seemingly complex ActiveRecord associations problem

rubyonrails-talk
1

Hi,

I want to specify relationships between two classes like that expressed in the following pseudocode:

class User < ActiveRecord::Base    has_many :projects end

class Project < ActiveRecord::Base

has_one :primary_record_owner, :<pseudo_option_for_referring_to>=>"User"    has_many :record_owners, :<pseudo_option_for_referring_to>=>"User"    has_many :users # this refers to User, too end

From the above I seek the following kind of results:

@user.projects # returns all projects associated with the user from any of the three User associations in Project @project.primary_record_owner # returns the User instance @project.record_owners # returns the collection of User instances @project.users # returns User instances, not necessarily overlapping with the other associations

The intent I mean to express is that a Project can have any of three levels of relationship with a User, while a User has only one level of association with a Project.

I was thinking HABTM, but I don't see how to get my desired '@user.projects' result from that.

Any helpful comment would be greatly appreciated.

Thanks,

Lille

2

I’m thinking about 4 models

  • User
  • Project
  • RecordOwner
  • UserProject → this is the join table for user and project You won’t need RecordOwner if record_owners is a subset of the users association.

Give us an example so we can help out with the options you want.

3

Jim,

Thanks, but your proposed RecordOwner would have no behavior distinct from User and would not describe the relationship from the Project model's perspective. My User shouldn't care about the kind of relation it has to Project, rather the reverse.

My pseudocode is about as specific as I know how to get.

To recap in its most distilled form, my problem is what relationships to include in two models, User and Project, where a User may be associated with Project in any of three ways -- User, 'primary_record_owner', or 'record_owner, such that the following expressions are possible:

1) @user.projects # returns all projects associated with a User instance 2) @project.primary_record_owner # returns a User instance 3) @project.record_owners # returns a collection of User instances 4) @project.users # returns a collection of User instances

I think I see how to accomplish 2-4, using HABTM, but I don't see how to accomplish 1) at the same time.

Thanks,

Lille

4

Jim,

Thanks, but your proposed RecordOwner would have no behavior distinct from User and would not describe the relationship from the Project model's perspective. My User shouldn't care about the kind of relation it has to Project, rather the reverse.

My pseudocode is about as specific as I know how to get.

To recap in its most distilled form, my problem is what relationships to include in two models, User and Project, where a User may be associated with Project in any of three ways -- User, 'primary_record_owner', or 'record_owner, such that the following expressions are possible:

1) @user.projects # returns all projects associated with a User instance 2) @project.primary_record_owner # returns a User instance 3) @project.record_owners # returns a collection of User instances 4) @project.users # returns a collection of User instances

I think I see how to accomplish 2-4, using HABTM, but I don't see how to accomplish 1) at the same time.

Have you thought about a polymorphic join model between the two, like maybe a Role? That's how I ended up structuring a recent project.

Walter

5

Walter,

Yes, Role sounds promising. If it's not too much to ask, could you please paste some of what you ended up with?

Lille

6

Sure. Strictly speaking, what I ended up with was not polymorphic, but it suited my project all right. Polymorphic is the fully buzzword-compliant way to go here, because it would let you have different validations for each user type, etc.

class Role < ActiveRecord::Base    belongs_to :campaign    belongs_to :user    has_many :approvals, :dependent => :destroy    validates_presence_of :user_id, :on => :create, :message => "can't be 0"    validates_presence_of :role_name, :on => :create, :message => "can't be blank"    # ... end

class User < ActiveRecord::Base    devise :database_authenticatable, :recoverable, :rememberable, :trackable, :validatable, :invitable    has_many :notes, :dependent => :destroy    has_many :roles, :dependent => :destroy    has_many :campaigns, :through => :roles    default_scope :order => 'name'    validates_presence_of :name, :on => :update, :message => "can't be blank"    attr_accessible :email, :password, :password_confirmation, :name, :initials    # ... end

class Campaign < ActiveRecord::Base    has_attached_file :header, :styles => {}    attr_accessible :name, :campaign_date, :header, :header_fill_color, :page_fill_color    has_many :roles, :order => "position ASC", :dependent => :destroy    has_many :users, :through => :roles    default_scope :order => 'position'    # ... end

This was Rails 2.3.10, in case that matters to you.

Walter

7

Jim,

Thanks, but your proposed RecordOwner would have no behavior distinct

from User and would not describe the relationship from the Project

model’s perspective. My User shouldn’t care about the kind of relation

it has to Project, rather the reverse.

My pseudocode is about as specific as I know how to get.

To recap in its most distilled form, my problem is what relationships

to include in two models, User and Project, where a User may be

associated with Project in any of three ways – User,

‘primary_record_owner’, or 'record_owner, such that the following

expressions are possible:

  1. @user.projects # returns all projects associated with a User

instance

Can’t you use a condition for the has many while eager loading the other models? Something like

has_many :projects, :include => [:record_owners, :project_users], :include => ‘primary_record_owner = #{self.id} OR record_owners.user_id = #{self.id} OR project_users.user_id = #{self.id}’

8

Guys,

Good stuff.

@Walter - what bothers me about the Role approach is that I will need to write accessor methods on Project -- #primary_record_owner, #record_owners -- to retrieve the desired Role players by finding on attributes like is_record_owner or is_primary_record_owner in Role.

That's not too great a burden, but...

@Jim - maybe I can get what I need from something along the lines of the following?

class Project < ActiveRecord::Base   has_one :primary_record_owner ... # see discussion farther below...   has_and_belongs_to_many :record_owners, :class_name => "User", :join_table => :projects_record_owners   has_and_belongs_to_many :users, :join_table => :projects_users end

class User < ActiveRecord::Base    has_many :projects, :include => [:record_owners, :users, :primary_record_owner], :include => 'primary_record_owner = #{self.id} OR record_owners.user_id = #{self.id} OR project_users.user_id = #{self.id}' end

I'm in over head...I think this dead-ends in at least one place, with the has_one association in Project. Seems like I would have to describe that as a has_one :through association.

Lille

9

This seems like a good place to use a decorated join model with has_many :through. Code:

class User < AR::Base   has_many :project_links   has_many :projects, :through => :project_links end

class ProjectLink < AR::Base   belongs_to :user   belongs_to :project   # other fields here:   # primary: boolean, default false   # owner: boolean, default false end

class Project < AR::Base   has_many :project_links

  has_many :users, :through => :project_links, :conditions => { :project_links => { :owner => false } }   has_many :record_owners, :through => :project_links, :source => :user, :conditions => { :project_links => { :owner => true, :primary => false } }   has_one :primary_owner, :through => :project_links, :source => :user, :conditions => { :project_links => { :owner => true, :primary => true } } end

You'll probably need some callbacks to handle the "only one primary owner" restriction, but everything else should work as written.

--Matt Jones