Support passing record to uniqueness validator's :conditions option

[eliotsykes]

Support passing record to uniqueness validator's :conditions option.

This allows building conditions based on the record's attributes.

E.g. To validate slug must be unique for the day of publication:

class Article < ApplicationRecord

  validates_uniqueness_of :slug,
    conditions: ->(record) {
      where(published_at: record.published_at.beginning_of_day..record.published_at.end_of_day)
    }

If this is a welcome addition, please say and I'll refine this and add test coverage.

[p8]

Hi @eliotsykes.
To ensure uniqueness you probably also want a unique index in the database.
The Article example could also be solved by adding an extra column for the published_at date (without the time).

validates_uniqueness_of :slug, { scope: :published_at_date }

[eliotsykes]

Thanks @p8, these techniques are in use but not entirely desirable for this particular project.

If this enhancement is a welcome addition, please say and I'll refine this and add test coverage.

[rails-bot]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
Thank you for your contributions.

[eugeneius]

This seems like a useful feature, analogous to how association scopes can access the record.

The example in the description could be properly backed by an expression index.

[eugeneius]

Can you add a changelog entry and squash your commits?

[eugeneius]

Since options[:conditions] can only be a callable, I think we should skip the indirection via Relation#merge and call instance_exec here directly, so it's more obvious how this branch differs from the one below:

Suggested change

	relation.merge(conditions)
	relation.instance_exec(&conditions)

[eugeneius]

This example should be incorporated into the API documentation instead, probably here.

[eugeneius]

RuboCop is complaining because this variable is assigned but unused.

If you want to keep it as documentation, you'll need to add a leading underscore:

Suggested change

	todays_topic = Topic.create!(title: "Highlights of the Day", written_on: today_midday)
	_todays_topic = Topic.create!(title: "Highlights of the Day", written_on: today_midday)

[eliotsykes]

Thanks for the feedback @eugeneius, I think this is ready now.

[eugeneius]

Thank you @eliotsykes! 🙌

[hpjaj]

Nice work @eliotsykes ! 👏 👏