I have a many-to-many association between a Post and a Tag model:
post.rb:
has_many :taggings, dependent: :destroy
has_many :tags, through: :taggings
tag.rb:
has_many :taggings, :dependent => :destroy
has_many :posts, :through => :taggings
tagging:
attr_accessible :tag_id, :post_id
belongs_to :post
belongs_to :tag
I want to have a page where I list all the tags and how many posts each tag has.
So I added a posts_count column to tags:
create_table "tags", :force => true do |t|
t.string "name"
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
t.integer "posts_count", :default => 0, :null => false
end
I've used counter cache before:
reply.rb:
belongs_to :post, :counter_cache => true
But I'm not sure how to do it with this many-to-many association. Any ideas?
Use common :counter_cache option for tags. Despite the fact that it counts Taggings objects, which belongs_to (just one) post, this is what you looking for.
# tagging:
attr_accessible :tag_id, :post_id
belongs_to :post
belongs_to :tag, :counter_cache => :posts_count
validates_uniqueness_of :tag_id, :scope => :post_id
Validator will prevent the creation of several identical tags for the same posts, thus you can avoid duplicate records.
Related
I am trying to save a person's Facebook friends into my database. I want to store the Facebook users in a table and then store their friendships in another table. The friendships would have the integer of the FacebookUser that requested the friendship and the integer of the friend, both of which are foreign keys to the facebook_users table. However I keep getting this message when I try to link the a user's facebook friends with friendships.
Error
ActiveRecord::HasManyThroughSourceAssociationNotFoundError: Could not find the source association(s) :friend or :friends in model Friendship. Try 'has_many :friends, :through => :friendships, :source
=> <name>'. Is it one of :FacebookUser or :FacebookFriend?
friendship.rb
class Friendship < ActiveRecord::Base
attr_accessible :facebook_user_id, :facebook_friend_id
belongs_to :FacebookUser
belongs_to :FacebookFriend, :class_name => :FacebookUser
end
facebook_user.rb
class FacebookUser < ActiveRecord::Base
attr_accessible :first_name, :gender, :last_name
has_many :friendships, :foreign_key => :facebook_user_id
has_many :friends, :through => :friendships, :source => :FacebookUser
end
Schema
create_table "facebook_users", :force => true do |t|
t.string "first_name"
t.string "last_name"
t.string "gender"
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
end
create_table "friendships", :force => true do |t|
t.integer "facebook_user_id"
t.integer "facebook_friend_id"
end
the convention Rails uses is to use associations as defined by the class name and the foreign key. if you've set up your tables like above, you should change your models to the following.
class Friendship < ActiveRecord::Base
attr_accessible :facebook_user_id, :facebook_friend_id
belongs_to :facebook_user # implies a foreign key of facebook_user_id and class of FacebookUser
belongs_to :facebook_friend, class_name: 'FacebookUser' #implies a foreign key of facebook_friend_id
end
class FacebookUser < ActiveRecord::Base
attr_accessible :first_name, :gender, :last_name
has_many :friendships
has_many :friends, :through => :friendships, :source => :facebook_friend
end
I've read lots about self referential classes in Rails, but am still having problems getting them working.
I have a class of Articles and I want them to be able to refer to each other, from a source article to an outcome article - and then be able to find the reverse. So I'm trying to do a has_many through, using another class called Links.
My schema is
create_table "articles", :force => true do |t|
t.string "name"
t.text "body"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "links", :force => true do |t|
t.integer "source_id"
t.integer "outcome_id"
t.string "question"
t.datetime "created_at"
t.datetime "updated_at"
end
The models are
class Article < ActiveRecord::Base
has_many :links_as_source, :foreign_key => "source_id", :class_name => "Link"
has_many :sources, :through => :links_as_source
has_many :links_as_outcome, :foreign_key => "outcome_id", :class_name => "Link"
has_many :outcomes, :through => :links_as_outcome
end
and
class Link < ActiveRecord::Base
belongs_to :source, :foreign_key => "source_id", :class_name => "Article"
belongs_to :outcome, :foreign_key => "outcome_id", :class_name => "Article"
end
I can create articles in the console, and I can link articles together, using a.outcomes << b but the link table is only storing the outcome_id, not the source_id.
What am I doing wrong?
I got this to work in the end. I changed the names - I don't know if that mattered. I did read somewhere that source was a silly name to use for something.
So this is what works:
My schema
create_table "article_relationships", :force => true do |t|
t.integer "parent_id"
t.integer "child_id"
...
end
create_table "articles", :force => true do |t|
t.string "name"
...
end
My article model
has_many :parent_child_relationships,
:class_name => "ArticleRelationship",
:foreign_key => :child_id,
:dependent => :destroy
has_many :parents,
:through => :parent_child_relationships,
:source => :parent
has_many :child_parent_relationships,
:class_name => "ArticleRelationship",
:foreign_key => :parent_id,
:dependent => :destroy
has_many :children,
:through => :child_parent_relationships,
:source => :child
After reading the Ruby on Rails guides and a few of the stackoverflow responses to questions about polymorphic association I understand its use and implementation but I have a question about a specific use scenario. I have tags that can be associated with multiple topics, categories, images and other various models (which also have varying tags) but instead of placing the reference fields (foreign_id, foreign_type) within the tags table, I'd prefer to create a separate association table. Is this still possible using :polymorphic => true?
Something like this:
create_table :tags do |t|
t.string :name
t.remove_timestamps
end
create_table :object_tags, :id => false do |t|
t.integer :tag_id
t.references :tagable, :polymorphic => true
t.remove_timestamps
end
If this isn't possible, I was planning on creating the same :object_tags table and using :conditions within the Tag model and other models to force the associations. Is there a rails way of doing this? Thanks! (working with rails 3.0.9 & ruby 1.8.7 <- because deployment server is still using 1.8.7)
UPDATE:
Thanks Delba! Answer is a working solution for HABTM polymorphism.
class Tag < ActiveRecord::Base
has_many :labels
end
class Label < ActiveRecord::Base
belongs_to :taggable, :polymorphic => true
belongs_to :tag
end
class Topic < ActiveRecord::Base
has_many :labels, :as => :taggable
has_many :tags, :through => :labels
end
create_table :tags, :timestamps => false do |t|
t.string :name
end
create_table :labels, :timestamps => false, :id => false do |t|
t.integer :tag_id
t.references :taggable, :polymorphic => true
end
UPDATE: Because I need bi-directional HABTM, I ended up going back to creating individual tables.
Yes, and from your description you couldn't have the tagable columns on your tag anyhow since they can have multiple tagable things and vice versa . You mentioned HABT, but you can't do anything like has_and_belongs_to, :polymorphic => true as far as I know.
create_table :object_tags, :id => false do |t|
t.integer :tag_id
t.integer :tagable_id
t.string :tagable_type
end
Your other tables don't need any columns for object_tags, tags, or tagable.
class Tag < ActiveRecord::Base
has_many :object_tags
end
class ObjectTag < ActiveRecord::Base
belongs_to :tagable, :polymorphic => true
belongs_to :tag
end
class Topic < ActiveRecord::Base
has_many :object_tags, :as => :tagable
has_many :tags, :through => :object_tags
end
In my Rails 3 project, I have a user model with a self referential join, through the follow model. I want to use this join table to find activity related to the followed user. I have almost everything set up correctly, except that the query generated by the join is totally ignoring the :primary_key option on the join model.
Here is the relevant schema for the relevant models:
create_table "users", :force => true do |t|
t.string "email", :default => "", :null => false
t.string "first_name"
t.string "last_name"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "follows", :force => true do |t|
t.integer "user_id"
t.integer "followed_user_id"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "activities", :force => true do |t|
t.integer "user_id"
t.text "body"
t.datetime "created_at"
t.datetime "updated_at"
end
Here's the associations in the models
class User < ActiveRecord::Base
has_many :follows
has_many :followed_users, :through => :follows
has_many :followed_activities, :through => :follows
has_many :activities
end
class Follow < ActiveRecord::Base
belongs_to :user
belongs_to :followed_user, :class_name => "User"
has_many :followed_activities, :primary_key => :followed_user, :foreign_key => :user_id, :class_name => "Activity"
end
The following work just fine:
u = User.first
u.follows # returns corresponding records from the follows table
u.followed_users # returns all users that u is following
u.followed_users.first.activities # returns all activity records corresponding to the first person the user is following
Follow.first.activities # same as the previous
However, the following just returns an empty array:
u.followed_activities
Here is the sql that is generated from the last statement:
Activity Load (0.2ms) SELECT `activities`.* FROM `activities` INNER JOIN `follows` ON `activities`.user_id = `follows`.id WHERE ((`follows`.user_id = 1))
The reason it isn't working is because it is trying to join use 'follows'.id as the primary key rather than 'follows'.followed_user.
Is this a bug, or do I have to repeat the :primary_key declaration somewhere on the user model? I can't find any mention anywhere in the Rails api, or anywhere else online.
Rails Version: 3.0.7
I've found it intuitive to daisy chain relationships with the 'nested_has_many_through' gem, http://rubygems.org/gems/nested_has_many_through which will be a standard part of rails 3.1 and could give you another tool to tackle the issue here
It will let you do something like this:
class Author < User
has_many :posts
has_many :categories, :through => :posts, :uniq => true
has_many :similar_posts, :through => :categories, :source => :posts
has_many :similar_authors, :through => :similar_posts, :source => :author, :uniq => true
has_many :posts_of_similar_authors, :through => :similar_authors, :source => :posts, :uniq => true
has_many :commenters, :through => :posts, :uniq => true
end
class Post < ActiveRecord::Base
belongs_to :author
belongs_to :category
has_many :comments
has_many :commenters, :through => :comments, :source => :user, :uniq => true
end
This has super-simplified my queries and collections. I hope you find an answer to your problem, it's a tough one!
Justin, you have 2 associations called "followed_activities". sure, they have different context (different models), but I'd like to ask you to try method inside the association block like this:
has_many :followed_users, :through => :follows do
def activities
end
end
I have a Comment class with a :foreign_key of post_id in the Post class.
class Comment < ActiveRecord::Base
belongs_to :post, :class_name => "Post", :foreign_key => "post_id", :counter_cache => true
belongs_to :author, :class_name => "User", :foreign_key => "author_id"
end
But my CreateComments migration does not define a database-level foreign key:
class CreateComments < ActiveRecord::Migration
def self.up
create_table :comments do |t|
t.column "post_id", :integer, :default => 0, :null => false
t.column "author", :string, :default => "", :limit => 25, :null => false
t.column "author_email", :string, :default => "", :limit => 50, :null => false
t.column "content", :text, :null => false
t.column "status", :string, :default => "", :limit => 25, :null => false
t.timestamps
end
end
def self.down
drop_table :comments
end
end
Instead post_id is a simple Integer column.
So, it seems that this foreign key relationship exists only in the mind of Rails, not at the database level.
Is this correct?
Also, is it necessary for the corresponding Post model to also declare its reciprocal foreign key relationship with Comments using the :foreign_key attribute or could that be omitted?
class Post < ActiveRecord::Base
set_table_name("blog_posts")
belongs_to :author, :class_name => "User", :foreign_key => 'author_id'
has_many :comments, :class_name => "Comment",
:foreign_key => 'post_id', :order => "created_at desc", :dependent => :destroy
has_many :categorizations
has_many :categories, :through => :categorizations
named_scope :recent, :order => "created_at desc", :limit => 5
end
The Rails default behaviour is that the column used to hold the foreign key on a model is the name of the association with the suffix _id added. The :foreign_key option lets you set the name of the foreign key directly. The associations between your Post and Comment model classes should look like this:
class Post < ActiveRecord::Base
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :post
end
—Note that you don't need :class_name => "Post" in your Comment model. Rails already has that information. You should only be specifying :class_name and :foreign_key when you need to override the Rails' conventions.
You're correct that Rails maintains the foreign key relationships for you. You can enforce them in the database layer if you want by adding foreign key constraints.
I think you would benefit from reading A Guide to ActiveRecord Associations.