Rails + MongoID - Querying by attribute

Question

I have a model like this:

class Lesson
  include Mongoid::Document

  field :title, :type => String
  field :category, :type => String
  field :price, :type => Float
  field :description, :type => String
  field :user_id, :type => String


  validates_presence_of :title
  validates_presence_of :category
  validates_presence_of :price
  validates_presence_of :user_id

  attr_accessible :title, :category, :description, :price

end

And I am trying to query like this:

@lessons_by_user = Lesson.find_by_user_id current_user.id

And I am getting:

undefined method `find_by_user_id' for Lesson:Class

How can I query by a specific attribute in MongoID?

I know how to do it like this:

@lessons = Lesson.all(:conditions=>{:user_id=>current_user.id.to_s})

but I am wondering if there is a shortcut...

Spone · Accepted Answer · 2014-01-25 17:48:43Z

12

Mongoid doesn't have the ActiveRecord style auto-created finder methods, it only supports a limited set of predefined finder methods:

Model.all
Model.count
Model.exists?
Model.find
Model.find_or_create_by
Model.find_or_initialize_by
Model.first
Model.last

However, it does have a general purpose where method so you say this:

@lessons = Lesson.where(:user_id => current_user.id)

where is chainable as well (just like where in newer versions of ActiveRecord) so you can add more conditions or specify the ordering by chaining more criteria calls.

edited Jan 25, 2014 at 17:48

Spone

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answered Mar 17, 2012 at 4:50

mu is too short

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Spone · Accepted Answer · 2014-01-26 11:36:26Z

3

Since the version 3.0.0 of Mongoid, you can also do:

@lessons = Lesson.find_by(user_id: current_user.id)

Contrary to where, it will raise a Mongoid::Errors::DocumentNotFound exception if the request returns no result. It's the default behavior, but if you set the raise_not_found_error configuration option to false, it will just return nil in this case.

Source: http://mongoid.org/en/mongoid/docs/querying.html

edited Jan 26, 2014 at 11:36

answered Jan 25, 2014 at 17:38

Spone

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1 Comment

mu is too short Over a year ago

Thanks for the "2 vs 3" doc fixes above. Even AR is moving towards find_by instead of all that nasty find_by_user_id stuff in method_missing.

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