Columns filtering

[palkan]

What

We need a way to restrict versioning to a subset of columns.
These can be done in 2 ways: through whitelisting and blacklisting.

Why

To reduce the size of the log data.

How

Extend logidze_logger function (and related functions) to support 2 more arguments, except and only. Then CREATE TRIGGER migration looks like:

execute <<-SQL
  CREATE TRIGGER logidze_on_users
  BEFORE UPDATE OR INSERT ON users FOR EACH ROW
  WHEN (current_setting('logidze.disabled') <> 'on')
  EXECUTE PROCEDURE logidze_logger(null, null, '{name, role, email, phone}');
SQL

Where the first argument is a limit (as it is now), the second argument is a blacklist of columns, and the third argument is a whitelist of columns.

We should be able to specify these parameters through generator script:

rails generate logidze:model Post --only="title,user_id,tags"

rails generate logidze:model Post --except="created_at,updated_at"

We also need a way to upgrade existing triggers (maybe through the --upgrade flag).

[smaximov]

Are --only and --except options mutually exclusive? If they are, wouldn't it be more convenient to have logidze_logger take a list of columns as the second argument and a boolean flag indicating the type of the filter (i.e., blacklist or whitelist)?

[palkan]

Yes, they are exclusive.
And "yes" again: then boolean flag make sense.