在mybatis中動態使用HashMap進行參數映射

Question

好的，所以這是使用 ibatis 將 HashMap 值插入表這個問題的重新發布（但我正在尋找不同的方式 - 答案對我不起作用）。

DB1GetStudentDataMapper.xml （查詢一個數據庫）

<?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="com.testing.db1.DB1GetStudentDataMapper">

<select id="selectAllStudents" resultType="java.util.Map">
        SELECT STUDENT_CD, STUDENT_NM, PARENT_CD, CREATED_DATE
        FROM STUDENT
        WHERE STD_STATUS='ACT'
</select>

</mapper>

DB2InsertStudentMapper.xml （這個查詢到不同的數據庫）

<?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="com.testing.db2.DB2InsertStudentMapper">
                
<insert id="insertStudent" parameterType="java.util.HashMap">
  INSERT INTO STUDENT
  <!-- dynamically select column names from hashmap -->
  (#{stdMap.keySet}) // this is not working - its coming as null
   <!-- dynamically select values for the above columns from hashmap -->
   VALUES (#{stdMap.values}) // this is not working - its coming as null
</insert>
           
</mapper>

DB2InsertStudentMapper.java

public interface TMODSBDataRefreshMapper {
    
    void insertStudent(@Param("stdMap") HashMap stdMap);
}

學生數據處理程序

public class Student {
    
    // I have defaultExecutorType as BATCH in my mapper config file
    
        private DB1GetStudentDataMapper db1Mapper; // Interface Mapper for first data source
        private DB2InsertStudentMapper db2Mapper; // Interface Mapper for second data source
        
        public processStudent() throws Exception {
            
            List<HashMap> rs = db1Mapper.selectAllStudents(); // Gets some 15k+ records
            for(int i =0; i < rs.size(); i++) { // so this will loop through 15k+ records
                HashMap result = rs.get(i);
                System.out.println(result.keySet()); // prints column names from select query [STUDENT_CD, STUDENT_NM, PARENT_CD, CREATED_DATE]
                System.out.println(result.values()); // prints above column values of first data set [1001, Mike, 5001, 2021-07-01]
                
                // All I am trying is to insert above 15k records into different database dynamically rather than creating POJO
                db2Mapper.insertStudent(result);
            }
            
        }
            
}

注意：例如，我使用了 4 列 - 我有大約 150 多列可以使用..

PS：請記住，當您使用較少的列時，此解決方案效果更好 - 但如果您有批量插入，則效果不佳 - 它會影響性能。

Answer 1

使用<foreach />迭代映射時，鍵和值分別分配給index和item指定的變量。
所以，你的插入語句應該是這樣的。

<insert id="insertStudent">
  INSERT INTO STUDENT (
    <foreach collection="stdMap" index="col" separator=",">
      ${col}
    </foreach>
  ) VALUES (
    <foreach collection="stdMap" item="val" separator=",">
      #{val}
    </foreach>
  )
</insert>

• 您必須使用${}作為列名，並使用#{}作為值。 有關詳細信息，請參閱常見問題解答。
• 要以相同的順序迭代地圖，您應該使用java.util.LinkedHashMap作為<select />的結果類型。