I'm developing a web application about gift lists in Rails 3. I'd would like to get all the purchases for a certain list. These are the models and their relationships:
class Gift < ActiveRecord::Base
belongs_to :list
has_many :purchases
class List < ActiveRecord::Base
has_many :gifts
class Purchase < ActiveRecord::Base
belongs_to :gift
So, basically, I've tried the following code (I don't think it's the best way to do this at all), and eventhough the results are correct, I've realized that I get a Gift object instead of a Purchase:
#purchases = List.find(params[:id]).gifts.joins(:purchases).select("purchases.*")
Any ideas?
#purchases = List.find(params[:id]).
gifts.joins(:purchases).
map(&:purchases).flatten
or just refactor your models:
class List < ActiveRecord::Base
has_many :gifts
has_many :purchases, :through => :gifts
so
List.find(params[:id]).purchases
If you want all the purchases maybe...
#purchases= List.find(params[:id]).gifts.collect{|g| g.purchases}
Although you may want to split it up and check that List.find returns a valid List.
Related
Let's imagine that I have a CPA tracking system.
I would have following models: an Offer, it has some Landings, each of them has multiple Links, each of the links has a bunch of Visits.
So, I what I want is DRY code, therefore offer_id column within visits table is unacceptable. The workaround here is delegated methods like this:
class Offer < ActiveRecord::Base
has_many :landings
has_many :links, through: :landings
has_many :visits, through: :landings
end
class Landing < ActiveRecord::Base
belongs_to :offer
has_many :links
has_many :visits, through: :links
end
class Link < ActiveRecord::Base
belongs_to :landing
has_many :visits
delegate :offer, to: :landing
end
class Visit < ActiveRecord::Base
belongs_to :link
delegate :landing, to: :link
delegate :offer, to: :link
end
It works nice with a single visit, e.g. visit.offer.id. But what if I need different visits associated with one offer?
The issue is that I'm unable to construct a valid query using ActiveRecord API. It might look like Visits.where(offer: Offer.first), but it doesn't work this way, saying ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: visits.offer: SELECT "visits".* FROM "visits" WHERE "visits"."offer" = 1, which is predictable.
Question: How should I organize my code to make statements like Visits.where(offer: Offer.first) work efficiently without duplicating offer_id column within visits table?
You code was organized nicely, don't need to refactor I think. You can achieve that by defining a scope in Visit like this:
class Visit < ActiveRecord::Base
scope :from_offer, -> (offer) {
joins(link: :landing).where(ladings: {offer_id: offer.id})
}
scope :from_landing, -> (landing) {
joins(:link).where(links: {landing_id: landing.id})
}
end
So the query will be:
Visit.from_offer(Offer.first)
I'm having some trouble trying to fetch some models via SQL in rails and I was wondering if anyone knows of a good solution for this particular problem. Basically, these are what my classes look like:
class SubscriberList < ActiveRecord::Base
has_many :subscriptions
end
class Subscription < ActiveRecord::Base
has_many :messages
belongs_to :subscription_list
end
class Announcement < ActiveRecord::Base
has_many :messages
end
class Message < ActiveRecord::Base
belongs_to :subscription
belongs_to :announcement
end
Now, I want to access all the Announcements for a SubscriptionList excluding duplicates. Is this possible? Can it be done with a single SQL query or is that just wishful thinking?
For example here's what I want:
class SubscriptionList < ActiveRecord::Base
def announcements
Announcements.joins(:messages).where(message: { subscription: {subscription_list: self} })
end
end
I think your idea is correct in general. Try this variant
Announcements.
joins(messages: {subscription: :subscription_list}).
where(subscription_lists: {id: self.id})
# opposite
SubscriptionList.
joins(subscriptions: {messages: :announcement}).
where(announcements: {id: self.id})
Notes:
* these queries may return duplicates - so uniq can be added to them
* self can be omitted (I wrote it to show that this is id of instance and avoid missunderstanding)
I have the following table structure
manufacturers --> products ---> available_sizes_products <-- sizes
and the following models
class Manufacturer < ActiveRecord::Base
has_many :products
end
class Product < ActiveRecord::Base
has_many :sizes, :through => :available_sizes_products
has_many :available_sizes_products
end
class AvailableProductSize < ActiveRecord::Base
belongs_to :sizes
belongs_to :products
end
class Size < ActiveRecord::Base
has_many :products, :through => :available_sizes_products
has_many :available_sizes_products
end
I need to get a unique list of manufacturers, that have products in size "XL" or "L" for example.I'm getting lost in the chaining of joins etc.
class Manufacturer < ActiveRecord::Base
def self.with_sizes(sizes=[])
#sizes = Sizes.find(sizes)
...
end
end
Can someone help me with that ? Trying to do the Rails 4 way rather than drop down to SQL, since I need the query to run on several DBS
Thanks
First of all you have to use single form of noun in belongs_to expression.
And for the query try this one:
Manufacturer.includes(:products).where(products: (size: "XL"))
I use "includes" to avoid N+1 query. Otherwise it will send two queries: one for Manufacturers and one for products. Write back, if this one doesn't fit your need.
EDIT
BTW, if you want to use exactly joining, write joins instead of includes.
Everything is here:
http://guides.rubyonrails.org/active_record_querying.html#joining-tables
and here:
http://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations
After going through the docs for joins
this is what worked :
Manufacturer.joins(products: :sizes).where(sizes: {id:ids}).distinct
This Rails way returns the model correctly.
I have a problem with fetching data from DB, where is between models association kind through.
On my site, I have a categories, like a sports, news, weather etc. When an user is logged in and has a selected the categories, from which want to see the articles, then I would like to display only these articles.
Here's how looks like my models:
class User < ActiveRecord::Base
has_many :user_categories
has_many :categories, :through => :user_categories
end
class Category < ActiveRecord::Base
has_many :articles
has_many :user_categories
has_many :users, :through => :user_categories
end
class UserCategory < ActiveRecord::Base
belongs_to :user
belongs_to :category
end
class Article < ActiveRecord::Base
belongs_to :category
end
But I still can't find the way, how to get all articles from user's selected categories... I tried something like
Article.joins("LEFT JOIN categories ON category.id = user_categories.category_id").where('user_categories.user_id = ?', current_user.id)
I would grateful for every advice!
Thank you
Here's one way to do it:
Article.where(:category_id => current_user.categories.map {|c| c.id})
That will create 2 queries. First one will return a list of the current user's categories. Then the ruby map function will create an array containing the ids of those categories. The second query will then return a list of articles whose category_id is in the array of ids. The second query will look something like:
select articles.* from articles where articles.category_id in(1,2,3);
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.