This is a simple ruby question I believe. In my app, I have Product model that has_many Reviews. Each Review has an attribute of an "overall" rating which is an integer.
What I want to do is display the top ten Products based on the average of their overall ratings. I've already gotten this to work, BUT, I also want to sort Products that have the SAME overall rating by a secondary aggregate attribute, which would be how MANY reviews that Product has. Right now, if I have 3 products with the same average overall rating, they seem to be displayed in random order.
So far my code is:
Controller
#best = Product.has_reviews.get_best_products(10)
Product Model
scope :has_reviews, joins{reviews.outer}.where{reviews.id != nil}
def self.get_best_products(number)
sorted = self.uniq
sorted = sorted.sort { |x, y| y.reviews.average("overall").to_f <=> x.reviews.average("overall").to_f }
sorted.first(number)
end
I've tried this for my model code:
def self.get_best_products(number)
sorted = self.uniq.sort! { |x, y| x.reviews.count.to_f <=> y.reviews.count.to_f }
sorted = sorted.sort { |x, y| y.reviews.average("overall").to_f <=> x.reviews.average("overall").to_f }
sorted.first(number)
end
...but it does not do what I want it to do. I am just iterating through the #best array using each in my view.
---UPDATE
OK now I am trying this:
Controller:
#best = Product.get_best_products(6)
Model:
def self.get_best_products(number)
self.joins{reviews}.order{'AVG(reviews.overall), COUNT(reviews)'}.limit(number)
end
But I am getting this error:
PGError: ERROR: column "products.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT "products".* FROM "products" INNER JOIN "reviews" ...
I am using the Squeel gem btw to avoid having direct SQL code in the model.
----UPDATE 2
Now I added the 'group' part to my method but I am still getting an error:
def self.get_best_products(number)
self.joins{reviews}.group('product.id').order{'AVG(reviews.overall), COUNT(reviews)'}.limit(number)
end
I get this error:
PGError: ERROR: missing FROM-clause entry for table "product"
LINE 1: ...eviews"."product_id" = "products"."id" GROUP BY product.i...
product.rb
scope :best_products, (lambda do |number|
joins(:reviews).order('AVG(reviews.overall), COUNT(reviews)').limit(number)
)
products_controller.rb
Product.best_products(10)
This makes sure everything happens in the database, so you won't get records you don't need.
If I got it right here is my idea of how I would do it:
As products has many reviews and reviews has an overall attribute I would add a reviews_counter column to the products table that will increment with each added review, this way you'll be able to gain a little more db performance as you don't have to count all the products reviews to get the most reviewed one.
Now you'll get the products ordered by reviews_counter:
#best_products = Products.order("reviews_counter desc")
and next you'll get the reviews for each product ordered by overall:
<% for prod in #best_products %>
<%= prod.reviews.order("overall desc") %> # can do all this or more in helper
<% end %>
also ordering this way, if you have 3 reviews with the same overall you can one more order() statement and sort it by name or id or whatever you like so they don't display in random order.
This is just my idea of how I would do it, I worked recently on an app that required something similar and we just added a counter_field to our model, it's not illegal to do so :)
p.s. it's not very clear for me how many records you would want to display for each so you'll just need to add .limit(5) for exemple to get only the first 5 reviews of a product.
Related
I am building a feature in my app to create purchase orders. I have classic tables purchase_orders and purchase_order_lists.
purchase_order has many purchase_order_lists and purchase_order_lists belongs_to purchase_order. Foreign key is on purchase_orders table, column PURCHASE_ORDER. Database table names are capital.
In my purchase_orders controller I have:
def show
#purchase_order = PurchaseOrder.find(params[:ID])
#purchase_order_list = PurchaseOrderList.find(params[:ID])
end
In my model purchase_oder_list.rb
def total
(self.UNITS * self.PRICEBUY)
end
In my view purchase_orders/show
<td><%= purchase_order_list.total %></td>
which return the correct value for each purchase order list row.
Then in the same view to show the total:
#purchase_order_list.to_a.sum(&:total)
which should show the total of method total but it raises the error
Couldn't find PurchaseOrderList with 'ID'=POID-00001
as it is looking for a Purchase Order ID among Purchase Order List IDs.
How can I fix it to return the sum of method totalfor a certain purchase order?
The problem was that I was using find while there are many purchase_order_lists for one purchase order.
To fix I used where instead:
#purchase_order_list = PurchaseOrderList.where(PURCHASE_ORDER: params[:ID])
I wasn't sure how to ask this question. I am new to Ruby on Rails and am still figuring out how to piece everything together.
I have books, orders, products and users. Within a specific view, I would like to display one product_id per user — most users will have the same product_id multiple times.
Here's my book view.
<% #orders.each do |order| %>
<% order.product.books.each do |book| %>
<%= link_to book.title %>
<% end %>
<% end %>
In my book controller I have
def index
#orders = Order.select(:product_id).distinct
#books = Book.page params[:page]
end
All of this works well (view shows one product_id per order product_id, even if there are duplicates) until I call order.created_at which gives a missing attribute error. I know this error is because I am only requesting :product_id on order, but when I add :created_at (#orders = Order.select(:product_id, :created_at).distinct) to the select query I get duplicate :product_ids.
What am I missing?
Well, you have to think about what that would look like. When you are selecting rows by a distinct product_id you are discarding all other order rows that have the same product_id. But when you add created_at back into the mix your resulting record set will include the same product_id because the distinct is operating against the tuple of (product_id, created_at) instead of just the product_id.
Your original #orders isn't actually all of your orders, it's just a subset because it chose a unique one per product_id.
I find it helpful to append to_sql to the end of a query to see what the actual SQL coming out of ActiveRecord is doing:
> Order.select(:product_id).distinct.to_sql
=> SELECT DISTINCT "orders"."product_id" FROM "orders"
> Order.select(:product_id, :created_at).distinct.to_sql
=> SELECT DISTINCT "orders"."product_id", "orders"."created_at" FROM "orders"
Try running those in the database and you'll see what data ActiveRecord is using to construct ActiveRecord instances and realize that ActiveRecord is just taking whatever rows come back in the data and manufacturing objects based on that.
I'm trying to rank my user's in order of an integer. The integer I'm getting is in my User Model.
def rating_number
Impression.where("impressionable_id = ?", self).count
end
This gives each User on the site a number (in integer form). Now, on the homepage, I want to show an ordered list that places these user's in order with the user with the highest number first and lowest number second. How can I accomplish this in the controller???
#users = User....???
Any help would be appreciated!
UPDATE
Using this in the controller
#users = User.all.map(&:rating_number)
and this for the view
<% #users.each do |user| %>
<li><%= user %></li>
<% end %>
shows the user's count. Unfortunately, the variable user is acting as the integer not the user, so attaching user.name doesn't work. Also, the list isn't in order based on the integer..
The advice here is still all kinds of wrong; all other answers will perform terribly. Trying to do this via a nested select count(*) is almost as bad an idea as using User.all and sorting in memory.
The correct way to do this if you want it to work on a reasonably large data set is to use counter caches and stop trying to order by the count of a related record.
Add a rating_number column to the users table, and make sure it has an index defined on it
Add a counter cache to your belongs_to:
class Impression < ActiveRecord::Base
belongs_to :user, counter_cache: :rating_number
end
Now creating/deleting impressions will modify the associated user's rating_number.
Order your results by rating_number, dead simple:
User.order(:rating_number)
The advice here is just all kinds of wrong. First of model your associations correctly. Secondly you dont ever want to do User.all and then sort it in-memory based on anything. How do you think it will perform with lots of records?
What you want to do is query your user rows and sort them based on a subquery that counts impressions for that user.
User.order("(SELECT COUNT(impressions.id) FROM impressions WHERE impressionable_id = users.id) DESC")
While this is not terribly efficient, it is still much more efficient than operating with data sets in memory. The next step is to cache the impressions count on the user itself (a la counter cache), and then use that for sorting.
It just pains me that doing User.all is the first suggestion...
If impressions is a column in your users table, you can do
User.order('impressions desc')
Edit
Since it's not a column in your users table, you can do this:
User.all.each(&:rating_number).sort {|x,y| y <=> x }
Edit
Sorry, you want this:
User.all.sort { |x, y| y.rating_number <=> x.rating_number }
I am trying to achieve by reducing the numbers of queries using ActiveRecord 3.0.9. I generated about 'dummy' 200K customers and 500K orders.
Here's Models:
class Customer < ActiveRecord::Base
has_many :orders
end
class Orders < ActiveRecord::Base
belongs_to :customer
has_many :products
end
class Product < ActiveRecord::Base
belongs_to :order
end
when you are using this code in the controller:
#customers = Customer.where(:active => true).paginate(page => params[:page], :per_page => 100)
# SELECT * FROM customers ...
and use this in the view (I removed HAML codes for easier to read):
#order = #customers.each do |customer|
customer.orders.each do |order| # SELECT * FROM orders ...
%td= order.products.count # SELECT COUNT(*) FROM products ...
%td= order.products.sum(:amount) # SELECT SUM(*) FROM products ...
end
end
However, the page is rendered the table with 100 rows per page. The problem is that it kinda slow to load because its firing about 3-5 queries per customer's orders. thats about 300 queries to load the page.
There's alternative way to reduce the number of queries and load the page faster?
Notes:
1) I have attempted to use the includes(:orders), but it included more than 200,000 order_ids. that's issue.
2) they are already indexed.
If you're only using COUNT and SUM(amount) then what you really need is to retrieve only that information and not the orders themselves. This is easily done with SQL:
SELECT customer_id, order_id, COUNT(id) AS order_count, SUM(amount) AS order_total FROM orders LEFT JOIN products ON orders.id=products.order_id GROUP BY orders.customer_id, products.order_id
You can wrap this in a method that returns a nice, orderly hash by re-mapping the SQL results into a structure that fits your requirements:
class Order < ActiveRecord::Base
def self.totals
query = "..." # Query from above
result = { }
self.connection.select_rows(query).each do |row|
# Build out an array for each unique customer_id in the results
customer_set = result[row[0].to_i] ||= [ ]
# Add a hash representing each order to this customer order set
customer_set << { :order_id => row[1].to_i, :count => row[2].to_i, :total => row[3].to_i } ]
end
result
end
end
This means you can fetch all order counts and totals in a single pass. If you have an index on customer_id, which is imperative in this case, then the query will usually be really fast even for large numbers of rows.
You can save the results of this method into a variable such as #order_totals and reference it when rendering your table:
- #order = #customers.each do |customer|
- #order_totals[customer.id].each do |order|
%td= order[:count]
%td= order[:total]
You can try something like this (yes, it looks ugly, but you want performance):
orders = Order.find_by_sql([<<-EOD, customer.id])
SELECT os.id, os.name, COUNT(ps.amount) AS count, SUM(ps.amount) AS amount
FROM orders os
JOIN products ps ON ps.order_id = os.id
WHERE os.customer_id = ? GROUP BY os.id, os.name
EOD
%td= orders.name
%td= orders.count
%td= orders.amount
Added: Probably it is better to create count and amount cache in Orders, but you will have to maintain it (count can be counter-cache, but I doubt there is a ready recipe for amount).
You can join the tables in with Arel (I prefer to avoid writing raw sql when possible). I believe that for your example you would do something like:
Customer.joins(:orders -> products).select("id, name, count(products.id) as count, sum(product.amount) as total_amount")
The first method--
Customer.joins(:orders -> products)
--pulls in the nested association in one statement. Then the second part--
.select("id, name, count(products.id) as count, sum(product.amount) as total_amount")
--specifies exactly what columns you want back.
Chain those and I believe you'll get a list of Customer instances only populated with what you've specified in the select method. You have to be careful though because you now have in hand read only objects that are possibly in in invalid state.
As with all the Arel methods what you get from those methods is an ActiveRecord::Relation instance. It's only when you start to access that data that it goes out and executes the SQL.
I have some basic nervousness that my syntax is incorrect but I'm confident that this can be done w/o relying on executing raw SQL.
Ok, I'm not sure that my title was clear enough, but I will try to explain
I have two tables: orders that has_many items and items that belongs_to orders.
I just started to learn RoR and stuck with a simple task. All I want is to
display orders and related items like this:
Order 1:
Item 1
Item 2
Order 2:
Item 1
Item 2
...
I know how to display orders or items separately, I know how to display items' orders (item.order.id), but how to display orders and items in the table like above? In template where I display orders I could go through each item every iteration and compare it foreign order_id with order.id, but that would be awkward. I'm supposing that I should get items into some kind of multidimensional hash where key would be order_id and then I could just refer to this hash by order id and get all items in it, but I'm not sure it's correct.
I hope what I have written here is understandable.
When you define a has_many relation, you automatically get the methods to query those objects. In this case, the method order.items.
So you can do:
Order.find_each do |order|
puts "Order #{order.id}:"
order.items.each do |item|
puts "Item #{item.id}"
end
end
(I used find_each method, which is available from Rails 2.3+. You could use a simple Order.all.each though.