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mysqlmysql-cluster

MySQL NDB Events - listening for changes to specific row

I'm using Events in the NDB API. I'm wondering if it is possible to listen for events based upon a particular row...

For example: 

CREATE TABLE mytable( id int(11) NOT NULL AUTO_INCREMENT, 
                      name  varchar(40), 
                      PRIMARY KEY(id) );

INSERT INTO mytable values(NULL,'john');
INSERT INTO mytable values(NULL,'sallie');
INSERT INTO mytable values(NULL,'martin');
INSERT INTO mytable values(NULL,'alex');

So, now we have a table(mytable) with two columns. And we have added 4 rows.

In my examples testing the NDB API, I am able to tell when one of these names has been changed. So, say we change 'john' to 'jim'. In my code, after pollEvents() and getValue(), I am able to see that 'john' has changed to 'jim' by looking the contents of NdbRecAttr.

But, is there a way to only listen for changes to a specific id(row)?

For example, say I wanted to know when the name 'alex'(PK id = 4) has been changed.

Is this possible?

Or is there a way to tell which specific row has been altered, after the fact?

Solution

  • The only way I can find to achieve this is to request the Primary Key(s) using Event::addEventColumn() along with the column you are listening for an event on. Then you can perform your own filtering based on that/those primary keys

    https://dev.mysql.com/doc/ndbapi/en/ndb-event-methods.html#ndb-event-addeventcolumn