MyBatis | Mapping Query Results to Arbitrary Java Objects | Defining Mappings with a Class

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Code

sample_mapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="sample.mybatis">
  <resultMap id="testTableResultMap" type="sample.mybatis.TestTable">
    <id property="id" column="id" />
    <result property="value" column="value" />
  </resultMap>

  <select id="selectTest" resultMap="testTableResultMap">
    select * from test_table
  </select>
</mapper>

Explanation

  • Use the <resultMap> tag to define the mapping between query results and a Java class.
  • Define identifier properties with the <id> tag.
    • An identifier property is a property used to identify an instance.
    • Specifying identifier properties appears to improve performance for caching and JOIN mappings.
    • Specify the Java-side property or field name in the property attribute.
    • Specify the database-side column name in the column attribute.
  • Define each column mapping with the <result> tag.
    • Here as well, map the property name and column name.
  • Define a name that uniquely identifies the mapping with the id attribute of <resultMap> (testTableResultMap).
    • Specify this name in the resultMap attribute of the <select> tag.