Prevent deleting foreign key

rubyonrails-talk
1

I've a Report and ReportType. The Report has one ReportType. Now I want prevent deleting of used ReportTypes. This is my ReportType class:

class ReportType < ActiveRecord::Base validates_presence_of(:name); has_many :reports end

And my Report class:

class Report < ActiveRecord::Base belongs_to :report_type,             :class_name => "ReportType",             :foreign_key => "report_type_id" end

I can create a query to find related reports, but I don't think that's the right way. Can anyone help?

2

I can create a query to find related reports, but I don't think that's the right way. Can anyone help?

That would be one option. Do that in an before_destroy callback.

Option number two: use a counter_cache. Add a column report_count to ReportType and define

belongs_to :report_type,             :class_name => "ReportType",             :foreign_key => "report_type_id",            :counter_cache => true

Then, again in before_destroy you can check for the number of records without an extra query (and comes in useful in many other situations)

3

Then, again in before_destroy you can check for the number of records without an extra query (and comes in useful in many other situations)

But can I also place a restrict on delete in my database and catch that error?

4

Then, again in before_destroy you can check for the number of records without an extra query (and comes in useful in many other situations)

But can I also place a restrict on delete in my database and catch
that error?

Yes, create an actual foreign key constraint. rails won't help you
there, but you can execute arbitrary sql in your migrations (or
anywhere else in fact), so just lookup foreign keys in the
documentation of your database.

Fred