mapper. Comments in XML files

Annotation mode

stay mapper.xml In file , The annotation method is <!--existence of query content-->, Direct adoption Java Comments of code way /*existence of query content*/ Will report a mistake , Especially in SQL sentence When this annotation method appears in .

‘ Invalid column index ’bug And solve

You need to verify the data when importing data yesterday , stay mapper Query the data in the table in the file , Will be voided sql Select Java The way , Error will be reported at this time .

<select id="getSeqNameCount" parameterClass="java.util.HashMap" resultClass="java.lang.Integer">
	SELECT COUNT(*) COUN FROM tablename A
		WHERE  A.id=#id#  and  A.name=#name#
	/*SELECT * FROM tablename A WHERE A.id=#id# and A.name=#name#*/
	</select>

    
     

During parsing, the parameter position will be parsed as a placeholder ‘？’, So now the following sql It will be parsed in the background as follows , But there are only two parameters passed in , So I will report at this time “Caused by: java.sql.SQLException: Invalid column index ”, Because the number of parameters and placeholders passed in varies .

SELECT COUNT(*) COUN FROM tablename A WHERE A.id=? and A.name=?
	/*SELECT * FROM tablename A WHERE A.id=? and A.name=?/ 
    
     

summary

1、mapper.xml The annotation method in the document is <!--existence of query content-->;
2、 “Caused by: java.sql.SQLException: Invalid column index ” Errors are generally caused by sql Placeholders in statements cause ：
1 The number of incoming parameters is different from the number of placeholders ;
2SQL Placeholders in statements ？ It's the Chinese version ;
3SQL Placeholders in statements ？ Put in a string ;