mybatis 中 foreach collection的三种用法

如果传入的是单参数且参数类型是一个List的时候，collection属性值为list
如果传入的是单参数且参数类型是一个array数组的时候，collection的属性值为array
如果传入的参数是多个的时候，我们就需要把它们封装成一个Map了，当然单参数也可以
代码：
1.单参数List的类型：

 <select id="dynamicForeachTest" parameterType="java.util.List" resultType="Blog">
           select * from t_blog where id in
       <foreach collection="list" index="index" item="item" open="(" separator="," close=")">
                #{item}       
       </foreach>    
    </select>

上述collection的值为list，对应的Mapper是这样的
public List dynamicForeachTest(List ids);
测试代码：

 @Test
     public void dynamicForeachTest() {
         SqlSession session = Util.getSqlSessionFactory().openSession();      
          BlogMapper blogMapper = session.getMapper(BlogMapper.class);
          List ids = new ArrayList();
          ids.add(1);
          ids.add(3);
          ids.add(6);
       List blogs = blogMapper.dynamicForeachTest(ids);
        for (Blog blog : blogs)
              System.out.println(blog);
         session.close();
     }

2.单参数array数组的类型：

 <select id="dynamicForeach2Test" parameterType="java.util.ArrayList" resultType="Blog">
     select * from t_blog where id in
     <foreach collection="array" index="index" item="item" open="(" separator="," close=")">
          #{item}
     </foreach>
 </select>

上述collection为array，对应的Mapper代码：
public List dynamicForeach2Test(int[] ids);
对应的测试代码：

  @Test
public void dynamicForeach2Test() {
         SqlSession session = Util.getSqlSessionFactory().openSession();
        BlogMapper blogMapper = session.getMapper(BlogMapper.class);
         int[] ids = new int[] {1,3,6,9};
        List blogs = blogMapper.dynamicForeach2Test(ids);
         for (Blog blog : blogs)
       System.out.println(blog);    
         session.close();
 }

3.自己把参数封装成Map的类型

 <select id="dynamicForeach3Test" parameterType="java.util.HashMap" resultType="Blog">
        select * from t_blog where title like "%"#{title}"%" and id in
          <foreach collection="ids" index="index" item="item" open="(" separator="," close=")">
               #{item}
          </foreach>
 </select>

上述collection的值为ids，是传入的参数Map的key，对应的Mapper代码：
public List dynamicForeach3Test(Map params);
对应测试代码：

@Test
    public void dynamicForeach3Test() {
        SqlSession session = Util.getSqlSessionFactory().openSession();
         BlogMapper blogMapper = session.getMapper(BlogMapper.class);
          final List ids = new ArrayList();
          ids.add(1);
          ids.add(2);
          ids.add(3);
          ids.add(6);
         ids.add(7);
         ids.add(9);
        Map params = new HashMap();
         params.put("ids", ids);
         params.put("title", "中国");
        List blogs = blogMapper.dynamicForeach3Test(params);
         for (Blog blog : blogs)
             System.out.println(blog);
         session.close();
     }
     ```

来源：https://blog.csdn.net/qq_28643817/article/details/100896739

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