I have two tables:
manufacturers and products
Both tables have a column "signature" which is unique.
manufacturer model:
class Manufacturer < ApplicationRecord
has_many :products, foreign_key: 'signature', primary_key: 'signature'
end
product model:
class Product < ApplicationRecord
belongs_to :manufacturer, foreign_key: 'signature', primary_key: 'signature'
end
In my products index view I'd like to display the value of column 'active' from table manufacturer.
# products/index.html.erb
<% #products.each do |product| %>
<%= product.manufacturer.active %>
<% end %>
I'm getting the error
undefined method `active' for nil:NilClass
How can I access the active attribute of manufacturer model from products index view? I suppose
product.manufacturer.active
isn't the right way.
In your code example you have to make sure that every product has an manufacturer. Else .active would fail on a manufacturer = nil.
As a fail save if there are products without manufacturer you can use the Safe Navigation Operator &. as mentioned here Available from ruby2.3
product.manufacturer&.active
As an alternative you could make the .active call conditionally like
product.manufacturer.active unless manufactuer.nil?
or
product.manufacturer.active if manufactuer
Related
The models I have:
Category:
class Category < ApplicationRecord
has_many :categorizations
has_many :providers, through: :categorizations
accepts_nested_attributes_for :categorizations
end
Provider:
class Provider < ApplicationRecord
has_many :categorizations
has_many :categories, through: :categorizations
accepts_nested_attributes_for :categorizations
end
Categorization:
class Categorization < ApplicationRecord
belongs_to :category
belongs_to :provider
has_many :games, dependent: :destroy
accepts_nested_attributes_for :games
end
Game:
class Game < ApplicationRecord
belongs_to :categorization
end
I need to display the games, that belongs to a specific provider. I tried to do it like:
<% #provider.categorizations.joins(:games).each do |game| %>
<%= game.title %>
<% end %>
It gives me an error: NoMethodError: undefined method 'title' for #<Categorization:0x007f2cf6ee49e8>. So, it loops through the Categorization. What is the best way to loop through the joined games table? Thanks.
First, you should do the request in your controller, or even better call a scope (defined in a model) from the controller.
Do not forget that Active Record is just an ORM, a tool allowing you to manipulate SQL.
With #provider.categorizations.joins(:games) you are not asking for games. You are asking for the categorizations and you do a JOIN with the games table. This joins is usually to allow to filter by games attributes.
To do what you want you should do the following :
#games = Game.joins(:categorization).where('categorization.provider_id = ?',#provider.id)
As you can see, the join do not return categorization, it allow me to use categorization as a filter.
You should always be aware of the SQL generated by Active Record. Look at the SQL query generated in your server's traces.
I'm guessing 'title' is an attribute of games and not categorization, so you either need to return an array of games, or add a select on the end to pull the title attribute into the categorization object, like so:
<% #provider.categorizations.joins(:games).select('dba.games.title').each do |game| %>
<%= game.title %>
<% end %>
Just to add- you shouldn't really be doing this in the view file. I'd go as far as not even doing this in the controller. I tend to encapsulate this sort of logic into a service class, which is instantiated in the controller to return a set of results. The controller should only be passing the result set on, which is then presented by the view.
class Provider < ActiveRecrord::Base
# this could be a scope instead, or in a seperate class which
# the provider model delegates to- whatever floats you boat
def get_games
# you could use pluck instead, which would return an array of titles
categorizations.joins(:games).select('dba.games.title')
end
end
class ProviderController < ApplicationController
def show
provider = Provide.find(params[:id])
#games = provider.get_games
end
end
<% #games.each do |game| %>
<%= game.title %>
<% end %>
I am looking for a way to show a count of how many images there are for a category but obtained through a has_many association. I have been reading a little on counter_cache but as yet no joy on an implementation
class Category < ActiveRecord::Base
has_many :image_categories
has_many :images, through: :image_categories
end
class ImageCategory < ActiveRecord::Base
# Holds image_id and category_id to allow multiple categories to be saved per image, as opposed to storing an array of objects in one DB column
belongs_to :image
belongs_to :category
end
class Image < ActiveRecord::Base
# Categories
has_many :image_categories, dependent: :destroy
has_many :categories, through: :image_categories
end
Controller
#categories = Category.all
View
<% #categories.each do |c| %>
<li>
<%= link_to '#', data: { :filter => '.' + c.name.delete(' ') } do %>
<%= c.name %> (<%= #count here %>)
<% end %>
</li>
<% end %>
A couple important things to consider with counter_cache:
Certain Rails methods can update the database while bypassing callbacks (for instance update_column, update_all, increment, decrement, delete_all, etc.) and can cause inconsistent values for a counter cache. Same applies to any database changes outside of Rails.
Creating/deleting a child model always requires updating the parent. To ensure consistency of the counter cache Rails uses an additional DB transaction during this update. This usually isn't a problem but can cause database deadlocks if your child model is created/deleted frequently, or if the parent model is updated frequently. (http://building.wanelo.com/2014/06/20/counter-cache-a-story-of-counting.html)
These problems will be exacerbated since you're using a counter cache across a join table.
If you want to do an efficient dynamic count, that's always up to date, then you can use a custom select with a grouped join:
#categories = Category.select("categories.*, COUNT(DISTINCT images.id) AS images_count").joins(:images).group("categories.id")
<% #categories.find_each do |c| %>
<li>
<%= link_to '#', data: { :filter => '.' + c.name.delete(' ') } do %>
<%= c.name %> (<%= c.images_count # <- dynamic count column %>)
<% end %>
</li>
<% end %>
The cost of this grouped join should be very small provided your foreign keys are indexed, and I'd strongly consider taking this approach if you need images_count to always be consistent with the true value, or if images are frequently being created or destroyed. This approach may also be easier to maintain in the long run.
Since you are looking for an efficient way, i would suggest using counter_cache
Here is how your models should look like:
class Category < ActiveRecord::Base
has_many :image_categories
has_many :images, through: :image_categories
end
class ImageCategory < ActiveRecord::Base
# Holds image_id and category_id to allow multiple categories to be saved per image, as opposed to storing an array of objects in one DB column
belongs_to :image, counter_cache: :category_count
belongs_to :category, counter_cache: :image_count
end
class Image < ActiveRecord::Base
# Categories
has_many :image_categories, dependent: :destroy
has_many :categories, through: :image_categories
end
You'll need to add image_count field to your categories table and category_count in images table.
Once you are done adding the counters and fields, you'd need to reset the counters so that the fields are updated with the correct count values for the records already present in your db.
Category.find_each { |category| Category.reset_counters(category.id, :images) }
Image.find_each { |image| Image.reset_counters(image.id, :categories) }
i have 2 models one is listing and user
user has_many listings
listing belongs_to user
i have a view setup , i want to display for each user their own listings count ,i try this code :
<% User.all.each do |user| %>
<%= user.listings.count %>
<% end %>
i want to grab the listing count for each user . i found a bunch of solution here , all return the loop .other solutions i tried is to create a class method .
def count_listings
Listing.where(:user_id => user.id).count
end
try to call this way <%= User.count_listings%> it doesn't work .
for some reason there something i'm missing ,can't quite figure it out .
The :counter_cache option can be used to make finding the number of belonging objects more efficient. Consider these models:
class Order < ActiveRecord::Base
belongs_to :customer
end
class Customer < ActiveRecord::Base
has_many :orders
end
With these declarations, asking for the value of #customer.orders.size requires making a call to the database to perform a COUNT(*) query. To avoid this call, you can add a counter cache to the belonging model:
class Order < ActiveRecord::Base
belongs_to :customer, counter_cache: true
end
class Customer < ActiveRecord::Base
has_many :orders
end
With this declaration, Rails will keep the cache value up to date, and then return that value in response to the size method.
Although the :counter_cache option is specified on the model that includes the belongs_to declaration, the actual column must be added to the associated model. In the case above, you would need to add a column named orders_count to the Customer model. You can override the default column name if you need to:
class Order < ActiveRecord::Base
belongs_to :customer, counter_cache: :count_of_orders
end
class Customer < ActiveRecord::Base
has_many :orders
end
Counter cache columns are added to the containing model's list of read-only attributes through attr_readonly.
source: Rails guide on associations
..scroll down to options of belongs_to
If all you need is what you show in the example you can do it better as follows
<% Listing.group(:user_id).count.each do |user, count| %>
<%= "user: #{user} has #{count} listings" %>
<% end %>
This does a single query to the database and fetches only what you need.
SELECT COUNT(*) AS count_all, user_id AS user_id FROM `listings` GROUP BY user_id
and returns a hash like:
{
1: 123,
2: 231
}
#{ user_id: count }
Fairly new to Rails, building an e-commerce system.
I have a tree-like structure of products -> skus -> line_items
where:
class LineItem < ActiveRecord::Base
belongs_to :sku
belongs_to :cart
class Sku < ActiveRecord::Base
belongs_to :product
class Product < ActiveRecord::Base
has_many :skus
has_many :line_items, :through => :skus
The Product model has a boolean field that determines whether or not a specific product requires a license.
Multiple line_items are added to a cart, so that:
#cart.line_items
returns an array of line items.
At the order stage, I need to determine whether or not any of the line items need a license, and if so, display the license for acceptance.
I have tried linking scopes:
class LineItem < ActiveRecord::Base
scope :license?, joins(:sku) & Sku.license?
class Sku < ActiveRecord::Base
scope :license?, joins(:product) & Product.license?
class Product < ActiveRecord::Base
scope :license?, where(:license => true)
#cart.line_items.license?
results in an empty array, even when #cart.line_items contains items that have product.license as true.
I've tried:
#cart.line_items.joins(:sku).joins(:product).where(:license => true)
which returns an ActiveRecord::Relation, but
#cart.line_items.joins(:sku).joins(:product).where(:rct => true).empty?
#cart.line_items.joins(:sku).joins(:product).where(:rct => true).to_a
#cart.line_items.joins(:sku).joins(:product).where(:rct => true).all
all fail to give either a boolean (in the first case) or an array in the second two cases.
I can loop through:
<% #cart.line_items.each do |item| %>
<h4><%= item %></h4>
<h4><%= item.sku.product.license %></h4>
<% end %>
and see all the correct booleans, but there has to be a better way to do this than either using a variation of this loop in my order view, or having to create a class method to loop through and generate the boolean.
Any ideas?
It seems like the Product is the one that understands whether it needs a licence or not. In which case, you need to go up the chain from the line_item all the way to the product to fetch that info. You could add a needs_license? method on the LineItem class which delegates to its Sku, which delegates to its product, and then filter out LineItems like so:
class LineItem
def needs_license?
sku.needs_license?
end
end
class Sku
def needs_license?
product.needs_license?
end
end
class Product
def needs_license?
license
end
end
Finally,
#cart.line_items.select(&:needs_license?)
i have the following Problem, i Have the following in my customer bill view
<%= f.collection_select :product_id,Product.all,:id,:name %>
This is getting list of all the products from "Product" model and giving option to select from it. But i want to select the list of products from the "StoreOpeningStock" model.
I have these in my model
class Product< ActiveRecord::Base
has_many :store_opening_stocks
has_many :customer_bills
attr_accessible :name
end
class StoreOpeningStock < ActiveRecord::Base
attr_accessible :product_id
belongs_to :product
end
class CustomerBill < ActiveRecord::Base
attr_accessible :product_id
belongs_to :product
accepts_nested_attributes_for :store_opening_stock
end
Can anyone guide me how i can get product name and id from store_opening_stock??? Should i use Helpers??? or is there any other way?? Thanks in advance
I tried using helpers
def getting_prod_names
#sto = StoreOpeningStock.all
for x in #sto
[
['{x.product.title}', '{x.product_id}']
]
end
end
getting following output
<%= f.select :product_id, options_for_select(getting_prod_names) %>
ANy Help?? :)
When you create a form the data used to ccreate a collection_select isnt limited to the Class your going to create an object for. You could simply do the following:
<%= f.collection_select :product_id,StoreOpeningStock.all,:product_id ,:name %>
This should to it for you,...
add this to your StoreOpeningStock class:
def name
return self.product.name unless self.product.nil?
""
end
You need to clarify the relationship between your models...
But just to give you an idea. You can define the collection of products you want to display in your controller, inside the action related to the view (where you are displaying the collection).
Controller:
#products= #here you should call all products you want
Then, your collection of products can be displayed like:
<%= f.collection_select :product_id, #products,:id,:name %>
EDIT
You need to revise the relationship between your models. A product has many customer_bills, but are you sure that each customer_bill belongs to a single product?
I think you have a many-to-many relationship, as a customer_bill can also have many products.
If I understand it right, the solution is to create a ProductLine model between this many-to-many relationship.
Also, what is the difference between Product and StoreOpeningStock? What attributes have you included in the StoreOpeningStock?
If you have created this model only to show the availability of products, why don't you add an attribute in the Product model, for example a boolean column called availability.
So you want to find all products that have a StoreOpeningStock.
This is solely a model concern and have nothing to do with helpers.
class Product
# Find all products that have a StoreOpeningStock
def self.in_stock
find(StoreOpeningStock.product_ids)
end
end
class StoreOpeningStock
# Collect all product ids from stocks
def self.product_ids
uniq.pluck(:product_id)
end
end
Now you can use Product.in_stock instead of Product.all to have the only ones in stock.
I'd add a scope to your products model:
class Product< ActiveRecord::Base
has_many :store_opening_stocks
has_many :customer_bills
attr_accessible :name
scope :having_store_opening_stocks, :joins => : store_opening_stocks, :select => 'distinct product.*', :conditions => 'store_opening_stocks.product > 0'
end
Then you can use Product.all.having_store_opening_stocks to select only products with such stocks, for example:
<%= f.select :product_id, Product.having_store_opening_stocks.map { |product| [product.name, product.id] } %>