Count method

[davydovanton]

I think it will be awesome to create COUNT command for repository object. What do you think?
If you agree I can send PR 😊

[mereghost]

Not sure if I follow the reasoning. ROM already provides a #count method. Keeping it private to the repository would remain consistent (besides I rarely needed a count without either a filter or an aggregation, but YMMV).

[davydovanton]

/cc @hanami/core-team, @hanami/contributors, @solnic and @flash-gordon

[davydovanton]

After a little discussion with @flash-gordon I want to update my point of view.

Of course I can call count method from rom relation object like this UserRepo.new.users.count. But I think it looks strange in hamani model. That's why I suggest adding count alias like where, find and create. And after that, it'll look like more understandable like UserRepo.new.count

[beauby]

@davydovanton Note that in the latest version of hanami-model there is no publicly available #where method.
In your suggestion, your count method would only return the count of all users, without scoping, right? If so, it would have little use IMO (since you can't combine it with where from the outside).

[davydovanton]

@beauby yep, I think that #count should return only integer value

[beauby]

@davydovanton Right. What I meant was more: would you expect this Hanami::Repository#count method to take parameters?

[davydovanton]

@beauby good question. I can't answer this question. Now I want to see a simple implementation of #count method. Without params. But maybe someone wants to see something like rails #count with conditions and etc.

[beauby]

@davydovanton That's what I thought. The philosophy of the new hanami-model, though, is to not expose such query methods externally, and instead have you define intent-stating methods.

[flash-gordon]

It probably can be done via blocks, like repo.count { active } so you can't detach a query object from a repo.

[jodosha]

Please cast your vote here. What do you think about this feature?

It would be:

class BookRepository < Hanami::Repository
  def on_sale
    books.where(on_sale: true)
  end
end

repository = BookRepository.new
repository.count # => 100
repository.on_sale.count # => 12

[davydovanton]

@jodosha awesome 👍

[beauby]

So basically it's an ActiveRecord scope? Because then you could do BookRepository.new.where(foo: :bar).combine(...).limit(5) BookRepository.new.on_sale.where(foo: :bar).combine(...).limit(5).

Basically, either you need the records, and you get no penalty from materializing the collection, or you don't need the records, and you might as well define an actual repository method for getting the count.

[solnic]

@beauby relation API is not exposed via repos so it'd be something like repo.books.where(...).count

[solnic]

FWIW I don't think repos should expose such a db-specific API as count. If you need this, just reach to a specific relation, ie repo.books.count. Having a Repo#count would be super hard to implement if it was supposed to work with any adapter.

[beauby]

@solnic My bad, I edited my answer (forgot the .on_sale method, to build upon @jodosha's example).

[jodosha]

Having a Repo#count would be super hard to implement if it was supposed to work with any adapter.

I forgot about this aspect, thank you @solnic to reminding us.

---

Folks, I think this changes the direction of this discussion. We can't have #count as part of the public interface of Hanami::Repository, because count logic isn't necessary implemented by the underlying ROM adapter (and database).

[jodosha]

Folks, I've implemented a proposal at #354, can you please have a look? Thanks.

[jodosha]

Now that we have a more clear picture of both the implications and the solutions, I think we can close this.

---

"Count" is a concept not generally available to all the databases. SQL databases have it, but others don't.

If you're using a SQL database you can expose a method for that.

class BookRepository < Hanami::Repository
  def count
    books.count
  end
end

If you want to count the records, under specific conditions:

class BookRepository < Hanami::Repository
  # ...

  def on_sale_count
    books.where(on_sale: true).count
  end
end

If you want to use raw SQL you can do:

class BookRepository < Hanami::Repository
  # ...

  def old_books_count
    books.read("SELECT id FROM books WHERE created_at < (NOW() - 1 * interval '1 year')").count
  end
end

We should document this. I'm gonna create an issue over our website repository.

[jackbit]

wisely it should be external plugin / gem and not in core modules. It is classic issue in ActiveRecord at beginning and till now, we can not combine mongoose, mongoid, oracle or any else into the same active record, the solution is remove active record and use external plugin or create an enhanced adapter. It should be the same game for hanami.