if标签

接口(EmployeeMapper.java)

package com.fish.dao;

import java.util.List;

import com.fish.pojo.Employee;

public interface EmployeeMapper {
    /**
     * 动态sql if拼接
     * @Author ZFH
     * @Date 2019年7月29日
     */
    public List<Employee> selEmployeeByConationIf(Employee employee);
}

配置文件(EmployeeMapper.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">
<mapper namespace="com.fish.dao.EmployeeMapper">

    <select id="selEmployeeByConationIf" resultType="com.fish.pojo.Employee">
        select id, last_name lastName, email, gender from tbl_employee where
        <!--
            test:判断表达式(OGNL)
            OGNL参照官方文档
            test:
                从参数中取值判断
                对于特殊字符需要使用转义字符例如
                &&:&amp;&anm;或者and
                "":&quot;&quot 或者使用单引号
            OGNL会进行紫都城的转换判断 例如下面的gender是String类型 但是我可以直接写 gender==1
         -->
            <if test="id != null">
                id = #{id}
            </if>
            <if test="lastName != null and lastName !='' ">
                and last_name like  "%" #{lastName} "%"
            </if>
            <if test="email != null and email != '' ">
                and email = #{email}
            </if>
            <if test="gender == 0 or gender == 1">
                and gender = #{gender}
            </if>
    </select>
</mapper>

测试类

@org.junit.Test
public void test01() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    Employee employee = new Employee();
    employee.setId(1);
    employee.setLastName("2");
    List<Employee> selEmployeeByConationIf = mapper.selEmployeeByConationIf(employee);
    System.out.println(selEmployeeByConationIf);
    //关闭Session
    openSession.close();

}

运行结果

[Employee [id=1, lastName=222, email=ZFH_FISH@163.COM, gender=1]]

问题

有些同学可能发现问题了,如果id我不传只传lastName 那么mybatis进行sql拼接的时候会带上and,这样一来sql语句就会报错了,那么怎么解决呢,这里有两种方法,1:在动态sql之前的sql后面的where后面加上1=1 然后每一个条件都加上and,2:使用where标签

where标签

将上面的方法改造一下

接口(EmployeeMapper.xml)

<select id="selEmployeeByConationIf" resultType="com.fish.pojo.Employee">
    select id, last_name lastName, email, gender from tbl_employee 
    <where>
        <!--
            test:判断表达式(OGNL)
            OGNL参照官方文档
            test:
                从参数中取值判断
                对于特殊字符需要使用转义字符例如
                &&:&amp;&anm;或者and
                "":&quot;&quot 或者使用单引号
            OGNL会进行紫都城的转换判断 例如下面的gender是String类型 但是我可以直接写 gender==1
         -->
        <if test="id != null">
            id = #{id}
        </if>
        <if test="lastName != null and lastName !='' ">
            and last_name like  "%" #{lastName} "%"
        </if>
        <if test="email != null and email != '' ">
            and email = #{email}
        </if>
        <if test="gender == 0 or gender == 1">
            and gender = #{gender}
        </if>
    </where>
</select>

测试类

@org.junit.Test
public void test01() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    Employee employee = new Employee();
    //employee.setId(1);
    employee.setLastName("2");
    List<Employee> selEmployeeByConationIf = mapper.selEmployeeByConationIf(employee);
    System.out.println(selEmployeeByConationIf);
    //关闭Session
    openSession.close();

}

运行结果

[Employee [id=1, lastName=222, email=ZFH_FISH@163.COM, gender=1], Employee [id=2, lastName=2, email=2, gender=1], Employee [id=5, lastName=22, email=lisi@163.com, gender=0]]

完美解决,通过这个例子我们知道,where标签可以帮我们把第一个多余的and或or去掉

上面的问题虽然解决了,但是还有一个问题,如果我的and是现在每个条件的后面的例如这样

<if test="id != null">
            id = #{id} and
        </if>
        <if test="lastName != null and lastName !='' ">
            last_name like  "%" #{lastName} "%"
        </if>
        <if test="email != null and email != '' ">
            and email = #{email} and 
        </if>
        <if test="gender == 0 or gender == 1">
            gender = #{gender}
        </if>

那么sql又会报错了这时候怎么解决呢下面我们来介绍一下trim标签

trim(自定义字符串截取)

接口(EmployeeMapper.java)

/**
 * 动态sql trim
 * @Author ZFH
 * @Date 2019年7月29日
 */
public List<Employee> selEmployeeByConationTrim(Employee employee);

配置文件(EmployeeMapper.xml)

<select id="selEmployeeByConationTrim"
    resultType="com.fish.pojo.Employee">
    select id, last_name lastName, email, gender from tbl_employee
    <!-- trim:
        prefix="":为拼接完的sql加一个前缀
        prefixOverrides="":前缀覆盖,去掉整个字符串前面多余的字符串
        suffix="" :为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="id != null">
            id = #{id} and
        </if>
        <if test="lastName != null and lastName !='' ">
            last_name like "%" #{lastName} "%" and
        </if>
        <if test="email != null and email != '' ">
            and email = #{email} and
        </if>
        <if test="gender == 0 or gender == 1">
            gender = #{gender}
        </if>
    </trim>
</select>

测试类

@org.junit.Test
public void test02() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    Employee employee = new Employee();
    //employee.setId(1);
    employee.setLastName("2");
    List<Employee> selEmployeeByConationIf = mapper.selEmployeeByConationTrim(employee);
    System.out.println(selEmployeeByConationIf);
    //关闭Session
    openSession.close();

}

运行结果

[Employee [id=1, lastName=222, email=ZFH_FISH@163.COM, gender=1], Employee [id=2, lastName=2, email=2, gender=1], Employee [id=5, lastName=22, email=lisi@163.com, gender=0]]

再一次完美解决

choole分支选择

接口(EmployeeMapper.java)

/**
* 动态sql choose分支选择
* @Author ZFH
* @Date 2019年7月29日
*/
public List selEmployeeByConationChoose(Employee employee);

配置文件(EmployeeMapper.xml)

<select id="selEmployeeByConationChoose"
    resultType="com.fish.pojo.Employee">
    select id, last_name lastName, email, gender from tbl_employee
    <where>
        <choose>
            <when test="id != null and id != '' ">
                id = #{id}
            </when>
            <when test="lastName != null and lastName != '' ">
                and last_name = #{lastName}
            </when>
            <when test="email != null and email != '' ">
                and email = #{email}
            </when>
            <otherwise>
                and gender = 0
            </otherwise>
        </choose>
    </where>
</select>

测试类

@org.junit.Test
public void test03() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    Employee employee = new Employee();
    employee.setId(1);
    employee.setLastName("2");
    List<Employee> selEmployeeByConationIf = mapper.selEmployeeByConationChoose(employee);
    System.out.println(selEmployeeByConationIf);
    //关闭Session
    openSession.close();

}

运行结果

[Employee [id=1, lastName=222, email=ZFH_FISH@163.COM, gender=1]]

if与choose的区别

很多同学发现if与choose的效果一样,那为什么这两个都存在呢,其实这两个标签效果是不一样的,if标签是只要满足条件的都会拼接到sql上,而choose标签是只要有一个满足了条件,则只会拼接这一条,其他的都不执行了.

set(修改信息)

接口(EmployeeMapper.java)

public void selEmployeeByConationSet2(Employee employee);

配置文件(EmployeeMapper.xml)

<select id="selEmployeeByConationSet2"
    resultType="com.fish.pojo.Employee">
    update tbl_employee 
        <set>
            <if test="lastName != null">
                last_name = #{lastName},
            </if>
            <if test="email != null">
                email = #{email},
            </if>
            <if test="gender != null">
                gender = #{gender}
            </if>
        </set>
    where id = #{id}
</select>

测试类

@org.junit.Test
public void test04() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    Employee employee = new Employee();
    employee.setId(1);
    employee.setLastName("张三1");
    mapper.selEmployeeByConationSet2(employee);

    openSession.commit();
    //关闭Session
    openSession.close();

}

使用trim完成修改

配置文件(其他的都一样)

<select id="selEmployeeByConationSet"
    resultType="com.fish.pojo.Employee">
    update tbl_employee 
        <trim prefix="set" suffixOverrides=",">
            <if test="lastName != null">
                last_name = #{lastName},
            </if>
            <if test="email != null">
                email = #{email},
            </if>
            <if test="gender != null">
                gender = #{gender}
            </if>
        </trim>
    where id = #{id}
</select>

使用foreach遍历集合

接口(EmployeeMapper.java)

/**
 * 动态sql foreach
 * @Author ZFH
 * @Date 2019年7月29日
 */
public List<Employee> selEmployeeByConationForeach(List<Integer> ids);

配置文件(EmployeeMapper.xml)

<select id="selEmployeeByConationForeach"
    resultType="com.fish.pojo.Employee">
    select * from tbl_employee where id in 
    <!-- 
        collection:指定要遍历的集合,有三个取值分别是:array,list,collection分别对应了数组,集合,Map根据传入值的类型设置
        item:将当前遍历出的元素赋值给指定的变量
        separator:每个元素之间的分隔符
        open:拼接一个开始的字符串
        close:拼接一个结束的字符串
        index:索引.遍历list的时候index就是索引,item就是当前值
                  遍历map的时候,index是map的key,item是map的值
     -->
        <foreach collection="list" item="item_id" separator="," open="(" close=")" index="i">
            #{item_id}
        </foreach>
</select>

测试类

@org.junit.Test
public void test05() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    List<Integer> list = new ArrayList<Integer>();
    list.add(1);
    list.add(2);
    List<Employee> selEmployeeByConationForeach = mapper.selEmployeeByConationForeach(Arrays.asList(1,2,3));

    System.out.println(selEmployeeByConationForeach);

    //关闭Session
    openSession.close();

}

运行结果

[Employee [id=1, lastName=张三1, email=ZFH_FISH@163.COM, gender=1], Employee [id=2, lastName=2, email=2, gender=1]]

foreach批量保存

接口EmployeeMapper.java

/**
 * 动态sql foreach 批量添加
 * @Author ZFH
 * @Date 2019年7月29日
 */
public void addEmployee(@Param("emps") List<Employee> emps);

配置文件EmployeeMapper.xml

<insert id="addEmployee">
    insert into tbl_employee(last_name,email,gender,d_id) values 
    <foreach collection="emps" item="emp" separator=",">
        (#{emp.lastName},#{emp.email},#{emp.gender},#{emp.department.id})
    </foreach>
</insert>

测试类

@org.junit.Test
public void test06() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);

    List<Employee> list = new ArrayList<Employee>();
    Department department = new Department();
    department.setId(1);
    Department department2 = new Department();
    department2.setId(2);
    list.add(new Employee(null,"李四","zfh@163.com","1",department));
    list.add(new Employee(null,"李四2","zfh@163.com","0",department2));
    mapper.addEmployee(list);

    openSession.commit();
    //关闭Session
    openSession.close();

}

运行结果

mybatis内置参数

mybatis有两个内置参数:_parameter,_databaseId

_parameter:代表整个参数
- 单个参数: _parameter就是这个参数
- 多个参数: 参数会被封装为一个map: _parameter就是代表这个map
_databaseId:如果配置了databaseIdProvider标签.
- _databaseId就是代表当前数据库的别名,例如: oracle

bind标签

接口(EmployeeMapper.java)

/**
 * 使用bind标签
 */
public List<Employee> selEmpByNameBind(String lastName);

配置文件(EmployeeMapper.xml)

<select id="selEmpByNameBind" resultType="com.fish.pojo.Employee">
<bind name="_lastName" value="'%'+_parameter+'%'"/><!--这里取值用mybatis的内置参数取,用参数名取不到,不知道什么原因,有知道的小伙伴可以告知一下-->
    select * from tbl_employee 
        <where>
             last_name like #{_lastName}
        </where>
</select>

测试类

@org.junit.Test
public void test07() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    List<Employee> selEmpByNameBind = mapper.selEmpByNameBind("四");
    System.out.println(selEmpByNameBind);

    //关闭Session
    openSession.close();

}

sql标签(抽取可重用sql片段)

接口(EmployeeMapper.java)

/**
 * 使用sql标签
 */
public List<Employee> selEmpByNamesql(String lastName);

配置文件(EmployeeMapper.xml)

<!-- 
    抽取可重用的sql片段,方便后面引用
    1, sql抽取:京城将要查询的列名,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标签内部就能使用自定义的属性
        inclyde-property:取值的正确方式${prop},
			不能用#{prop}这种方式
	 -->
	<sql id="selColumn">
		id,last_name,gender,${email2}<!--这里我觉得并没有实际的意义,可能是我还没有理解到精髓吧,以后了解了回来更新-->
</sql>
<select id="selEmpByNamesql" resultType="com.fish.pojo.Employee">
<bind name="_lastName" value="'%'+_parameter+'%'"/>
    select 
        <include refid="selColumn">
            <property name="email2" value="email"/>
        </include>
    from tbl_employee 
        <where>
             last_name like "%" #{_lastName} ""
        </where>
</select>

测试类

@org.junit.Test
public void test08() throws IOException {
    //读取配置文件
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    //获取SqlSessionFactory
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    SqlSession openSession = sqlSessionFactory.openSession();
    //调用getMapper方法获取该接口的实现类
    EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    List<Employee> selEmpByNameBind = mapper.selEmpByNamesql("四");
    System.out.println(selEmpByNameBind);

    //关闭Session
    openSession.close();

}

来源：https://blog.csdn.net/zzzffhh/article/details/99546389

标签

mybatis动态sql

test

last

select

MyBatis

mapper

Mybatis九(动态sql)

if标签

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类

运行结果

问题

where标签

接口(EmployeeMapper.xml)

测试类

运行结果

trim(自定义字符串截取)

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类

运行结果

choole分支选择

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类

运行结果

if与choose的区别

set(修改信息)

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类

使用trim完成修改

配置文件(其他的都一样)

使用foreach遍历集合

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类

运行结果

foreach批量保存

接口EmployeeMapper.java

配置文件EmployeeMapper.xml

测试类

运行结果

mybatis内置参数

bind标签

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类

sql标签(抽取可重用sql片段)

接口(EmployeeMapper.java)

配置文件(EmployeeMapper.xml)

测试类