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.
Related
So I have a CareerEntry model that has the following attributes: name, job_category, company, group, location, year, full_intern, and it represents the job offers that people have received. full_intern is a string that is either "internship" or "full-time", and represents what the type of the job offer is. All CareerEntries will be created by an Admin interface, so it is essentially acting as a standalone model. This is my question: given a bunch of CareerEntry objects, I want to display a table to display on my careers page (which has an action in a PagesController).
I want the table to be sorted according to multiple attributes. I want each year to be its own section in the table, then within each year, I want the internship entries grouped together and the full-time entries grouped together. Then, within these groupings, I want each job_category to be its own section (job_categories comprise of things like 'Investment Banking,' or 'Technology.')
A very good example of what I'm going for is shown under the "2013" tab in this link.
What is the best way to go about achieving this? I know that in the careers action definition of my PagesController, I could have:
class PagesController < ApplicationController
def careers
#careerentries = CareerEntry.order(:year => :desc, :fullintern => :asc, :job_category => :asc)
end
end
But this would simply return all the entries in the order that I want, and would not allow me to place headers and dividers to separate, say, the job_categories.
Is there any easier way of achieving what I'm looking for?
Perhaps you're looking for .group_by?
Group By
From the link you gave, it looks like you want to group your results by year, like this:
#careerentries = CareerEntry.order(year: :desc, fullintern: :asc, job_category: :asc)
#entries_by_year = #careerentries.group_by { |entry| entry.year }
This gives you all the data, ordered to your specs. You can then sort through it, using the group_by method:
#entries_by_year.each do |entry|
entry.name
end
You could then work this into your table
Good reference Group posts by Year - Rails
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.
On my site I got entries which have category. Site have only 5 categories, so I have dilemma:
Make relationship between category table and entries (category_id) table
OR
Make method which return category name via IF/CASE statement? Like:
case #entry.category.id
when 1
"Games"
when 2
"Movies"
when 3
"Fun"
[...]
end
(I remind that I must get 10 category name per page)
OR
Use array:
cat[1] = "Games"
cat[2] = "Movies"
cat[3] = "Fun"
[...]
<%= cat[#entry.category.id] %>
I think this relation definitely belongs into the database. (adding a category table)
it is the most sane and most scalable option.
It is also the cleanest, because you break the seperation of data, display and logic (MVC: model, view, controller) when hardcoding the categories in your application.
you can easily select the item AND its category with a single query:
SELECT item.*, category.name
FROM item
LEFT JOIN category ON category.id = item.category_id
WHERE some=condition
there are similar queries for INSERTs and UPDATEs (at least in MySQL), so you never need a second query.
If the only thing you care about category is "name", then you should just store the category_name in the entries table.
OR
Make a constant CATEGORY_NAME and wrapper method to get the name with id in the entries table (without using Category table/model at all). eg.,
class Entry
CATEGORY_NAME = [ "Games", "Movies", "Fun"]
def category_name
CATEGORY_NAME[cat_id] #cat_id being just 0,1,2 .. depends how you want to store
end
...
I am sure there are many ways to achieve this anyway.
Hope it helps.
I have a table of questions: title
Each question has answers, in another table: text, question_id
Each answer has votes, in another table: answer_id
I can ask for total votes with
question.votes.count
I have seen how to group the votes db at
http://guides.rubyonrails.org/active_record_querying.html#group
Vote.group("answer_id")
But I want to order my questions by votes. That is ordering an array from a table via the grouping of another table. Is that possible?
q=Question.last
q.answers.order_by_vote #How to do this?
I think my answer could be doing a scope on the answer model that makes the grouping on the subset of votes that belong to the question. Am I right?
Thank you.
First, I think that you mean table when you say DB (database). A table a structure inside a database that holds data for a specific model, for example (questions, votes and answers. In your case you have three tables.
Second, calling attr_accessible :answer_id does not make an attribute searchable by an index. It is searchable by this attribute regardless of whether or not you declare it accessible. It is not an index unless you specify it as an index in the database. attr_accessible means that the attribute can be set using mass-assignment, for example when you call update_attributes.
Finally, if you want to group by answer_id and order by the number of votes, you can do so with the following query:
Vote.select('count(id) as votes, answer_id').group('answer_id').order('votes DESC')
If you want to order by some other value than the one you are grouping by, you'll have to add that to your group as well. This ensures that you aren't getting arbitrary results for the second value. For example:
Vote.group('answer_id').group('column_1').order('column_1 DESC')
I just figured out a way to organize my links by vote count, using the sort method in my links view:
<% #user.links.sort { |a, b| b.votes.sum(:score) <=> a.votes.sum(:score) }.each do |link| %>
votes.sum(:score) grabs the number of votes a particular link has from the votes table.
hope that helps.
I have two models in my rails app with a has many and belongs to association.
Category has many items and Item belongs to category.
These models are associated in the normal way through a category_id column in the Item model.
I'm looking for a quick way of finding all elements in the database with broken associations.
i.e. find all categories that exist with no associated items and items that exist with no associated category.
For example, if I have an item with a category_id of 7, but the category with id 7 has been deleted then this would be considered broken.
For your example, to find items with category_id's for categories which don't exist any more:
Item.where('NOT EXISTS (SELECT * FROM categories where category.id = item.category_id)')
You might want to look at this as well:
A rake task to track down missing database indexes (not foreign keys though, but indexes): https://github.com/eladmeidar/rails_indexes
A very effective way is using find_by_sql to let the database do the heavy lifting:
uncategorized_items = Item.find_by_sql("select * from items where category_id IS NULL")
Another way is a named scope:
class Item < ActiveRecord::Base
scope :uncategorized, where(:category_id => nil) # rails 3
# or...
named_scope :uncategorized, :conditions => 'category_id IS NULL'
end
These are just a couple of ideas. I assume that once you've found these broken associations you plan to fix them, right? You might want to use validates_associated in both models if it's important to you that this not happen again.
You can use find_by_sql and a left outer join to find all the items in one table but not another. Here, I use a downloads table and an image_files table (I've only included the SQL):
SELECT d.*, d.image_file_id
from downloads as d
LEFT OUTER JOIN image_files as i
ON i.id = d.image_file_id
WHERE d.image_file_id IS NULL