=#{email},</if>
 8 <if test="phone != null">phone=#{phone}</if>
 9 </set>
10 <where>
11 id=#{id}
12 </where>
13 </update>

 

(4)添加测试方法:

1 @Test
2     public void updateUserTest() {
3         
4         User user = new User(1, null, null, null, "12545564454", "14548445@qq.com");
5         userMapper.updateUserById(user);
6         
7     }

 

(5)测试结果

 

5.switch\\when标签的使用

(1)描述需求:

满足id!=null查询id,

否则,看满足age否,

接着,看name是否满足,

最后,按age>10查询

(2)更改mapper映射:

1 <select id="getUser" resultType="user">
2 select * from user where
3 <choose>
4 <when test="id != null">id=#{id} </when>
5 <when test="age != null">age=#{age}</when>
6 <when test="name != null">name=#{name} </when>
7 <otherwise>age>10</otherwise>
8 </choose>
9 </select>

 

(3)测试结果:

 

6.foreach标签的使用

 (1)需求描述:

查出多个id的user

(2)添加mapper接口:

1     /**
2      * 根据id批量查询
3      * @param ids
4      * @return
5      */
6     public List<User> listById(List<Integer> ids);

 

(3)添加mapper映射:

1 <select id="listById" resultType="user" parameterType="list">
2 select * from user where id in
3 <foreach collection="list" item="id" separator=","  open="("  close=")">
4 #{id}
5 </foreach>
6 </select>

 

(4)添加测试用例:

1 @Test
2     public void listTest() {
3         
4         List<User> users = userMapper.listById(Arrays.asList(1));
5         System.out.println(users);
6         
7     }

(5)分析:

foreach标签下的所有属性:

collection:获取的集合名,如果是list集合,springboot会把它的key值默认封装为list

item:遍历的单个属性值

separator:拼接隔离的字符串

open:在循环的开始拼接的字符串

close:在循环的结束拼接的字符串

index:索引,在map中作为key


 

                                                                                2018-07-04

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