[MySQL project practical optimization] complex trigger case sharing

Last one  mysql  The review article of  

trigger

  Basic operation , This article , Share a case I encountered in the project

Original requirements

The person in charge wants the data in the BOM , After being changed by others , You need to leave traces in the system , such as , Record 1, At a certain time , By someone , What data has been updated , Old values of these data , And new values , Why do we separate

Besides , The person in charge also needs to know  

The data has been updated

  This action , Facilitate some work adjustment （ Cross department の pain ）

Demand analysis

Intuitive feeling , When the table is updating , Relevant data need to be recorded , It is better to store these data in a new , In a table similar to a log

Consider two options ：

One 、 Use  aop

adopt  aop , Locate the section to the corresponding  

xxMapper.update

  On the way , When  java  Before performing the update operation ,aop  Also began to work , The working logic at this time is as follows ：

• Method call in  update, Trigger  aop  section

• stay  aop  in , Go first  DB  The existing data of the corresponding record is obtained from the corresponding table

• Compare new 、 The value of each attribute in the old two copies of data , Record the changed data

• Data that will change , Record to the library

• Beautify the data display format , Send this data to the person in charge

This plan , Basically in  java  To realize this function , Not good or bad , The compasses

Two 、 Use triggers

The whole logic is similar to the previous scheme , Similarly, we need to compare the old and new values + Record , And notify the addressee

however , This is at the database level , And when the trigger is triggered , You can get two versions of data directly , also , stay  mysql  Some logical operations are also supported in

Final , Consider adopting the scheme 2, dedicated , The coupling of source code is low , Can't use it  java  Add  aop  Code and processing logic

Design log table

The core elements of the log table ：

• Who did it

• Which record was moved

• Time of operation

• Changing data

• Whether this log record has been processed （ If a notice has been sent ）

Final table building  sql  See below ：

drop table if EXISTS mdm_basics_change_log;
create table mdm_basics_change_log(
 id BIGINT PRIMARY key auto_increment COMMENT 'id',
 mdm_code varchar(50) COMMENT ' Material code ',
 update_by varchar(20) COMMENT ' Update person's account ',
 update_name varchar(20) COMMENT ' Update the name of the person ',
 update_date TIMESTAMP DEFAULT now() COMMENT ' Date of update ',
 change_data LONGTEXT COMMENT ' Changed data ',
 notified int default 0 COMMENT ' Has the person in charge been notified '
);


Trigger function analysis

There are  

val1 -> val2

  This state , That can only be

Trigger before update

Because there are too many fields in the material table （70+ Column ）, And it may not be all used , It is not convenient to map and store one by one in the log table , Like records 1  It was used  

col1, col2

 , Record 2  It was used  

col1, col3

, Then a suitable solution is , In the form of strings , Store changing data , Then the storage format is defined as follows ：

Field 1_ The old value _ The new value
Field 3_ The old value _ The new value


When the trigger is executed , We need to check the old and new values of the fields we focus on one by one , Is it consistent , In case of inconsistency , It needs to be recorded , Append to temporary string variables  str  On

When all the inspections are completed , We judge  str  Is the value of  

''

, If yes, there is no need to record it in the log table

At the notification stage , Directly intercept this string + After formatting the display , Then send it to the person in charge by email  

This article will not focus on this detail

Trigger writing

From the above analysis , You can specify that the body of the trigger will have many  sql  operation , So we need to use  

begin end

  Code block

You need to use a string type  

str

  Variable receives the result of splicing

Need to use  

IF

  Judge whether the old and new values of key fields have changed , Only in changing circumstances , It needs to be spliced to  

str

  variable

Handle the splicing in  

str

  After the data of , Then judge by conditions , Whether the record needs to be inserted into the log table

The final effect of the trigger is as follows （ A lot of space is omitted  

if

  Old and new value judgment ）：

DELIMITER //
drop TRIGGER if EXISTS trigger_recordMdmBasicsUpdate ;
CREATE TRIGGER trigger_recordMdmBasicsUpdate BEFORE UPDATE ON mdm_basics FOR EACH ROW
BEGIN
 DECLARE str LONGTEXT DEFAULT '';
 DECLARE split_op LONGTEXT DEFAULT ',,.';
 IF old.mdm_name!=new.mdm_name THEN
 set str = CONCAT_WS(split_op,' Material name ',old.mdm_name,new.mdm_name,'\n');
 END IF;
 IF old.mdm_note!=new.mdm_note THEN
 set str = CONCAT_WS(split_op,' Material description ( chinese )',old.mdm_note,new.mdm_note,'\n');
 END IF;
 if str != '' and old.mdm_code != '' then 
 insert into mdm_basics_change_log(mdm_code,update_by,update_name,change_data) VALUES (new.mdm_code,new.update_by,new.update_name,str);
 end if;
END
//
DELIMITER ;