Associations (one-to-many, many-to-one)

[hlegius]

/cc @Heruku

I've copied #56 from heruku and started to grow the association .preload idea (started by him) to get it working properly.
First, I tried to fork heruku's PR and rebase from there, but I've got no success on it due tons of new features which has been added since them. So, I decided to fork Lotus' repo, get diff from #56 and reapply file by file, paying attention to each new detail.

Todo:

• Associations within queries, i.e:

class ArticlesRepository
  def self.by_category(category)
    query.where(category_id: category.id).preload(:category)
  end

  def with_category
    query.preload(:category)
  end

  def published
    query.where(published: true)
  end
end

flower = CategoryRepository.find_by_name('Flowers') # <= Category Object
article = ArticlesRepository.by_category(flower).first # or all, or last, etc.
article # <= Article Object
article.category_id # <= Integer (category_id field)
article.category # <= Category Entity (same as flower var)

• Associations with queries, i.e. ArticlesRepository.with_category.published.all

article = ArticlesRepository.with_category.published.first # or all, or last, etc.
article # <= Article Object
article.category_id # <= Integer
article.category # <= Category Entity

• Associations with preload at the end of sentence, i.e. ArticlesRepository.published.with_category.all

article = ArticlesRepository.published.with_category.first # or all, or last, etc.
article.category # <= Category Entity

Known Limitations (so far)

# any Adapter
flower = CategoryRepository.find_by_name('Flowers')
article = ArticlesRepository.with_category.by_category(flower).first
article.category.articles # nil
# I have some ideas here, but need to chat with you guys before :]

# Memory Adapter

article = ArticlesRepository.published.with_category.first # or all, or last, etc.
# Error: Method `.with_category` not found

# but, single query wrapped inside Repository will work fine

article = ArticlesRepository.by_category(category).first # or all, or last, etc.
article.category # <= Category object

Also, refers to #35

[AlfonsoUceda]

@hlegius nice job, and thanks to @Heruku too, would you like to create a test for one_to_many file? because there is one for test/model/associations/many_to_one_test.rb

[AlfonsoUceda]

I think this example should be User instead [User]because we have a singular association

[hlegius]

@AlfonsoUceda no problems. Thanks for review'ng. I'm gonna take a look at it and create the missing test as well.

[AlfonsoUceda]

what do you think to add splat operator? I think is better this api
preload(:users, :articles) than preload(:users).preload(:articles)

def preload(*associations)
  associations.each do |association|
    @associations << association
  end
end

cc @lotus/core-team

[hlegius]

Personally I prefer your version, but I'd rather don't break the Query's where api contract i.e query.where(foo: :baz).where(baz: :qux). If it isn't a "problem", then I can change, no problems!

[andresilveirah]

Hey @hlegius nice work! @AlfonsoUceda is there anything impeding this PR to be merged? Anything I can do? I'm currently implementing an example of Association with Lotus and it would be awesome to have this feature.

[jodosha]

@hlegius This is a great work! 👏

What prevents us to merge this is the lack of implementation of the other half of the job: writing associated entities. Please have a look at this gist: https://gist.github.com/jodosha/431091eebb41606b358a

/cc @lotus/core-team @andresilveira

[hlegius]

@jodosha is there anything that I can do to help this feature get merged? I mean, what's your plans to do before merge it? maybe I could help o/

/cc @AlfonsoUceda

[qcam]

Looking forward to this!!! 👍

[jodosha]

@hlegius Mr @joneslee85 (PING) will help you to finalize this. 😸

[runlevel5]

@hlegius polite ping from me, grab me and we work this out together

[hlegius]

@jodosha do you think it still will be useful somehow? If yes, @joneslee85 can I ping you on Gitter to talk about schedule/tasks to do?

[jodosha]

@hlegius @joneslee85 Please hold on until we'll release 0.6

[regishideki]

I think description should be 'defines a one to many association'