I have Project has_many :locations and Locations has_many :comments, and Project has_many :plans and Plan has_many :comments. How do I select all the comments of all the commentable resources that belong to a project? I'm using ActiveAdmin and ActiveAdmin::Comment if that's relevant. What I've tried:
p = Project.first
comments = p.locations.map(&:comments).flatten + p.plans.map(&:comments).flatten
But is there an ActiveRecord or Rails way to do this? Or is there a SQL join that could do all that? Thanks!
if you make has_many location_comments through locations and the same for plans will be better. Also you can make model method like:
def all_comment
self.location_comments + self. plans_comments
end
Related
I have a sql-Statement and I'd like to "convert" it into rails (activerecord) method calls.
This is my query
'SELECT * FROM clients WHERE company_id IN (SELECT company_id FROM companies_projects WHERE project_id= ? )
companies_projects is a join table for an n:n relation of companies and projects
clients belong to companies (1:n)
project is an external resource and has no has_many companies, so I can't go from that direction
I want to get all clients that belong to companies that belong to one project, so I can list them in the index-page
My models
class Client < ActiveRecord::Base
belongs_to :company
end
class Company < ActiveRecord::Base
has_many :companies_projects
has_many :clients
has_many :projects, :through => :companies_projects
end
I checked the statement in rails console and it works.
I have two problems impelementing this query.
1. find_by_sql
I tried this method
Client.find_by_sql('SELECT * FROM clients WHERE company_id IN (SELECT company_id FROM companies_projects WHERE project_id= ? )',project.id)
But it throws an InvalidStatement Exception, MySQL Syntax Error near "?"
I also tried to put the sql and bindings into an array [sql,bind1], that works but I get an array and need an ActiveRecordRelation
2. where
I'm new to rails and can't figure out a valid method chain for such a query.
Could someone point me in the right direction?
I would prefer using ActiveRecord methods for the query, but I just don't know which methods to use for the nested selects.
You should have following associations between your models:
class Client < ActiveRecord::Base
belongs_to :company
end
class Company < ActiveRecord::Base
has_and_belongs_to_many :projects
has_many :clients
end
class Project < ActiveRecord::Base
has_and_belongs_to_many :companies
has_many :clients, through: :companies
end
Then it is simply:
project.clients
Client.where(company_id: CompanyProject.where(project_id: project.id).pluck(:id))
Or you can use JOIN
Client.joins(:company_project).where('companies_projects.project_id = ?', project.id)
But the best solution was proposed by #arup-rakshit
Considering that you have an intermediate model CompanyProject, this can be achieved with following query:
Client.where(:company_id => CompanyProject.where(:project_id => project_id).map(&:company_id) )
[Edit: made company_id a symbol)
I'm adding quiz functionality to the twitter app from the Hartl tutorial and have these Models:
User is nearly the same as the tutorial:
class User < ActiveRecord::Base
has_many :followed_users, through: :relationships, source: :followed
has_many :takens, dependent: :destroy
has_many :questions, through: :takens
end
Taken is a table of Question ids to User ids:
class Taken < ActiveRecord::Base
belongs_to :user
belongs_to :question
end
nothing interesting in Question:
class Question < ActiveRecord::Base
attr_accessible :category, :correct, :option1, :option2, :option3, :qn
end
I want to be able to show followed_users and followers in order of the number of tests they have taken. In the console this can be had through:
User.find_by_id(1).question_ids.count
Then I can do something like:
User.find_by_id(1).followers.first.question_ids.count
in the console to get the count for a single follower.
I feel like I'm almost there.
How do I sort the followers and followed_users through their 'takens' count? (I was also looking at cache_count, which at first seemed promising, but might not be what I need...)
Ruby on Rails does not provide an object oriented mechanism to perform this; you have to write the SQL yourself. In your case, I'd say that the following line SHOULD work:
User.find_by_sql("SELECT users.*, COUNT(questions.id)
AS c FROM users, questions WHERE questions.user_id = users.id
GROUP BY users.id ORDER BY c DESC")
I don't have the actual tables in front of me, so I can't be sure that this is actual valid SQL, but hopefully it should work.
EDIT: There were a few syntax errors with my SQL but they've been fixed. Note that I'm assuming that your tables are called users and questions. They may differ for you.
I have three models:
Class Project < ActiveRecord::Base
has_many :tasks
has_many :tags, :through => :tasks
end
Class Tasks < ActiveRecord::Base
belongs_to :project
has_and_belongs_to_many :tags
end
Class Tags < ActiveRecord::Base
has_and_belongs_to_many :tasks
has_many :projects, :through => :tasks
When I open up console, I can get my Project and Task information as expected:
Tag.find(1).projects
Tag.find(1).tasks
If I want, I can get all the tasks for each project regardless of the tag:
Project.find(1).tasks
For whatever reason, I can't access tasks if I get projects by tag...
something = Tag.find(1).projects
something.tasks
...I get the error:
undefined method `tasks' for #<ActiveRecord::Relation:0x007feae4af0e70>
I've looked for a couple hours and can't find anything that corrects this problem. Based on everything I've found, it should be working... but it's not.
I'm using Rails 3.2.3.
Shouldn't Tag.find(1).tasks give you the same result?
Anyway, the problem you're facing is that you're trying to retrieve an association from a Relation object instead of an instance of your model. Relations can be used to chain query conditions, but you can't directly reference associations from them. So, to get your example working, you'd need to do
p = Tag.find(1).projects.includes(:tasks)
Then reference tasks like this: p[0].tasks.
However I'd just make sure that Tag.find(1).tasks will generate the same SQL and ultimately return the same collection of tasks.
I guess i have a rather simple question since I'm new to Ruby and even newer to ActiveRecords.
What I want to achieve is a class representation with ActiveRecords (and the corresponding SQL schema) that models the following problem:
There exist categories and subcategories (modeled by parent_id)
Products belong to only one category
Each product can have 0..inf features
Features simply have some data fields and are only referenced by the products
My current schema is shown below in the picture:
Is this schema suitable for ActiveRecords? How would the classes look like? I simply cant figure out how the JoinTable fits into the ActiveRecord structure.
Further, how can i model the link from parent_id->categories.id?
Any help appreciated!
cheers
To model the relationships you described you would do:
models/category.rb
class Category < ActiveRecord::Base
has_many :products
has_many :subcategories, :class_name => "Category", :foreign_key => :parent_id
end
models/product.rb
class Product < ActiveRecord::Base
belongs_to :product
has_many :features, :through => :product_features
has_many :product_features
end
models/feature.rb
class Feature < ActiveRecord::Base
has_many :product_features
has_many :products, :through => :product_features
end
models/productfeature.rb
class ProductFeature < ActiveRecord::Base
belongs_to :product
belongs_to :feature
end
Given this structure then you have the join modelled as a Many-to-Many relation. This is useful since the HABTM style of join is going away in Rails 3.1
To get the information, I often use the console rails console for testing and this would allow you do do
#category = Category.first #get the first category
#category.subcategories #returns an array of categories
The traversal of the links is via the relations that you setup in the models, with the intention that its readable, in the context of using sensible names. The self-joins, as per your question, is also covered in Rails Guides: Associations with a good example. The rest of this guide also details the other relationships.
One other thing to remember is to create your migrations so that the join table is created with the id's which are the foreign keys.
My models would look like this:
class Category < ActiveRecord::Base
has_many :products
end
class Product < ActiveRecord::Base
belongs_to :category
has_many :product_features
has_many :features, :through => :product_features
end
class ProductFeature < ActiveRecord::Base
belongs_to :product
belongs_to :feature
end
class Feature < ActiveRecord::Base
has_many :product_features
has_many :products, :through => :product_features
end
Rails has an association called has_and_belongs_to_many. Rails expects a table with two columns to store the join data. I usually use dual has_many to achieve the same results as it gives you flexibility to add additional information in the join table.
Sample code
product.category
product.category = category1
category.products
category.products << product1
product.features
product.features << feature1
feature.products
feature.products << product1
Here is the API for ActiveRecord::Associations::ClassMethods
There are a lot of examples in there of different relationships and how to construct them. It's worth taking the time to understand how/why you construct these associations.
For the Many-to-many join you will want to look at
has_many ..., :through => ...
has_and_belongs_to_many ...
The docs explain when and why to use each.
I have a simple question, but can't seem to find any solution, though I have found things that are similar, but just not exactly what I am looking for.
I have an application where a User has many Assets through the class UserAsset. I want to be able to do current_user.user_assets , but I only want to return records that have an Asset with a specified field value of "active".
This post is similar but I need to use the main model not the join model as a filter.
class UserAsset < ActiveRecord::Base
belongs_to :asset
belongs_to :user
end
class Asset < ActiveRecord::Base
has_many :user_assets
has_many :users, :through => :user_assets
end
class User < ActiveRecord::Base
has_many :user_assets
has_many :assets, :through => :user_assets
end
I tried setting the default scope on Asset, and also some conditions on the has many (user_assets) relationship, but rails is failing to consider the join on the Assets table. ie Unknown column 'asset.live' in 'where clause'. Trying to achieve the following:
#active_user_assets = current_user.user_assets #only where assets.active = true
So how do I use conditions or scopes to achieve this? I need the user_asset object because it contains info about the relationship that is relevant.
Thanks in advance!
You want current_user.assets, then your scopes should work.
Oh, but you want the user_assets. Hmm. I think you need the :include clause to find() but where to put it, I can't be arsed to think of right now.
Perhaps
current_user.user_assets.find(:all, :include => :assets).where('asset.live=?', true)
(I'm not on Rails 3 yet, so that's going to be mangled)
Are you using :through when you really want a HABTM?