233 lines
6.7 KiB
Markdown
233 lines
6.7 KiB
Markdown
# 第八章：动态SQL
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基于MyBatis的客户管理系统的设计与开发
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## 1.复制第6章的代码
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导包：mybatis mysql
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准备数据
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数据库：mybatis 表 t_customer
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创建实体类Customer
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创建CustomerMapper.xml文件，写SQL语句的
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创建mybatis-config.xml文件，配置文件
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创建工具类，对外提供
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测试
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在上一章节中有所展示记录
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## 2.系统功能
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### 1. if 元素
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如果姓名和职业都不为空，按姓名和职业查找客户
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如果姓名不为空职业为空，按姓名查找客户
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如果姓名为空职业不为空，按职业查找客户
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如果姓名和职业都为空，则查找所有客户。
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#### 下面是 CustomerMapper.xml 文件中的 sql 语句：
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```java
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<!--
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1.如果姓名和职业都不为空，按姓名和职业查找客户
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select * from t_customer where 1=1 and username like concat('%',#{username},'%') and jobs=#{jobs}
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2.如果姓名不为空职业为空，按姓名查找客户
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select * from t_customer where 1=1 and username like concat('%',#{username},'%')
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3.如果姓名为空职业不为空，按职业查找客户
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select * from t_customer where 1=1 and jobs=#{jobs}
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4.如果姓名和职业都为空，则查找所有客户。
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select * from t_customer where 1=1
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-->
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test="username!=null and username!=''"
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此处的username是实体类Customer的成员变量,如果test中条件成立，and这一行代码就会被拼接到1=1的后面，否则，就不拼接
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and username like concat('%',#{username},'%')
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此处的第一个username是字段名，第2个username.是实体类Customer的成员变量 concat函数 连接字符串
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```
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```java
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<select id="findCustomerByNameAndJobs" parameterType="com.gzh.po.Customer" resultType="com.gzh.po.Customer">
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select * from t_customer where 1=1
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<if test="username!=null and username!=''">
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and username like concat('%',#{username},'%')
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</if>
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<if test="jobs!=null and jobs!=''">
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and jobs=#{jobs}
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</if>
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</select>
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```
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#### 测试类，通过名字进行查询：
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```java
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@Test
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public void findCustomerByNameAndJobsTest(){
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Customer customer = new Customer();
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customer.setUsername("w");
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List<Customer> objects = sqlSession.selectList("CustomerMapper.findCustomerByNameAndJobs", customer);
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for (Customer object: objects) {
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System.out.println(object);
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}
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}
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```
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#### 运行截图：
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传一个名字，按名字查询：
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不传参查询全部：
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### 2. choose - when - otherwise 元素
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当客户名不为空，只根据客户名查询
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当客户名为空，职业不为空，则只根据职业查询
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当客户名和职业都为空，则查询电话不为空的客户
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#### 下面是 CustomerMapper.xml 文件中的 sql 语句：
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```java
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<!--
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2.当客户名不为空，只根据客户名查询
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select * from t_customer where 1=1 and username like concat('%',#{username},'%')
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当客户名为空，职业不为空，则只根据职业查询
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select * from t_customer where 1=1 and jobs=#{jobs}
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当客户名和职业都为空，则查询电话不为空的客户
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select * from t_customer where 1=1 and phone is not null
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-->
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```
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```java
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<select id="findCustomerByNameOrJobs" parameterType="com.gzh.po.Customer" resultType="com.gzh.po.Customer">
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select * from t_customer where 1=1
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<choose>
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<when test="username!=null and username!=''">
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and username like concat('%',#{username},'%')
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</when>
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<when test="jobs!=null and jobs!=''">
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and jobs=#{jobs}
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</when>
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<otherwise>
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and phone is not null
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</otherwise>
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</choose>
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</select>
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```
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#### 测试类，通过职业进行查询：
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```java
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@Test
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public void findCustomerByNameOrJobs(){
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Customer customer = new Customer();
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customer.setJobs("teacher");
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List<Customer> objects = sqlSession.selectList("CustomerMapper.findCustomerByNameOrJobs", customer);
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for (Customer object: objects) {
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System.out.println(object);
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}
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}
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```
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#### 运行截图：
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传职业，按职业查询：
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不传参，查询有手机号：
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### 3. where 元素
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> 根据需要自动添加 where ，而且会自动保留或去掉 and 关键字
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如果姓名和职业都不为空，按姓名和职业查找客户
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如果姓名不为空职业为空，按姓名查找客户
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如果姓名为空职业不为空，按职业查找客户
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如果姓名和职业都为空，则查找所有客户。
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#### 下面是 CustomerMapper.xml 文件中的 sql 语句：
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```java
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<select id="findCustomerByNameAndJobs1" parameterType="com.gzh.po.Customer" resultType="com.gzh.po.Customer">
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select * from t_customer
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<where>
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<if test="username!=null and username!=''">
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and username like concat('%',#{username},'%')
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</if>
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<if test="jobs!=null and jobs!=''">
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and jobs=#{jobs}
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</if>
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</where>
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</select>
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```
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#### 测试类，通过姓名进行查询：
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```java
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@Test
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public void findCustomerByNameAndJobs1Test(){
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Customer customer = new Customer();
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customer.setUsername("j");
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List<Customer> objects = sqlSession.selectList("CustomerMapper.findCustomerByNameAndJobs1", customer);
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for (Customer object: objects) {
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System.out.println(object);
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}
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}
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```
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#### 运行截图：
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传一个名字，按名字查询：
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不传参查询全部：
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### 4. set 元素
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> 根据id更新客户信息 set元素根据需要自动去掉多余的逗号
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通过 ID 更新信息
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#### 下面是 CustomerMapper.xml 文件中的 sql 语句：
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```java
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<select id="updateCustomer" parameterType="com.gzh.po.Customer"> update t_customer
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<set>
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<if test="username!=null and username!=''">
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username=#{username},
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</if>
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<if test="jobs!=null and jobs!=''">
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jobs=#{jobs},
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</if>
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<if test="phone!=null and phone!=''">
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phone=#{phone},
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</if>
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</set>
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where id=#{id}
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</select>
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```
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测试类，通过 ID 进行修改：
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```java
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@Test
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public void updateCustomer(){
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Customer customer = new Customer();
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customer.setId(3);
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customer.setUsername("maliu");
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sqlSession.selectList("CustomerMapper.updateCustomer", customer);
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sqlSession.commit();
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sqlSession.close();
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}
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```
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运行截图：
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