Question

Yes, I know how to create many to many relationships but nothing else. I did a google search and read official mongoid documentation but I didn’t anything about how to work with it. By work I mean inserting, updating, deleting, finding, counting…

For example, suppose I have 2 models (from documentation):

class Band
  include Mongoid::Document
  has_and_belongs_to_many :tags
end

class Tag
  include Mongoid::Document
  field :name, type: String
  has_and_belongs_to_many :bands
end

What should I do to make all the operations I mentioned above?

P.S. I use Sinatra and mongoid 3.

Answer 1

Inserting

From the documentation table immediately following your sample models (plus my comment).

# Create a tag for a band
band.tags.create(name: "electro")

Finding

Also from the same table.

# Find a tag that belongs to that band, whose name is "electro"
tag = band.tags.where(name: "electro") 

Updating

From the doc on persistence, modified for the band/tags example.

# using variable tag from previous line.
tag.update_attributes(name: "dubstep")

Counting

From the doc on querying, which also contains information useful for the other items here (also modified).

band.tags.length

Deleting

This is from the persistence document also.

# we will delete the tag from earlier
tag.delete

Lastly

All the information needed to work Mongoid is in the docs, which are actually very thorough and useful. There is definitely a lot, but you can make it through it in a couple hours.