mybatis中动态使用HashMap进行参数映射

Question

好吧，这是对这个问题的重新发布 Inserting HashMap Values to a table using ibatis（但我正在寻找一种不同的方式 - 答案对我不起作用）..

DB1GetStudentDataMapper.xml（查询到一个数据库）

<?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（这个查询到不同的数据库）

<?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);
}

StudentDataProcess.java

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);
            }
            
        }
            
}

Note: Just for example I used 4 columns - I have some 150+ columns to work with..

PS：请记住，当您使用较少的列时，此解决方案效果更好 - 但如果您有批量插入则效果不佳 - 它会影响性能。

Answer 1

当使用 <foreach /> 迭代映射时，键和值分别分配给 index 和 item 中指定的变量。
因此，您的插入语句应如下所示。

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

列名必须使用 ${}，值必须使用 #{}。详情见FAQ。
要以相同的顺序迭代地图，您应该使用 java.util.LinkedHashMap 作为 <select /> 的结果类型。

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