Re: Good database design -- multiple databases in one app??

As I think about it, putting comma-delimited data in one field is
pretty yucky.... i suppose there could be an extra table called
undo_fields which has a foreign key to the undo table.

On Apr 25, 3:20 am, Zaky Katalan-Ezra <procsh...@gmail.com> wrote:
> About the auto increment I meant the mysql column property AI.
>
> About undo:
> In that case if you don't save your sessions to table and the session is
> lost it's impossible to undo.
>
> Usually undo implemented with the state pattern.
>
> But in your case , I'll recommend keeping the initial data locally or to
> undo table  that will hold update statements.
>
> 1. undo table:
> table_name
> row_id
> update_statement
>
> 2.Before editing a table1 create an update statement for each row and insert
> it to the update table.
> insert into undo ('table1',1,'update table table1 set col1= 'old_val', ....
> where id = 1' );
>
> 3.update the table1
> 4. undo
>    a) select id from table 1 where id not in (select row_id from undo where
> table_name = 'table1' )
>        delete all the rows you get, these are all new rows.
>     b) run all update  statements from undo table
>         If you get an error  change the update statement to insert
> statement, the user probably delete this row.
> 5. delete from undo where table_name = 'table1';
>
> If you add user id to this process each user will be able to undo only his
> changes.
>
> I think its better to implement it with before update, after insert and
> before delete mysql  triggers.
> This way you save only changed rows.
>
> Its just a sketch so don't take it as it is, think it over
>
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>
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