MyBatis动态标签

常见的动态标签

1. if

2. choose, when, otherwise

3. trim,where,set

4. foreach

5. bind

6. sql

   mybatis通过OGNL表达式来进行取值操作;比如:#{username}

Mybatis两个内置参数

1. _parameter: 如果接口传入多个参数,这些参数都包含在这一个参数中,如果传入一个,那该参数就代表传来的参数

2. _databaseId: 如果在mybatis核心配置文件中配置了databaseIdProvider(数据库厂商)标签,则该参数代表当前数据库厂商别名
   这两个参数可以搭配if标签来使用,

   <if text="_databaseId == 'mysql'">
       SELECT * FROM user
   	<if text="_parameter != null">
       	WHERE username = #{_parameter.属性名}
       if>
   if>
   

1. if使用

<if test="title != null">
    AND title like #{title}
if>

2. choose使用

<choose>
    
    <when test="title != null">
        AND title like #{title}
    when>
    <when test="author != null and author.name != null">
        AND author_name like #{author.name}
    when>
    <otherwise>
        AND featured = 1
    otherwise>
choose>

3. trim使用

<trim prefix="WHERE" prefixOverrides="AND | OR" suffix="" suffixOverrides="">
  ...
trim>

4. set使用

<update id="updateAuthorIfNecessary">
  update Author
    <set>
      <if test="username != null">username=#{username},if>
      <if test="password != null">password=#{password},if>
      <if test="email != null">email=#{email},if>
      <if test="bio != null">bio=#{bio}if>
    set>
  where id=#{id}
update>

5. foreach使用

<select id="selectPostIn" resultType="domain.blog.Post">
  SELECT *
  FROM POST P
  WHERE ID in
  <foreach item="item" index="index" collection="list" open="(" separator="," close=")">
        #{item}
  foreach>
select>

<insert id="insertTest">
	INSERT INTO user_tbl(id,name)
    VALUES
    <foreach collection="userList" item="user" separator=",">
    	(#{user.id}, #{user.name})
    foreach>
insert>

6. bind使用

<select id="selectBlogsLike" resultType="Blog">
  <bind name="likename" value="'%' + #{username} + '%'" />
  SELECT * FROM BLOG
  WHERE title LIKE #{likename}
select>

7. sql使用

<sql id="userColumns"> ${alias}.id,${alias}.username,${alias}.password sql>
<select id="selectUsers" resultType="map">
  select
    <include refid="userColumns"><property name="alias" value="t1"/>include>,
    <include refid="userColumns"><property name="alias" value="t2"/>include>
  from some_table t1
    cross join some_table t2
select>