How to dynamically change the column name acquired by MyBatis

How to dynamically change the column name acquired by MyBatis

In order to dynamically pass the condition value of where clause in MyBatis, I think that it is common to treat it as a prepared statement using "#" as shown below.

SQL definition file.xml


<select id="getHogeValue" resultType="java.util.Map">
select * 
form hoge_table
where foo_1 = #{foovalue}
</select>

This section describes how to dynamically change the column to be acquired. In other words, it is useful when the column specified in the select clause is indefinite.

environment

Java:JDK1.7 MyBatis:mybatis-3.2.5.jar

Implementation method

Instead of passing it as a prepared statement value Use "$" to pass as a string.

Below is an example.

Data access class.java


    //Define the dynamic part of the column name in List
    List<Integer> columnIdList = Arrays.asList(1,2,3,4);
    
    //Set List of column name dynamic part as Map
    Map params = new HashMap();
    params.put("column_id_list", columnIdList);
    
    //FOO from Hoge table_1, FOO_2, FOO_3, FOO_4, BAR_1, BAR_2, BAR_3, BAR_Get 4
    List<Map> hogeValueLsit = hogeTableMapper.getHogeValue(params);
    
    //Check the acquired contents
    for (Map elm : hogeValueLsit) {
      int idx = 0;
      for (Integer columnId : columnIdList) {
        
        String foo = (String)elm.get("FOO_"+columnId);
        System.out.println("FOO_" + idx + "The second is" + foo + "is.");
        
        String bar = (String)elm.get("BAR_"+columnId);
        System.out.println("BAR_" + idx + "The second is" + bar + "is.");
        
      }
    }

SQL definition file.xml


    <select id="getHogeValue" resultType="java.util.Map">
    select 
      <foreach item="column_id" collection="column_id_list">
         foo_${column_id}
        ,bar_${column_id}
      </foreach>
    from hoge_table 
    </select>

important point

Note that the column name is "uppercase" when retrieving on the Java side Even if the SQL definition file side uses lowercase "foo_" The Map key on the Java side can only be obtained with "FOO_" in uppercase.

that's all.

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