Question

I have an existing application (with MySQL DB).

I just got a new requirement where I need to delete some records from one of main entity. I dont want to apply hard delete here as its risky for whole application. If I use soft delete I have to add another field is_deleted and because of that i have to update all my queries (like where is_deleted = ‘0’).

Please let me know if there is any smarter way to handle this situation. I have to make changes in half of the queries if I introduce a new flag to handle deletes.

Answer 1

Your application can run without any changes. MySQL is ANSI-SPARC Architecture compliant . With external schema you achieve codd’s rule 9 “Logical data independence”:

Changes to the logical level (tables, columns, rows, and so on) must
not require a change to an application based on the structure. Logical
data independence is more difficult to achieve than physical data
independence.

You can rename your tables and create views with original table names. A sample:

Let’s supose a table named my_data:

REMAME TABLE my_data TO my_data_flagged

ALTER TABLE my_data_flagged 
   ADD COLUMN is_deleted boolean NOT NULL default 0;

CREATE VIEW my_data AS 
   SELECT * 
   FROM my_data_flagged 
   WHERE  is_deleted = '0'

Another way is create a trigger and make a copy of erased rows in independent table.