本文介紹了在Mybatis中動態使用HashMap進行參數映射的處理方法，對大家解決問題具有一定的參考價值，需要的朋友們下面隨著小編來一起學習吧！
問題描述
好的，這是對這個問題的重新發布Inserting HashMap Values to a table using ibatis(但我正在尋找不同的方法-答案對我不起作用)。
DB1GetStudentDataMapper.xml(這查詢一個數據庫)
<?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);
}
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);
}
}
}
注意：僅舉個例子，我使用了4列-我有大約150多列要處理..
PS：請記住，此解決方案在使用較少列時效果較好，但如果使用大容量插入則效果不佳，它會影響性能。
推薦答案
使用<foreach />迭代映射時，鍵和值會分別賦給index和item中指定的變量。
因此，您的INSERT語句應該如下所示。
<insert id="insertStudent">
INSERT INTO STUDENT (
<foreach collection="stdMap" index="col" separator=",">
${col}
</foreach>
) VALUES (
<foreach collection="stdMap" item="val" separator=",">
#{val}
</foreach>
)
</insert>
必須使用${}表示列名，使用#{}表示值。有關詳細信息，請參閱FAQ。
若要以相同的順序迭代映射，應使用java.util.LinkedHashMap作為<select />的結果類型。
這篇關于在Mybatis中動態使用HashMap進行參數映射的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，
