标签：from jdb nbsp rri app 表示 包含 详解 复制
MyBatis的动态SQL是基于OGNL表达式的，它可以帮助我们方便的在SQL语句中实现某些逻辑。
MyBatis中用于实现动态SQL的元素主要有：
1 <select id="dynamicIfTest" parameterType="Blog" resultType="Blog">
2 select * from t_blog where 11 = 1
3 <if test="title != null">
4 and title = #{title}
5 </if>
6 <if test="content != null">
7 and content = #{content}
8 </if>
9 <if test="owner != null">
10 and owner = #{owner}
11 </if>
12 </select>
1 <select id="dynamicChooseTest" parameterType="Blog" resultType="Blog">
2 select * from t_blog where 11 = 1
3 <choose>
4 <when test="title != null">
5 and title = #{title}
6 </when>
7 <when test="content != null">
8 and content = #{content}
9 </when>
10 <otherwise>
11 and owner = "owner1"
12 </otherwise>
13 </choose>
14 </select>
1 <select id="dynamicWhereTest" parameterType="Blog" resultType="Blog">
2 select * from t_blog
3 <where>
4 <if test="title != null">
5 title = #{title}
6 </if>
7 <if test="content != null">
8 and content = #{content}
9 </if>
10 <if test="owner != null">
11 and owner = #{owner}
12 </if>
13 </where>
14 </select>
1 <select id="dynamicTrimTest" parameterType="Blog" resultType="Blog">
2 select * from t_blog
3 <trim prefix="where" prefixOverrides="and |or">
4 <if test="title != null">
5 title = #{title}
6 </if>
7 <if test="content != null">
8 and content = #{content}
9 </if>
10 <if test="owner != null">
11 or owner = #{owner}
12 </if>
13 </trim>
14 </select>
set元素主要是用在更新操作的时候，它的主要功能和where元素其实是差不多的，主要是在包含的语句前输出一个set，然后如果包含的语句是以逗号结束的话将会把该逗号忽略，如果set包含的内容为空的话则会出错。有了set元素我们就可以动态的更新那些修改了的字段。下面是一段示例代码：
1 <update id="dynamicSetTest" parameterType="Blog">
2 update t_blog
3 <set>
4 <if test="title != null">
5 title = #{title},
6 </if>
7 <if test="content != null">
8 content = #{content},
9 </if>
10 <if test="owner != null">
11 owner = #{owner}
12 </if>
13 </set>
14 where id = #{id}
15 </update>
1 <select id="dynamicForeachTest" resultType="Blog">
2 select * from t_blog where id in
3 <foreach collection="list" index="index" item="item" open="(" separator="," close=")">
4 #{item}
5 </foreach>
6 </select>
上述collection的值为list，对应的Mapper是这样的
public List<Blog> dynamicForeachTest(List<Integer> ids);
测试代码：
1 @Test
2 public void dynamicForeachTest() {
3 SqlSession session = Util.getSqlSessionFactory().openSession();
4 BlogMapper blogMapper = session.getMapper(BlogMapper.class);
5 List<Integer> ids = new ArrayList<Integer>();
6 ids.add(1);
7 ids.add(3);
8 ids.add(6);
9 List<Blog> blogs = blogMapper.dynamicForeachTest(ids);
10 for (Blog blog : blogs)
11 System.out.println(blog);
12 session.close();
13 }
2.单参数array数组的类型：
1 <select id="dynamicForeach2Test" resultType="Blog">
2 select * from t_blog where id in
3 <foreach collection="array" index="index" item="item" open="(" separator="," close=")">
4 #{item}
5 </foreach>
6 </select>
上述collection为array，对应的Mapper代码：
public List<Blog> dynamicForeach2Test(int[] ids);
对应的测试代码：
1 @Test
2 public void dynamicForeach2Test() {
3 SqlSession session = Util.getSqlSessionFactory().openSession();
4 BlogMapper blogMapper = session.getMapper(BlogMapper.class);
5 int[] ids = new int[] {1,3,6,9};
6 List<Blog> blogs = blogMapper.dynamicForeach2Test(ids);
7 for (Blog blog : blogs)
8 System.out.println(blog);
9 session.close();
10 }
3.自己把参数封装成Map的类型
1 <select id="dynamicForeach3Test" resultType="Blog">
2 select * from t_blog where title like "%"#{title}"%" and id in
3 <foreach collection="ids" index="index" item="item" open="(" separator="," close=")">
4 #{item}
5 </foreach>
6 </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<Blog> dynamicForeach3Test(Map<String, Object> params);
对应测试代码：
1 @Test
2 public void dynamicForeach3Test() {
3 SqlSession session = Util.getSqlSessionFactory().openSession();
4 BlogMapper blogMapper = session.getMapper(BlogMapper.class);
5 final List<Integer> ids = new ArrayList<Integer>();
6 ids.add(1);
7 ids.add(2);
8 ids.add(3);
9 ids.add(6);
10 ids.add(7);
11 ids.add(9);
12 Map<String, Object> params = new HashMap<String, Object>();
13 params.put("ids", ids);
14 params.put("title", "中国");
15 List<Blog> blogs = blogMapper.dynamicForeach3Test(params);
16 for (Blog blog : blogs)
17 System.out.println(blog);
18 session.close();
19 }
标签：from jdb nbsp rri app 表示 包含 详解 复制
原文地址：http://www.cnblogs.com/efforts-will-be-lucky/p/7388806.html
