动态SQL
动态SQLMyBatis最强大的特性之一就是它的动态SQL功能。
如果您有任何JDBC或类似框架的经验,那么您就会理解有条件地将SQL字符串连接在一起是多么痛苦,确保不要忘记空格或在列列表末尾省略al逗号。
动态SQL处理起来可能非常痛苦,而使用动态SOL永远都不会是一件很麻烦的事情,MyBatis使用一种强大的动态SQL语言(可以在任何映射的SQL语句中使用)无疑改善了这种情况。
使用JSTL或任何类似的基于XML的文本处理器的人都应该熟悉动态SOL元素。
在以前的MyBatis版本中,有很多元素需要了解和理解。MyBatis 3在此基础上有了很大的改进,现在只有不到一半的元素。
一起工作。MyBatis使用了强大的基于OGNL的表达式来消除大多数其他元素
 
--->if
--->choose(when,otherwise)
--->trim(where,set)
--->foreach
 
 
此文章及以后不带结果的截图,影响整体文章的布局美感!!!
其他的一些可以简单看一下之前的博文!
 
首先来看看本次工程的目录吧:
MyBatis(4)动态SQL-LMLPHP

mybatis-config.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 resource="db.properties" ></properties>
     <environments default="development">
           <environment id="development">
                <transactionManager type="JDBC" />
                <dataSource type="POOLED">
                     <property name="driver" value="${jdbc.driver}" />
                     <property name="url" value="${jdbc.url}" />
                     <property name="username" value="${jdbc.username}" />
                     <property name="password" value="${jdbc.password}" />
                </dataSource>
           </environment>
     </environments>
     <mappers>
           <mapper resource="DynamicSQL.xml"/>
     </mappers>
</configuration>

 Employee.java(getter&setter&toString)

public class Employee {
     private int id;
     private String name;
     private String gender;
     private String email;
     private Department dept;
}

 现在基本的布局已经完成!!

1)if

A.在DynamicMapper.java接口中

//携带了哪个字段的查询条件就携带这个字段的值
     public List<Employee> getEmpByIf(Employee emp);
 在Dynamic'SQl.xml文件
 
<!-- if -->
 <!-- 查询员工,要求,携带了那个字段查询条件就带上那个字段的字段值 -->
 <!--      public List<Employee> getEmpByIf(Employee emp); -->
 <select id="getEmpByIf" resultType="com.MrChengs.bean.Employee">
     select * from test
     where
          <!-- test:判断表达式(OGNL) -->
          <!-- OGNL:apache官方文档有明确的解释说明 -->
          <!-- 从参数中取值进行判断不是数据库中取值 -->
          <!-- 特殊字符应该写转义字符 -->
     <if test="id!=null">
           id=#{id}
     </if>
     <if test="name!=null and name!=''">
           and name like #{name}
     </if>
     <if test="email!=null and email.trim()!=''">
           and email like #{email}
     </if>
 </select>
在这个文件的内容简要的进行说明一下:
 and name like #{name}
这里的红色的name是我们查询的name值,不是数据库中的name
#{name}是把我们手动输入的红色name传递过去,进行数据库的查询
 
 测试类:
 
public SqlSessionFactory getSqlSessionFactory() throws IOException{
           String resource = "mybatis-config.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);   
           return new SqlSessionFactoryBuilder().build(inputStream);
     }
     @Test
     public void test() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                //传入的红色name值进行数据库的查询
                Employee emp = new Employee(5, "%Mr%", "boy", "%1287%");
                List<Employee> emps = mapper.getEmpByIf(emp);
                System.out.println(emps);
           }finally{
                session.close();
           }
     }

 查询之后的显示代码

 
DEBUG 10-02 12:13:49,806 ==>  Preparing: select * from test where id=? and name like ? and email like ?   (BaseJdbcLogger.java:159)
DEBUG 10-02 12:13:49,843 ==> Parameters: 5(Integer), %Mr%(String), %1287%(String)  (BaseJdbcLogger.java:159)
DEBUG 10-02 12:13:49,873 <==      Total: 1  (BaseJdbcLogger.java:159)
[Employee [id=5, name=MrChengs, gender=boy, email=1287xxxxxx@xx.com, dept=null]]
 B.在查询的时候,如果某些时候某些条件没带可能导致sql拼装有问题
实例:
 
<select id="getEmpByIf" resultType="com.MrChengs.bean.Employee">
     select * from test
     where
          <!-- test:判断表达式(OGNL) -->
          <!-- OGNL:apache官方文档有明确的解释说明 -->
          <!-- 从参数中取值进行判断不是数据库中取值 -->
          <!-- 特殊字符应该写转义字符 -->
     <!--此时我们假设忘记把id传进来 -->
     <if test="name!=null and name!=''">
           and name like #{name}
     </if>
     <if test="email!=null and email.trim()!=''">
           and email like #{email}
     </if>
 </select>

 look:

show message:DEBUG 10-02 12:18:30,831 ==>  Preparing: select * from test where and name like ? and email like ? 
(BaseJdbcLogger.java:159)
 
solution ①:  where 1=1
<select id="getEmpByIf" resultType="com.MrChengs.bean.Employee">
     select * from test
    <!-- 加入固定的条件,怎么拼装都行 -->
     where 1=1
          <!-- test:判断表达式(OGNL) -->
          <!-- OGNL:apache官方文档有明确的解释说明 -->
          <!-- 从参数中取值进行判断不是数据库中取值 -->
          <!-- 特殊字符应该写转义字符 -->
     <if test="name!=null and name!=''">
           and name like #{name}
     </if>
     <if test="email!=null and email.trim()!=''">
           and email like #{email}
     </if>
 </select>
solution ②:使用<where></where>  只会去掉一个and  或者or
 <select id="getEmpByIf" resultType="com.MrChengs.bean.Employee">
     select * from test
     <where>
                <!-- test:判断表达式(OGNL) -->
                <!-- OGNL:apache官方文档有明确的解释说明 -->
                <!-- 从参数中取值进行判断不是数据库中取值 -->
                <!-- 特殊字符应该写转义字符 -->
          <if test="name!=null and name!=''">
                and name like #{name}
          </if>
          <if test="email!=null and email.trim()!=''">
                and email like #{email}
          </if>
     </where>
 </select>

 注意使用and

2.使用trim标签进行,字符串截取

先看一个案例的错误代码展示:
 
DynamicSQLMapper.java
     //测试Trim
     public List<Employee> getEmpByIfTrim(Employee emp);

 在DynamicSQL.xml

<!-- 测试Trim() -->
 <!-- public List<Employee> getEmpByIfTrim(Employee emp); -->
 <select id="getEmpByIfTrim" resultType="com.MrChengs.bean.Employee">
    select * from test
    where
     <if test="id!=null">
           id=#{id} and
     </if>
     <if test="name!=null and name!=''">
           name like #{name}    and
     </if>
     <if test="email!=null and email.trim()!=''">
           email like #{email}
     </if>
 </select>
假设我们此时传参为name属性一个
@Test
     public void testgetEmpByIfTrim() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                Employee emp = new Employee("%Mr%", null, null);
                List<Employee> emps = mapper.getEmpByIfTrim(emp);
                System.out.println(emps);
           }finally{
                session.close();
           }
     }

 拼串结果

DEBUG 10-02 13:31:59,995 ==>  Preparing: select * from test where id=? and name like ? and

开始使用trim标签:(一些用法都在注释中,请注意看注释)

 <!-- 测试Trim() -->
 <!-- public List<Employee> getEmpByIfTrim(Employee emp); -->
 <select id="getEmpByIfTrim" resultType="com.MrChengs.bean.Employee">
    select * from test
<!-- prefix:前缀, trim标签体中是整个字符串拼串后的结果 给拼串后的整体字符串加一个前缀--> <!-- prefixOverrides:前缀覆盖, 去点整个前缀前面多余的字符串 --> <!-- suffix:后缀, 给拼串后的整个字符串加一个后缀 --> <!-- suffixOverrides:后缀覆盖,去掉整个字符串后面多余的字符串 -->

<trim prefix="where" suffixOverrides="and"> <if test="name!=null and name!=''"> name like #{name} and </if> <if test="email!=null and email.trim()!=''"> email like #{email} and </if> <if test="gender!=null"> gender=#{gender} </if> </trim> </select>

 测试:

public void testgetEmpByIfTrim() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                Employee emp = new Employee("%Mr%", null, null);
                List<Employee> emps = mapper.getEmpByIfTrim(emp);
                System.out.println(emps);
           }finally{
                session.close();
           }
     }

 结果拼串:

DEBUG 10-02 13:43:25,216 ==>  Preparing: select * from test where name like ?   (BaseJdbcLogger.java:159)
DEBUG 10-02 13:43:25,266 ==> Parameters: %Mr%(String)  (BaseJdbcLogger.java:159)

 注意:在测试id的时候,不写则默认为零,博主自己测试的时候遇到的,所以把id的查询条件拿掉了!

 
 
3.choose分支选择
如果带了id使用id进行查询,带了name就是用name进行查询
只能使用一个进行查询
 
接口类的代码:
//测试choose
     public List<Employee> getEmpBychoose(Employee emp);

 DynamicSQL.xml:

<!-- choose -->
 <!-- 如果带了id使用id进行查询,带了name就是用name进行查询,只能使用一个进行查询 -->
 <!-- public List<Employee> getEmpBychoose(Employee emp); -->
 <select id="getEmpBychoose" resultType="com.MrChengs.bean.Employee">
     select * from test
     <where>
           <choose>
                <when test="name!=null">
                     name like #{name}
                </when>    
                <when test="email!=null">
                     email = #{email}
                </when>
                <when test="id!=null">
                     id=#{id}
                </when>    
                <otherwise>
                     d_id=1
                </otherwise>
           </choose>
     </where>
 </select>

 测试代码:

     //测试choose
     @Test
     public void testgetEmpBychoose() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                Employee emp = new Employee("%Mr%", null, null);
                emp.setId(5);
                List<Employee> emps = mapper.getEmpBychoose(emp);
                System.out.println(emps);
           }finally{
                session.close();
           }
     }

 结果:

DEBUG 10-02 14:07:35,311 ==>  Preparing: select * from test WHERE name like ?   (BaseJdbcLogger.java:159)
DEBUG 10-02 14:07:35,363 ==> Parameters: %Mr%(String)  (BaseJdbcLogger.java:159)

 此时我们不仅传入了name同时还传入了id,但是拼串之后是使用name进行查询的

3.更新

A.<set></set>版本
在接口中:
     //更新方法
     public void updataEmp(Employee emp);

 在DynamicSQl.xml文件:

<!-- update更新 -->
  <!-- 更新 -->
 <!-- public void updataEmp(Employee emp); -->
 <update id="updataEmp">
  update test
  <set>
  <if test="name!=null">name=#{name},</if>
  <if test="email!=null">  email=#{email},</if>
  <if test="gender!=null">gender=#{gender},</if>
  </set>
  where  id=#{id}
 </update>

 使用<set>标签,可以自动为我们解决存在的    ”,“   问题

 测试:
     //更新upddate
     @Test
     public void testgetEmpupdate() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                Employee emp = new Employee("MrChengsR", "gril", null);
                emp.setId(7);
                mapper.updataEmp(emp);
                System.out.println(emp);
                session.commit();
           }finally{
                session.close();
           }
     }

 此时修改数据成功

 
 
B.<trim><trim> version
仅仅是修改xml文件,其余的都不变
<update id="updataEmp">
       update test
           <trim prefix="set" suffixOverrides=",">
                <if test="name!=null">name=#{name},</if>
                <if test="email!=null">  email=#{email},</if>
                <if test="gender!=null">gender=#{gender},</if>
           </trim>
       where  id=#{id}
      </update>

4.foreach

 A)foreach:
DynamicSQLMapper.java
     //foreach
     public List<Employee> getEmpsByCollection(List<Integer> list);

 DynamicSQL.xml

     <!-- foreach: -->
      <!--      public List<Employee> getEmpsByCollection(Employee emp); -->
     <select id="getEmpsByCollection" resultType="com.MrChengs.bean.Employee" >
           select * from test where id in(
           <!-- collection:指定遍历的集合 -->
           <!-- list类型的参数会做特殊的处理封装在map中,map的key叫list -->
           <!-- item:将当前遍历出的元素赋值给指定的变量 -->
           <!-- #{变量名} 就能取出当前遍历的元素 -->
           <!-- separator:每个元素之间的分隔符    此时是in(a,b,c,d)这里面的   , -->
           <!-- open:遍历出所有结果拼接一个开始的字符 -->
           <!-- close:便利的所有结果拼出结尾 -->
           <!-- index:遍历list是索引,遍历map就是map的key -->
           <foreach collection="list" item="item_id" separator=",">
                #{item_id}
           </foreach>
           )
     </select>
测试类:
 
@Test
     public void testgetEmpForeach() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           
           SqlSession session = sessionFactory.openSession();
           
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                
                List<Employee> emps = mapper.getEmpsByCollection(Arrays.asList(5,7,8));
                for(Employee emp : emps){
                     System.out.println(emp);
                }
           }finally{
                session.close();
           }
     }

 得到结果:

DEBUG 10-02 19:16:01,838 ==>  Preparing: select * from test where id in( ? , ? , ? )   (BaseJdbcLogger.java:159)
DEBUG 10-02 19:16:01,887 ==> Parameters: 5(Integer), 7(Integer), 8(Integer)  (BaseJdbcLogger.java:159)
DEBUG 10-02 19:16:01,909 <==      Total: 3  (BaseJdbcLogger.java:159)
Employee [id=5, name=MrChengs, gender=boy, email=xxxxxxxx@qq.com, dept=null]
Employee [id=7, name=MrChengs, gender=gril, email=zhangsan@qq.com, dept=null]
Employee [id=8, name=MrChen, gender=gril, email=xxxxxx@xx.xxx, dept=null]

B.批量保存

方法1:
接口类中:
     //批量存取
     public void addEmps(@Param("emps")List<Employee> employee);

 xml文件:

     <!-- //批量存取-->
     <!--  public void addEmps(@Param("emps")Employee employee); -->
     <insert id="addEmps">
           insert into test(name,gender,email,d_id)
           values
           <foreach collection="emps" separator="," item="emp">
            <!-- 传参数之前是我们new的一个对象,传参数之后是插入数据库的数据 -->
           (#{emp.name},#{emp.gender},#{emp.email},#{emp.dept.id})
           </foreach>
     </insert>

 实现类:

//批量存取
     @Test
     public void testgetEmpaddEmps() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                List<Employee> employee = new ArrayList<Employee>();
                employee.add(new Employee("Ma", "gril", "Ma@Ma", new Department(1)));
                employee.add(new Employee("Mb", "boy", "Mb@Mb", new Department(2)));
                mapper.addEmps(employee);
                session.commit();
           }finally{
                session.close();
           }
     }
此时是成功插入数据
 
方法二:
<!-- 方法二 -->
     <!-- 需要加上 -->
     <!-- jdbc.url=jdbc:mysql://localhost:3306/mybatis?allowMultiQueries=true -->
     <insert id="addEmps">
           <foreach collection="emps" separator=";" item="emp">
           insert into test(name,gender,email,d_id)
           values
           (#{emp.name},#{emp.gender},#{emp.email},#{emp.dept.id})
           </foreach>
     
     </insert>

 其余不变可以进行测试

 
c.两个重要的参数
     <!-- 两个重要的参数 -->
     <!-- _parameter:代表整个参数,单个参数就是这个参数,多个参数就是封装成的map -->
     <!-- _databaseId:配置了databaseIdProvider标签,就是代表当前数据库的别名 -->
 
_databaseId:
mybatis-config.xml
<databaseIdProvider type="DB_VENDOR">
           <property name="MySQL" value="mysql"/>
           <property name="Oracle" value="oracle"/>
     </databaseIdProvider>

 接口类中

//测试两个属性
     public List<Employee> getEmpselect();

 DynamicMapper.xml

 
<!-- 两个重要的参数 -->
     <!-- _parameter:代表整个参数,单个参数就是这个参数,多个参数就是封装成的map -->
     <!-- _databaseId:配置了databaseIdProvider标签,就是代表当前数据库的别名 -->
     
     <!-- public Employee getEmpselect(int id); -->

    <!-- 修改if中的test条件即可实现不同数据库之间的查询 -->
     <select id="getEmpselect" resultType="com.MrChengs.bean.Employee" databaseId="mysql">
           <if test="_databaseId=='mysql'">
                select * from test
           </if>
           <if test="_databaseId=='oracle'">
                select * from test
           </if>
     </select>

 测试类:

     //两个重要的参数
     @Test
     public void testgetEmpselect() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                List<Employee> emps= mapper.getEmpselect();
                for(Employee emp : emps){
                     System.out.println();
                }
           }finally{
                session.close();
           }
     }
 此时可以成功查询数据!!
 
 
_parameter
在接口类中:把刚刚测试代码加上id
 
//测试两个属性
     public List<Employee> getEmpselect(int id);

 在xnl文件中:

<!-- public Employee getEmpselect(int id); -->
     <select id="getEmpselect" resultType="com.MrChengs.bean.Employee" databaseId="mysql">
           <if test="_databaseId=='mysql'">
                select * from test
                <if test="_parameter!=null">
                     where id=#{id}
                </if>
           </if>
           <if test="_databaseId=='oracle'">
                select * from test
           </if>
     </select>
 测试类:
@Test
     public void testgetEmpselect() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                List<Employee> emps= mapper.getEmpselect(5);
                System.out.println(emps);
           }finally{
                session.close();
           }
     }
此时的查询成功!!!
 
 
D.bind标签的使用
接口类中:
     //测试两个属性
     //public List<Employee> getEmpselect();
     //public List<Employee> getEmpselect(int id);
     public List<Employee> getEmpselect(Employee em);
xml文件:
<select id="getEmpselect" resultType="com.MrChengs.bean.Employee" databaseId="mysql">
           <!-- bind:可以将OGNL表达式的值绑定到一个变量中,方便引用这个变量的值 -->
           <!-- name :是我们指定的绑定参数-->
           <!-- value :指定参数的值 -->
           <bind name="_name" value="'%'+name+'%'"/>
           
           <if test="_databaseId=='mysql'">
                select * from test
                <if test="_parameter!=null">
                     where name like #{_name}
                </if>
           </if>
           <if test="_databaseId=='oracle'">
                select * from test
           </if>
     </select>

 测试类:

 
     @Test
     public void testgetEmpselect() throws IOException {
           SqlSessionFactory sessionFactory = getSqlSessionFactory();
           SqlSession session = sessionFactory.openSession();
           try{
                DynamicSQLMapper mapper = session.getMapper(DynamicSQLMapper.class);
                //List<Employee> emps= mapper.getEmpselect();
                //List<Employee> emps= mapper.getEmpselect(5);
                Employee emp = new Employee();
                emp.setName("M");
                List<Employee> emps= mapper.getEmpselect(emp);
                System.out.println(emps);
           }finally{
                session.close();
           }
     }

E.SQL标签

 
     <!-- <include refid=""></include> -->
     <!-- SQL:抽取可重用的sql字段,方便后面引用 -->
     <!-- include:就是引用外部标签 -->
     <!--
           1.sql抽取:经常要查询的列名,或者插入用的列名抽取出来方便引用
           2.include来引用已经抽取的sql
           3.include还可以自定义一些property,sql标签内部只能使用自定义的属性
                 include-property:取值正确方式  ${prop}
                 #{不可以使用这种方式}
      -->
     <sql id="">
           <!-- 同时这里面还可以使用   if进行判断 -->
           <if test=""></if>
     </sql>
 
 
 
 
 
 
 
 
 
 
10-03 23:46