CODEWITHSUNDEEP
mongodbmongoid
Vasia Pupkin
Vasia Pupkin

Reputation: 223

Mongoid: relations between embedded documents

I have two collections in my DB-

> db.users.find().pretty()
        {
            "_id" : ObjectId("5281c15a617274166f150000"),
            "email" : "[email protected]",
            "nickname" : "Artem",
            "user_activities" : [
                {
                    "_id" : ObjectId("5281c19161727415d5000000"),
                    "activity_id" : ObjectId("5281c15a617274166f010000"),
                    ...
                },
                {
                    "_id" : ObjectId("5281c19161727415d6000000"),
                    "activity_id" : ObjectId("5281c15a617274166f020000"),
                    ...
                },
                       ...
            ]
        },
       ....

and 

> db.monitor_symptoms.find().pretty()
    {
        "_id" : ObjectId("5281c15a617274166f000000"),
        "activities" : [
            {
                "_id" : ObjectId("5281c15a617274166f010000"),
                "name" : "ASW"
                        ...
                },
                {
                "_id" : ObjectId("5281c15a617274166f010000"),
                "name" : "BSW"
                        ...
                },
                ...
       ],
       ...
    },
    ...

This is supported by the following models in my app-

class User
  include Mongoid::Document
  field :email, type: String, :default => ""
  field :nickname, type: String, :default => ""
  embeds_many :user_activities
end

class UserActivity
  include Mongoid::Document
  embedded_in :user
  has_to_many :activities, inverse_of: nil
end

class MonitorSymptom
  include Mongoid::Document
  embeds_many :activities
end

class Activity
  include Mongoid::Document
  field :name, type: String
  embedded_in :monitor_symptom
end

I try next-

2.0.0p0 :090 >   user = User.first
 => #<User _id: 5281c15a617274166f150000, email: "[email protected]", nickname: "Artem"

2.0.0p0 :091 > user.user_activities.new(activity_id: "5281c15a617274166f010000")
 => #<UserActivity _id: 5281c15a617274166f150000, activity_id: "5281c15a617274166f010000"> 

2.0.0p0 :092 > user.save

And I catch an error:

Mongoid::Errors::MixedRelations: Problem: Referencing a(n) Activity document from the UserActivity document via a relational association is not allowed since the Activity is embedded. Summary: In order to properly access a(n) Activity from UserActivity the reference would need to go through the root document of Activity. In a simple case this would require Mongoid to store an extra foreign key for the root, in more complex cases where Activity is multiple levels deep a key would need to be stored for each parent up the hierarchy. Resolution: Consider not embedding Activity, or do the key storage and access in a custom manner in the application code.

Please help me to make this reference.

Upvotes: 1

Views: 314

Answers (1)

abhas
abhas

Reputation: 5213

The model which is embedded_in some other model can't have relationships other than embed...for your case activity is embedded in monitor_symptom it can't be refrenced from other document(hich you are doing in user_activity). When you have such a complex structure, it is better to use refrenced relationship between document rather than embed. For e.g. in between user and user_activity, monitor_symptom and activity then you can easily have refrenced relationship between activity and user_activity.

Upvotes: 2

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