Document lack of uniqueness validation

[xruins]

Even validate: true was set for import method,
ActiveRecord::Validations::UniquenessValidator will be disabled by the code on https://github.com/zdennis/activerecord-import/blob/master/lib/activerecord-import/import.rb#L42 .

Since it's confusable without an annotation, I prefer this incompatibility is mentioned in some document.

[jkowens]

Good idea. The history of why uniqueness validation is avoided is found here: #228.

[xruins]

Thanks! :)

[jkowens]

An option validate_uniqueness has been added in v0.27.0 that allows users to enable uniqueness validation:

Book.import books, validate_uniqueness: true

This is not a recommended approach as it has several potential issues, so user beware ☠️

[dillonwelch]

It seems like instead of adding documentation around an option that doesn't do anything, the better approach would be to get rid of the option?

[jkowens]

@oniofchaos we had completely removed uniqueness validation, but with v0.27.0 we added an option to enable it. By default validating an import will not validate uniqueness. The option validate_uniqueness must be set to true for it to happen. So that's really what needs documented now, the default behavior and the special option.

[xruins]

Thanks a lot!

[khalilgharbaoui]

I know this issue is closed but there is an unanswered question here:

does validate_uniqueness: true work independently from validate: true?

If yes maybe we need it in the docs if no we also need it in the docs
This is otherwise confusing and a pain even on and beyond 04-12-2019