Associations versioning

Logidze has a feature of associations versioning. The best way to explain it is by the example:

class Post < ActiveRecord::Base
  has_many :comments
  has_logidze
end

class Comment < ActiveRecord::Base
  belongs_to :post
  has_logidze
end

# 2017-01-19
post = Post.create!(post_params)

# 2017-01-22
comment = post.comments.create(body: 'My comment')

# 2017-01-24
comment.update!(body: 'New text')

# at this time comment wasn't updated yet...
old_post = post.at('2017-01-23')

# ...so we see its original body, although post itself wasn't changed
old_post.comments.first.body #=> 'My comment'

# at this time post didn't have comments at all
very_old_post = post.at(time: '2017-01-20')
very_old_post.comments.length #=> 0

This feature is considered experimental, so it's disabled by default. You can turn it on by setting Logidze.associations_versioning to true. Associations versioning works with belongs_to and has_many associations.

Limitations

• You could notice the usage of the length method instead of the size in the example above. Because ActiveRecord fires SQL COUNT request in the size, if association wasn't loaded in memory, it bypasses logidze, and returns a not versioned result. The length, in turn, always loads association at first, so we can apply versioning here
• The empty?, any?, many?, blank? methods will always load association in memory. So the collection_ids does too
• Persisting methods, such as update_all, collection_ids= and etc., are left as they are, so they will change current associations records in the database, no history changing
• at! method doesn't take into account associations