MybatisMyBatis之动态SQL

Posted H__D

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了MybatisMyBatis之动态SQL相关的知识,希望对你有一定的参考价值。

  MyBatis 的强大特性之一便是它的动态 SQL,本章介绍动态 SQL

  查看本章,请先阅读【Mybatis】MyBatis对表执行CRUD操作(三)

  本例表结构

1 CREATE TABLE `employee` (
2   `id` int(11) NOT NULL AUTO_INCREMENT,
3   `last_name` varchar(255) DEFAULT NULL,
4   `gender` char(1) DEFAULT NULL,
5   `email` varchar(255) DEFAULT NULL
6   PRIMARY KEY (`id`)
7 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

 

if

  if标签:用于逻辑判断,其中test属性,填写的是判断表达式(OGNL)

  示例

  1、EmployeeMapper新增Sql如下:

 1 <!-- if:判断 -->
 2 <select id="testConditionIf"
 3     resultType="com.hd.test.pojo.Employee">
 4     select id, last_name lastName, gender from employee
 5     <!-- 
 6         test:判断表达式(OGNL) OGNL参照PPT或者官方文档。 
 7         c:if test 从参数中取值进行判断 遇见特殊符号应该去写转义字符: &&:
 8         
 9      -->
10     where 1 = 1
11     <if test="id != null">
12         AND id = #{id}
13     </if>
14     <!-- 表达式中,字符串使用\'\'单引号引起来 -->
15     <if test="lastName != null and lastName.trim() != \'\'">
16         AND last_name = #{lastName}
17     </if>
18     <!-- ognl会进行字符串与数字的转换判断  "0"==0 -->
19     <if test="gender==0 or gender==1">
20         AND gender = #{gender}
21     </if>
22     <!-- 转义字符: &amp;&amp; == &&    &quot;&quot; == ""-->
23     <if test="email != null &amp;&amp; lastName!=&quot;&quot;">
24         AND email = #{email}
25     </if>
26 </select>

   2、EmployeeMapper接口中,新增方法

1 public List<Employee> testConditionIf(Employee employee);

  3、测试方法

 1 @Test
 2 public void test001() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         List<Employee> list = mapper.testConditionIf(new Employee(null, "0", null));
12         System.out.println(list.size());
13         for (Employee employee : list) {
14             System.out.println(list);
15         }
16     } catch (Exception e) {
17         e.printStackTrace();  
18     } finally {
19         session.close();
20     }
21 }

  4、执行结果

    

 

choose

  有时我们不想应用到所有的条件语句,而只想从中择其一项。针对这种情况,MyBatis 提供了 choose 元素,它有点像 Java 中的 switch 语句。

  示例

  1、EmployeeMapper新增Sql如下:

 1 <!-- choose -->
 2 <select id="testConditionChoose" resultType="com.hd.test.pojo.Employee">
 3     select id, last_name lastName, gender from employee
 4     where 1 = 1
 5     <choose>
 6         <when test="id != null">
 7             AND id = #{id}
 8         </when>
 9         <when test="lastName != null">
10             AND last_name = #{lastName}
11         </when>
12         <when test="gender != null">
13             AND gender = #{gender}
14         </when>
15         <when test="email != null">
16             AND email = #{email}
17         </when>
18         <otherwise>
19             AND 1 = 1
20         </otherwise>
21     </choose>
22 </select>

  2、EmployeeMapper接口中,新增方法

1 public List<Employee> testConditionChoose(Employee employee);

   3、测试方法  

 1 @Test
 2 public void test002() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         List<Employee> list = mapper.testConditionChoose(new Employee(1, null, null, null));
12         System.out.println(list.size());
13         for (Employee employee : list) {
14             System.out.println(list);
15         }
16     } catch (Exception e) {
17         e.printStackTrace();  
18     } finally {
19         session.close();
20     }
21 }

  4、执行结果

    

where

  where标签:用于编写带where条件的sql,配合if标签使用,它会自动去除首个AND前缀。

  示例

  1、EmployeeMapper新增Sql如下:

 1 <!-- if + where -->
 2 <select id="testConditionIfWhere"
 3     resultType="com.hd.test.pojo.Employee">
 4     select id, last_name lastName, gender from employee
 5     <where>
 6         <if test="id != null">
 7             AND id = #{id}
 8         </if>
 9         <if test="lastName != null and lastName.trim() != \'\'">
10             AND last_name = #{lastName}
11         </if>
12         <if test="gender==0 or gender==1">
13             AND gender = #{gender}
14         </if>
15         <if test="email != null &amp;&amp; lastName!=&quot;&quot;">
16             AND email = #{email}
17         </if>
18     </where>
19 </select>

  2、EmployeeMapper接口中,新增方法

1 public List<Employee> testConditionIfWhere(Employee employee);

  3、测试方法

 1 @Test
 2 public void test003() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         List<Employee> list = mapper.testConditionIfWhere(new Employee("小红", "1", null));
12         System.out.println(list.size());
13         for (Employee employee : list) {
14             System.out.println(list);
15         }
16     } catch (Exception e) {
17         e.printStackTrace();  
18     } finally {
19         session.close();
20     }
21 }

  4、执行结果

    

trim

  trim标签:可以去掉字符串的首尾字符串,以及在字符串前后添加前后缀

  示例

  1、EmployeeMapper新增Sql如下:

 1 <select id="testConditionIfTrim" resultType="com.hd.test.pojo.Employee">
 2     select id, last_name lastName, gender from employee
 3     <!-- 后面多出的and或者or where标签不能解决 
 4         prefix="":前缀:trim标签体中是整个字符串拼串 后的结果。 prefix给拼串后的整个字符串加一个前缀 
 5         prefixOverrides="": 前缀覆盖: 去掉整个字符串前面多余的字符 
 6         suffix="":后缀 suffix给拼串后的整个字符串加一个后缀 
 7         suffixOverrides="" 后缀覆盖:去掉整个字符串后面多余的字符 -->
 8     <trim prefix="where" prefixOverrides="AND">
 9         <if test="id != null">
10             AND id = #{id}
11         </if>
12         <if test="lastName != null">
13             AND last_name = #{lastName}
14         </if>
15         <if test="gender != null">
16             AND gender = #{gender}
17         </if>
18         <if test="email != null">
19             AND email = #{email}
20         </if>
21     </trim>
22 </select> 

  2、EmployeeMapper接口中,新增方法

1 public List<Employee> testConditionIfTrim(Employee employee); 

  3、测试方法

 1 @Test
 2 public void test004() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         List<Employee> list = mapper.testConditionIfTrim(new Employee(1, null, null, null));
12         System.out.println(list.size());
13         for (Employee employee : list) {
14             System.out.println(list);
15         }
16     } catch (Exception e) {
17         e.printStackTrace();  
18     } finally {
19         session.close();
20     }
21 }

  4、执行结果

    

    

foreach

  动态 SQL 的另外一个常用的操作需求是对一个集合进行遍历,通常是在构建 IN 条件语句的时候

  示例

  1、EmployeeMapper新增Sql如下: 

 1 <!-- foreach -->
 2 <select id="testConditionForeach" resultType="com.hd.test.pojo.Employee">
 3     select id, last_name lastName, gender from employee
 4     <!--
 5          collection:指定要遍历的集合:
 6              list类型的参数会特殊处理封装在map中,map的key就叫list
 7          item:将当前遍历出的元素赋值给指定的变量
 8          separator:每个元素之间的分隔符
 9          open:遍历出所有结果拼接一个开始的字符
10          close:遍历出所有结果拼接一个结束的字符
11          index:索引。遍历list的时候是index就是索引,item就是当前值
12                        遍历map的时候index表示的就是map的key,item就是map的值
13          
14          #{变量名}就能取出变量的值也就是当前遍历出的元素
15        -->
16     <foreach collection="ids" item="id" separator="," open="where id in (" close=")" >
17         #{id}
18     </foreach>
19 </select>

  2、EmployeeMapper接口中,新增方法

1 public List<Employee> testConditionForeach(@Param("ids")List<Integer> ids);

  3、测试方法

 1 @Test
 2 public void test005() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         List<Employee> list = mapper.testConditionForeach(Arrays.asList(1, 2, 3, 4));
12         System.out.println(list.size());
13         for (Employee employee : list) {
14             System.out.println(list);
15         }
16     } catch (Exception e) {
17         e.printStackTrace();  
18     } finally {
19         session.close();
20     }
21

   4、执行结果

    

 

set

  set 元素会动态前置 SET 关键字,同时也会删掉无关的逗号,因为用了条件语句之后很可能就会在生成的 SQL 语句的后面留下这些逗号

  示例

  1、EmployeeMapper新增Sql如下: 

 1 <!-- set -->
 2 <update id="testConditionSet">
 3     update employee 
 4     <set>
 5         <if test="lastName != null">
 6             last_name = #{lastName},
 7         </if>
 8         <if test="gender != null">
 9             gender = #{gender},
10         </if>
11         <if test="email != null">
12             email = #{email},
13         </if>
14     </set>
15     where id = #{id}
16 </update> 

  2、EmployeeMapper接口中,新增方法

1 public boolean testConditionSet(Employee employee);

  3、测试方法 

 1 @Test
 2 public void test006() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         boolean f = mapper.testConditionSet(new Employee(1, "小白", "1", null));
12         System.out.println(f);
13         session.commit();
14     } catch (Exception e) {
15         e.printStackTrace();  
16     } finally {
17         session.close();
18     }
19 }

  4、执行结果

    

 

bind

  bind 元素可以从 OGNL 表达式中创建一个变量并将其绑定到上下文。比如:

1 <select id="testConditionBind" resultType="Blog">
2     <bind name="pattern" value="\'%\' + keyword + \'%\'" />
3     SELECT * FROM employee  WHERE last_name LIKE #{pattern}
4 </select>

 

 

sql

  可以用来包含其他sql

1 <sql id="selectSql">select id, last_name lastName, gender from employee</sql>
2     
3 <select id="testConditionInclude" resultType="com.hd.test.pojo.Employee">
4     <include refid="selectSql"></include>
5     where id = 1
6 </select>

 

 

 Mybatis中2个内置参数 _parameter和_databaseId

  示例

  1、EmployeeMapper新增Sql如下:

 1 <!-- 两个内置参数:
 2      不只是方法传递过来的参数可以被用来判断,取值。。。
 3      mybatis默认还有两个内置参数:
 4      _parameter:代表整个参数
 5          单个参数:_parameter就是这个参数
 6          多个参数:参数会被封装为一个map;_parameter就是代表这个map
 7      
 8      _databaseId:
 9          如果配置了databaseIdProvider标签。 _databaseId就是代表当前数据库的别名mysql
10          如果没配置了databaseIdProvider标签。 _databaseId为null
11   -->
12 <select id="testInnerParameter" resultType="com.hd.test.pojo.Employee">
13     <if test="_databaseId == \'mysql\'">select * from ${_parameter}</if>
14     <if test="_databaseId != \'mysql\'">select * from ${_parameter} where 1 = 1</if>
15 </select>

  2、mybatis-config.xml中的配置

1 <databaseIdProvider type="DB_VENDOR">
2     <!-- 为不同的数据库厂商起别名 -->
3     <property name="MySQL" value="mysql"/>
4     <property name="Oracle" value="oracle"/>
5     <property name="SQL Server" value="sqlserver"/>
6 </databaseIdProvider>

   3、EmployeeMapper接口中,新增方法 

1 public List<Employee> testInnerParameter(String tableName);

  4、测试方法 

 1 @Test
 2 public void test007() throws IOException {
 3     
 4     InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
 5     SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 6     
 7     SqlSession session = sessionFactory.openSession();
 8     
 9     try {
10         EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
11         List<Employee> list = mapper.testInnerParameter("employee");
12         System.out.println(list.size());
13         for (Employee employee : list) {
14             System.out.println(employee);
15         }
16         
17     } catch (Exception e) {
18         e.printStackTrace();  
19     } finally {
20         session.close();
21     }
22 }

  5、执行结果,从执行结果可以看出,_parameter == employee 参数,_databaseId == mysql 数据库别名

    Mybatis -- 动态Sql概述动态Sql之<if>(包含<where>)动态Sql之<foreach>sql片段抽取

MyBatisMyBatis之配置讲解

MybatisMyBatis之Sql配置文件的使用

MyBatisMyBatis Order By 字段动态动态排序

MybatisMyBatis之配置自定义数据源

MyBatisMyBatis 核心配置综述之 ResultSetHandler