MyBatis(三)-动态SQL

1、if

<if>动态标签：判断参数时满足test指定的条件，如果满足，就执行if（增加if标签中的SQL语句）;

注意：test里面使用的参数，可以是mybatis的默认参数，也可以是实体属性名，但是不能是没有指定别名的参数名(尤其是单个参数，也必须起别名，否则异常);

1.1 SQL

单独使用if，如果不满足条件会SQL拼接出问题，一般我门都跟where一起使用；

<!-- List<Anime> selectAnimesByConditionUserIf(@Param(\"cid\") Integer cid,@Param(\"author\") String author);  -->
<select id=\"selectAnimesByConditionUserIf\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
    `cid`,
    `name`,
    `author`,
    `actor`,
    `produce`,
    `create_date`
    from `animes`
    where `create_date` &lt; now()
    <if test=\"cid != null and cid != 0 \">
        cid = #{cid}
    </if>
    <if test=\"author != null\">
        and author like concat(\'%\',#{author},\'%\')
    </if>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` where `create_date` < now() and author like concat(\'%\',?,\'%\')

1.2 测试

@Test
public void testMybatisMapperDynamicSQlUserIf() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    //执行动态SQL，查询动漫列表
    List<Anime> animeList = animeMapper.selectAnimesByConditionUserIf(0, \"土豆\");

    animeList.forEach(System.out::println);
}

2、where + if

• <where><if> 动态标签组合：当where标签中，有if条件成立时，自动增加where关键字，如果所有的if都不成立，也不会多增加where关键字；

• 当where标签中，if成立，增加的SQL语句，前面多出现一个and或者 or关键字，会被自动过滤(剔除),但是末尾出现的，不会被剔除；

• where标签中，也可以增加固定条件，再实际开发过程中，建议where标签中，必须写固定条件，不能全部写if判断；

2.1 SQL

<!--   List<Anime> selectAnimesByConditionUserIfWhere(@Param(\"cid\") Integer cid,@Param(\"author\") String author); -->
<select id=\"selectAnimesByConditionUserIfWhere\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
    `cid`,
    `name`,
    `author`,
    `actor`,
    `produce`,
    `create_date`
    from `animes`
    <where>
        <if test=\"cid != null and cid != 0 \">
            and cid = #{cid}
        </if>
        <if test=\"author != null\">
            and author like concat(\'%\',#{author},\'%\')
        </if>
    </where>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE author like concat(\'%\',?,\'%\')

2.2 测试

@Test
public void testMybatisMapperDynamicSQlUserIfWhere() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    //执行动态SQL，查询动漫列表
    List<Anime> animeList = animeMapper.selectAnimesByConditionUserIfWhere(0, \"土豆\");

    animeList.forEach(System.out::println);
    
}

3、trim + if

• <trim> +<if> :可以实现动态SQL的定制操作，比如：where标签无法屏蔽末尾多出来的and或者or关键字，前缀 和后缀增加的内容，只有标签中的if标签成立，(需要增加条件，才拼接where)；
• prefix:增加前缀固定字符串；
• prefixOverrides：前缀覆盖(自动剔除指定的关键字)；
• suffix：增加后缀固定字符串；
• suffixOverrides：后缀覆盖(自动剔除指定的关键字)；

3.1 SQL

• \"and |or\" 中间一般都会添加一个空格；

<!--  List<Anime> selectAnimesByConditionUserIfTrim(@Param(\"cid\") Integer cid,@Param(\"author\") String author); -->
<select id=\"selectAnimesByConditionUserIfTrim\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
    `cid`,
    `name`,
    `author`,
    `actor`,
    `produce`,
    `create_date`
    from `animes`
    <trim prefix=\" where \"  prefixOverrides=\"and |or\" suffixOverrides=\"and |or\" suffix=\";\">
        <if test=\"cid != null and cid != 0 \">
            cid = #{cid} and
        </if>
        <if test=\"author != null\">
            author like concat(\'%\',#{author},\'%\') and
        </if>
    </trim>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` where author like concat(\'%\',?,\'%\') ;

3.2 测试

@Test
public void testMybatisMapperDynamicSQlUserIfTerm() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    //执行动态SQL，查询动漫列表
    List<Anime> animeList = animeMapper.selectAnimesByConditionUserIfTrim(0, \"土豆\");

    animeList.forEach(System.out::println);

}

4、set + if update

4.1SQL

<!--  int updateAnimeByConditionUserIfSet(Anime animeFOrm); -->
<update id=\"updateAnimeByConditionUserIfSet\">
    update `animes`
    <set>
        <if test=\"cid != null\"> `cid` = #{cid},</if>
        <if test=\"name != null\"> `name` = #{name},</if>
        <if test=\"author != null\"> `author` = #{author},</if>
        <if test=\"actor != null\"> `actor` = #{actor},</if>
        <if test=\"produce != null\"> `produce` = #{produce},</if>
        <if test=\"createDate != null\"> `create_date` = #{createDate},</if>
    </set>
    where `id` = #{id}
</update>

执行SQL:

Preparing: update `animes` SET `name` = ?, `author` = ? where `id` = ?

4.2 测试

@Test
public  void testMybatisMapperDynamicSQlIfSetUpd() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    //模拟前端提供更新参数，实现动态更新，给说明值，就更新什么指端
    Anime animeForm = new Anime();
    animeForm.setId(637);
    animeForm.setName(\"武动乾坤KGC\");
    animeForm.setAuthor(\"土豆KGC\");

    int row = animeMapper.updateAnimeByConditionUserIfSet(animeForm);

    System.out.println(row);

}

5、trim + if update

5.1 SQL

<!--   int updateAnimeByConditionUserIfTrim(Anime animeFOrm); -->
<update id=\"updateAnimeByConditionUserIfTrim\">
    <trim prefix=\"update `animes` set \" prefixOverrides=\",\" suffixOverrides=\",\">
        <if test=\"cid != null\"> `cid` = #{cid},</if>
        <if test=\"name != null\"> `name` = #{name},</if>
        <if test=\"author != null\"> `author` = #{author},</if>
        <if test=\"actor != null\"> `actor` = #{actor},</if>
        <if test=\"produce != null\"> `produce` = #{produce},</if>
        <if test=\"createDate != null\"> `create_date` = #{createDate},</if>
    </trim>
    where `id` = #{id}
</update>

执行SQL:

Preparing: update `animes` set `name` = ?, `author` = ? where `id` = ?

5.2 测试

@Test
public  void testMybatisMapperDynamicSQlIfTrimUpd() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    //模拟前端提供更新参数，实现动态更新，给说明值，就更新什么指端
    Anime animeForm = new Anime();
    animeForm.setId(637);
    animeForm.setName(\"武动乾坤22KGC\");
    animeForm.setAuthor(\"土豆22KGC\");

    int row = animeMapper.updateAnimeByConditionUserIfTrim(animeForm);

    System.out.println(row);

}

6、where + choose + when (判断条件测试)

这个场景主要在传过来的参数，与放进SQL中的参数不一致的时候使用；

比如，前端传过来男/女,但是数据库中查询的时候需要使用1/2;(当然参数也可以在前端或者业务层处理好再放进SQL)

6.1 单引号与双引号的区别

6.1.1 test=\'cid != null and cid == \"1\"\'

test整体用单引号，里面的判断条件双引号；

<!--List<Anime> selectAnimesByConditionUserChooseWhenOtherwise(@Param(\"cid\") String cid); -->
<select id=\"selectAnimesByConditionUserChooseWhenOtherwise\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
    `cid`,
    `name`,
    `author`,
    `actor`,
    `produce`,
    `create_date`
    from `animes`
    <where>
        <choose>
            <!-- test整体使用单引号,判断条件使用双引号  -->
            <when test=\'cid != null  and cid == \"1\"\'>
                and cid = 1
            </when>
            <when test=\'cid != null  and cid == \"2\"\'>
                and cid = 2
            </when>
            <otherwise>
                and cid = 3
            </otherwise>
        </choose>
    </where>
</select>

6.1.1 测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.1.2 test=\"cid != null and cid == \'1\'\"

test整体用双引号，里面的判断条件单引号；

...
<choose>
    <!-- test整体使用双引号,判断条件使用单引号  -->
    <when test=\"cid != null  and cid == \'1\'\">
        and cid = 1
    </when>
    <when test=\"cid != null  and cid == \'2\'\">
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

6.1.2 测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"2\");

执行SQL：

-- SQL没有报错，但是 cid == 2 的条件没有成立，而是走了默认参数 cid = 3
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 3

-- 可以查到数据，但是数据不正确，是cid=3的数据
Anime(id=301, cid=3, name=完美世界, author=辰东, actor=石昊, produce=玄机科技, createDate=Tue Apr 05 00:00:00 CST 2022)

6.1.3 单引号和双引号总结

总结：test整体用单引号，里面的判断条件双引号；

6.2 == 和 eq 的区别

6.2.1 ==

...
<choose>
    <when test=\'cid != null  and cid == \"1\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid == \"2\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

6.2.1 测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.2.2 eq

...
<choose>
    <when test=\'cid != null  and cid eq \"1\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"2\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

6.2.2 测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.3 \"str\" 和 \"str\".toString() 的区别

6.3.1 \"2\" 和 \"2\"toString()

\"2\"

...
<choose>
    <when test=\'cid != null  and cid eq \"1\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"2\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

\"2\".toString()

...
<choose>
     <when test=\'cid != null  and cid eq \"1\".toString()\'>
         and cid = 1
     </when>
     <when test=\'cid != null  and cid eq \"2\".toString()\'>
         and cid = 2
     </when>
     <otherwise>
         and cid = 3
     </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.3.2 \"B\" 和 \"B\".toString() 的区别

\"B\"

...
<choose>
    <when test=\'cid != null  and cid eq \"A\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"B\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"B\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

\"B\".toString()

...
<choose>
    <when test=\'cid != null  and cid eq \"A\".toString()\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"B\".toString()\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"B\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.3.3 \"22\" 和 \"22\".toString()

\"22\"

<choose>
    <when test=\'cid != null  and cid eq \"11\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"22\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"22\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

\"22\".toString()

...
<choose>
    <when test=\'cid != null  and cid eq \"11\"toString()\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"22\"toString()\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"22\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.3.4 \"BB\" 和 \"BB\".toString()

\"BB\"

...
<choose>
    <when test=\'cid != null  and cid eq \"AA\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"BB\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"BB\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

\"BB\".toString()

...
<choose>
    <when test=\'cid != null  and cid eq \"AA\".toString()\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"BB\".toString()\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"BB\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.3.5 \"任意字符2\" 和 \"任意字符2\".toString()

\"任意字符2\"

...
<choose>
    <when test=\'cid != null  and cid eq \"任意字符1\"\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"任意字符2\"\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"任意字符2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

\"任意字符2\".toString()

...
<choose>
    <when test=\'cid != null  and cid eq \"任意字符1\".toString()\'>
        and cid = 1
    </when>
    <when test=\'cid != null  and cid eq \"任意字符2\".toString()\'>
        and cid = 2
    </when>
    <otherwise>
        and cid = 3
    </otherwise>
</choose>
...

测试

List<Anime> animeList = animeMapper.selectAnimesByConditionUserChooseWhenOtherwise(\"任意字符2\");

执行SQL:

-- SQL正常
Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE cid = 2

-- 可以查到正确数据
Anime(id=201, cid=2, name=海贼王, author=尾田, actor=路飞, produce=腾讯动漫, createDate=Tue Apr 05 00:00:00 CST 2022)
Anime(id=627, cid=2, name=魁拔3, author=青春树, actor=蛮吉, produce=青春树, createDate=Tue Jan 07 00:00:00 CST 2003)

6.4 总结

只需要将test整体用单引号，里面的判断条件双引号，就可以，加不加.toString(),并不影响；

7、foreach

根据id集合查询动漫集合；

7.1 SQL

7.1.1 起别名 where + foreach (in)

使用 in;

<!--List<Anime> selectAnimesByConditionUserForeach(@Param(\"ids\") List<Integer> ids);-->
<select id=\"selectAnimesByConditionUserForeach\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
            `cid`,
            `name`,
            `author`,
            `actor`,
            `produce`,
            `create_date`
    from `animes`
	<where>
        <foreach collection=\"ids\" item=\"id\" open=\"id in(\" close=\" )\" separator=\", \">
            #{id}
        </foreach>
	</where>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE id in( ? , ? , ? )

7.1.2 不起别名 where + foreach (in)

使用 in;

<!--   List<Anime> selectAnimesByConditionUserForeach( List<Integer> ids);  -->
<select id=\"selectAnimesByConditionUserForeach\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
            `cid`,
            `name`,
            `author`,
            `actor`,
            `produce`,
            `create_date`
    from `animes`
    <where>
        <foreach collection=\"list\" item=\"id\" open=\"id in(\" close=\" )\" separator=\", \">
            #{id}
        </foreach>
    </where>   
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` WHERE id in( ? , ? , ? )

7.1.3 起别名 foreach (in)

不用where标签;

使用 in;

<!--List<Anime> selectAnimesByConditionUserForeach(@Param(\"ids\") List<Integer> ids);-->
<select id=\"selectAnimesByConditionUserForeach\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
            `cid`,
            `name`,
            `author`,
            `actor`,
            `produce`,
            `create_date`
    from `animes`
    <foreach collection=\"ids\" item=\"id\" open=\" where id in(\" close=\" )\" separator=\", \">
        #{id}
    </foreach>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` where id in( ? , ? , ? )

7.1.4 起别名 trim + foreach （in）

不用where标签;

使用 in;

通过7.1.3和7.1.4 可以总结，trim 和 foreach 都有前缀，后缀和分隔符，可以根据情况进项选择使用；

<!--List<Anime> selectAnimesByConditionUserForeach(@Param(\"ids\") List<Integer> ids);-->
<select id=\"selectAnimesByConditionUserForeach\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
            `cid`,
            `name`,
            `author`,
            `actor`,
            `produce`,
            `create_date`
    from `animes`
	<trim prefix=\" where id in \">
        <foreach collection=\"ids\" item=\"id\" open=\" (\" close=\" )\" separator=\", \">
            #{id}
        </foreach>
     </trim>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` where id in ( ? , ? , ? )

7.1.5 起别名 foreach （or）

不用where标签;

使用 or;

<!--List<Anime> selectAnimesByConditionUserForeach(@Param(\"ids\") List<Integer> ids);-->
<select id=\"selectAnimesByConditionUserForeach\" resultType=\"com.kgc.mybatis.bean.Anime\">
    select  `id`,
            `cid`,
            `name`,
            `author`,
            `actor`,
            `produce`,
            `create_date`
    from `animes`
    <foreach collection=\"ids\" item=\"id\" open=\" where \" close=\" \" separator=\" or \">
        id = #{id}
    </foreach>
</select>

执行SQL:

Preparing: select `id`, `cid`, `name`, `author`, `actor`, `produce`, `create_date` from `animes` where id = ? or id = ? or id = ?

7.2 测试

@Test
public void testMybatisMapperDynamicSQlUserForeach() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    //执行动态SQL，查询动漫列表
    List<Anime> animeList = animeMapper.selectAnimesByConditionUserForeach(Arrays.asList(101,102,103));

    animeList.forEach(System.out::println);

}

8、trim + if insert

8.1 SQL

<!-- int insertAnimeByConditionIfTrim(Anime animeForm); -->
<insert id=\"insertAnimeByConditionIfTrim\">
    <trim prefix=\"insert into `animes` ( \" suffix=\")\" suffixOverrides=\",\">
        <if test=\"cid != null\"> `cid`,</if>
        <if test=\"name != null\"> `name`,</if>
        <if test=\"author != null\"> `author`,</if>
        <if test=\"actor != null\"> `actor`,</if>
        <if test=\"produce != null\"> `produce`,</if>
        <if test=\"createDate != null\"> `create_date`,</if>
    </trim>
    <trim prefix=\"values ( \" suffix=\")\" suffixOverrides=\",\">
        <if test=\"cid != null\"> #{cid},</if>
        <if test=\"name != null\"> #{name},</if>
        <if test=\"author != null\"> #{author},</if>
        <if test=\"actor != null\"> #{actor},</if>
        <if test=\"produce != null\"> #{produce},</if>
        <if test=\"createDate != null\"> #{createDate},</if>
    </trim>
</insert>

执行SQL:

insert into `animes` ( `cid`, `name`, `author`, `actor`, `produce` ) values ( ?, ?, ?, ?, ? )

8.2 测试

@Test
public  void testMybatisMapperDynamicSQlIfTrimInsert() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    Anime animeForm = new Anime();
    animeForm.setCid(1);
    animeForm.setName(\"知否知否\");
    animeForm.setAuthor(\"关心则乱\");
    animeForm.setActor(\"明兰\");
    animeForm.setProduce(\"优酷\");

    //指定if+ trim 冬天SQL,新增动漫
    int row = animeMapper.insertAnimeByConditionIfTrim(animeForm);

    System.out.println(row);
}

9、@ Select

使用注释添加动漫；

9.1 SQL

@Select(\"select `id`,`cid`,`name`,`author`,`actor`,`produce`,`create_date` from `animes` where id = #{id} \")
Anime selectAnimesByConditionUserAnnotationSelect(Integer id);

执行SQL:

Preparing: select `id`,`cid`,`name`,`author`,`actor`,`produce`,`create_date` from `animes` where id = ?

9.2 测试

@Test
public  void  testAnimesByConditionUserAnnotationSelect() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    Anime anime = animeMapper.selectAnimesByConditionUserAnnotationSelect(653);

    System.out.println(anime);

}

10、@Delete 批量删除

10.1 SQL

@Delete({\"<script>\",
            \"delete from `animes`\",
            \"<foreach collection=\'ids\' item=\'id\' open=\' where id in ( \' close= \' ) \' separator= \' , \'> \" ,
            \"      #{id} \",
            \"</foreach>\" ,
            \"</script>\"})
int deleteAnimesByConditionUserAnnotationDelete(@Param(\"ids\") List<Integer> ids);

执行SQL:

Preparing: delete from `animes` where id in ( ? , ? , ? )

10.2 测试

@Test
public void testDeleteAnimesByConditionUserAnnotationDelete() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    int row = animeMapper.deleteAnimesByConditionUserAnnotationDelete(Arrays.asList(649, 651, 652));

    System.out.println(row);

}

11、批量加入动漫分类

11.1 SQL

<!-- int insertCategoryBatchUserFoeEach(List<Category> categoryList) -->
<!-- int insertCategoryBatchUserFoeEach(@Param(\"categoryList\") List<Category> categoryList); -->
<insert id=\"insertCategoryBatchUserFoeEach\" >
    insert into `category` (`name`) values
    <!-- 
    默认参数：collection(不自定义参数名的时候可以使用Available parameters are [collection, list])
    自定义参数：categoryList 
    -->
    <foreach collection=\"collection\" item=\"category\" separator=\", \">
        (#{category.name})
    </foreach>
</insert>

执行SQL:

Preparing: insert into `category` (`name`) values (?) , (?) , (?)

11.2 测试

@Test
public void testInsertCategoryBatchUserFoeEach() throws IOException {
    SqlSession defaultSqlSession = getSqlSessionFactory().openSession(true);

    //获取mapper接口的代理实现类对象
    AnimeMapper animeMapper = defaultSqlSession.getMapper(AnimeMapper.class);

    Category category1 = new Category();
    Category category2 = new Category();
    Category category3 = new Category();
    category1.setName(\"aaa\");
    category2.setName(\"bbb\");
    category3.setName(\"ccc\");

    List<Category> categoryList = new ArrayList<>();
    categoryList.add(category1);
    categoryList.add(category2);
    categoryList.add(category3);

    int row = animeMapper.insertCategoryBatchUserFoeEach(categoryList);

    System.out.println(row);

}

来源：https://www.cnblogs.com/xiaoqigui/p/16619854.html
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