Sample code to query user by id using mybatis

mapper xml

<select id="queryUserById" parameterType="long" resultType="User">
    SELECT
        *
    FROM
        user
    WHERE
        user_id = #{userId}
</select>

Java mapper interface

User queryUserById(@Param(value="userId")long id);

| Name | Description | | ------- |:-----------:| | id | unique id to reference method in mapper interface | | parameterType | optional attribute(MyBatis can calculate the TypeHandler to use out of the actual parameter passed to the statement) |

Single Parameter Type Usage

parameterType="long" -> types of all parameters should all be long

Multiple Parameter Type Using Map

<select id="queryUser" parameterType="Map" resultType="User">
    SELECT
        *
    FROM
        user
    WHERE
        user_id = #{userId} and username = #{username}
</select>

Map<String,String> map=new HasMap<String,String>();
map.put("userId","2");
map.put("username", "name");

User queryUser(map);

Multiple Parameter Type Using Annotation

(note: if you only have one parameter and it's Javabean, you can skip the annotation)

<select id="queryUser" resultType="User">
    SELECT
        *
    FROM
        user
    WHERE
        user_id = #{userId} and username = #{username}
</select>

User queryUser(@Param(value="userId") long id, @Param(value="username") long username);

difference between #{} and ${}

you can pass parameter using #{} and ${} in mapper xml

| Name | Description | | ------- |:-----------:| | #{...} | a parameter marker in a JDBC prepared statement | | ${...} | string substitution |

Note:

use of ${...} (string substitution) presents a risk for SQL injection attacks. Also, string substitution can be problematical for complex types like dates. For these reasons, mybatis recommends using the #{...} form whenever possible. link

ResultType and ResultMap Usage

resultType="User" -> return User object or list of User objects if you only want some of the data in user pojo, you can use resultMap to get subset data in User data

<resultMap id="userResultMap" type="User">
  <id property="userId" column="user_id" />
  <result property="username" column="username"/>
  <result property="password" column="password"/>
</resultMap>

<select id="selectUsers" resultMap="userResultMap">
  select user_id, username, password
  from user
  where id = #{userId}
</select>