I have two models:
Novel has_many :pages
Page belongs_to :novel
I want to list popular Novels according to page count. Essentially, I want Novel models loaded from the outcome of this query:
select p.novel_id, count(*) as count
from pages p
GROUP BY p.novel_id
ORDER BY count DESC
I'm sure there's some cute way to do it in Rails 2.3 using named_scope, but I can't quite get it to work. Plus, if it does work, is it going to be dog slow?
I've considered keeping page_count on Novel, but that seems like a violation of something (convention, normalization, my soul).
Seems like counter cache is the way to go. If you create a column called page_count on the novels table (with an index), Rails will cache the number of pages on the Novel model itself, making this kind of query very easy and performant.
The named_scope on the Novel model then becomes
class Novel < ActiveRecord::Base
named_scope :popular, :order => 'page_count desc'
end
class Page < ActiveRecord::Base
belongs_to :novel, :counter_cache => true
end
For more details check out the counter cache railscast
Yep, that's going to be pretty slow. It's not a horrible thing to cache the page_count in your Novel. Normalization is all well and good, until it impacts performance.
Caching expensive calculations is the essence of most optimizations.
Keeping a counter_cache on the Novel is deemed acceptable in this matter and should aid your query.
In page.rb do:
belongs_to :novel, :counter_cache => true
And in your novels table put a pages_count column. This will be automatically incremented when you create pages and decremented when you remove them.
Related
Hi can anyone tell me how can i increase performance if association returns large no. of records. for example in my app :-
class Restaurant < ActiveRecord::Base
has_many :inventory_items
end
class InventoryItem < ActiveRecord::Base
belongs_to :vendor
end
i am trying to find the vendors of my restuarant as follow :-
current_restaurant.inventory_items.includes(:vendor).uniq
current_restaurant.inventory_items returns large no. of records which takes maximum time. so how can i reduce this time please help me.
There are a number of solutions that you can use depending on how your application is configured and what it needs to do -
Only select the columns that you want, for example, if you are only looking for the IDs, you can use the pluck or select methods.
As Chetan suggested in his answer, you can also add scopes, and in addition to that also add indexes for the columns in the scope depending on what kind of columns they are.
If you are looking at calculated values, consider caching them on the Restaurant table.
You can add a scope to your model and add a condition for the records you wanna fetch. Like
scope :your_scope_name, -> { includes(:vendor).where(*some more conditions*) }
This will help query to not to go through all data
Use pagination, loading all records is never recommended..
see will_paginate OR kaminari gems
Update:
class Restaurant < ActiveRecord::Base
has_many :inventory_items
has_many :vendors, through: :inventory_items
end
Then,
current_restaurant.vendors.uniq
It depends on the size of the tables and how they are indexed, one sub query might be faster than a huge join:
Vendor.where(id: current_restaurant.inventory_items.select(:vendor_id).distinct)
Let's say I have a single web page form user interface with 2 sets of checkboxes. With set 1 checkboxes, I can check off what Trainers I would like ("Jason", "Alexandra, etc.) With set 2 checkboxes, I can check off what animals I would like to see ("Tigers", "Bears", etc.) Once I submit the form with these options, I get back a list of zoos that match the criteria (let's assume all the trainers work at all the zoos and all the animals are at all the zoos for discussion's sake)
We'll be running our database query by "name" (e.g., search using trainer names and animal names, NOT database ids)
Let's say we are using a Postgres database that has hundreds of thousands of rows (if not millions).
Is it more efficient to search using an "ILIKE" query or is it better to do a standard join query (e.g., Zoo.includes(:animals, :trainers).where("animals.name = ? and trainers.name = ?", animal_names, trainer_names)?
Is there a better way than what I just showed in #1 above?
model setup
class Zoo < ActiveRecord::Base
has_many :animals, through: zoo_animals
has_many :trainers, through: zoo_trainers
has_many :zoo_trainers
has_many :zoo_animals
end
class Animal < ActiveRecord::Base
has_many :zoos, through :zoo_animals
has_many :zoo_animals
end
class Trainer < ActiveRecord::Base
has_many :zoos, through :zoo_trainers
has_many :zoo_trainers
end
class ZooAnimal < ActiveRecord::Base
belongs_to :animal
belongs_to :zoo
end
class ZooTrainer < ActiveRecord::Base
belongs_to :zoo
belongs_to :trainer
end
EDIT: let's suppose I don't have access to the database ID's.
LIKE '%Jason%' is much less efficient than querying for the exact string 'Jason' (or querying for an ID), because while exact comparisons and some uses of LIKE can use an index on the column being queried, LIKE with a pattern beginning with a wildcard can't use an index.
However, performance doesn't sound like the most important consideration here. LIKE %Jason% will still probably be fast enough on a reasonably sized database under reasonable load. If the application really needs to search for things by substring (which implies that a search might have multiple results), that requirement can't be met by simple equality.
There are an endless number of higher-powered solutions to searching text, including Postgres built-in full-text search and external solutions like Elasticsearch. Without specific requirements for scaling I'd go with LIKE until it started to slow down and only then invest in something more complicated.
I have models UserVote, Comment, Edit, etc, all of which have a user_id attribute. I'm trying to create a sort of timeline of recent activity, and this has me querying all 5 of my models separately and sorting by datetime. However, with accounts that have a lot of activity, these 5 queries take a very long time to execute. I'd like to find a way to optimize the performance, and I figured combining the 5 queries might work.
I haven't been able to come up with any working query to achieve what I'd like.
Thanks for any help!
I think the best suggestion in the comments is from Steve Jorgensen, with "I have generally seen this done by adding records to an activity log, and then querying that.".
If you want to take this idea to the next level, check out sphinx (a search engine designed for indexing database content). You can integrate easily with rails using thinksphinx - http://freelancing-god.github.com/ts/en/.
Also, as Tim Peters brings up, you really should have indexs on all of your fkeys, regardless of how you solve this - http://apidock.com/rails/ActiveRecord/ConnectionAdapters/SchemaStatements/add_index.
I think it is good idea to use Polymorphic associations for this problem - http://guides.rubyonrails.org/association_basics.html#polymorphic-associations
class TimeLine < ActiveRecord::Base
belongs_to :timelineable, :polymorphic => true
end
class UserVote < ActiveRecord::Base
has_many :time_lines, :as => :timelineable
end
class Comments < ActiveRecord::Base
has_many :time_lines, :as => :timelineable
end
Now you can sort time_line and access associated resources.
I need guidance to understand logic of writing complex queries in rails.
I have three models
Business
has_many :customers
has_many :transactions
Customer
has_many :transactions
belongs_to :business
Transaction
belongs_to :businesss
belongs_to :customer
//transaction model has a attribute amount which tells how much amount has been spent in this particular transaction.
Now I need to implement filter like this. I am posting screenshot cause that will be easy to understand.
Edit
Every Transaction means a visit. Total spent means total amount spent.
I doubt there is a graceful one-query solution that will feet capabilities of AR. But even if there is one, for the sake of performance you'll have to create a material view or aggregate table for total spent ranking values. So assuming you have material view total_spent_ranking(customer_id, rank) you could do the usual AR querying:
(Just a sketch.)
Customer.joins(:transaction, :total_spent_ranking).select('customer.id').group_by('customer.id').having('total_spent_ranking.rank > 15 and count(distinct transaction.id) > 10')
I have three models, basically:
class Vendor
has_many :items
end
class Item
has_many :sale_items
belongs_to :vendor
end
class SaleItem
belongs_to :item
end
Essentially, each sale_item points to a specific item (but has an associated quantity and sale price which might be different from the item's base price, hence the separate model), and each item is made by a specific vendor.
I'd like to sort all sale_items by vendor name, but this means going through the associated item, because that's where the association is.
My first attempt was to change SaleItem to the following:
class SaleItem
belongs_to :item
has_one :vendor, :through => :item
end
Which allows me to look for SaleItem.first.vendor, but doesn't allow me to do something like:
SaleItem.joins(:vendor).all(:order => "vendors.name")
Is there an easy way to figure out these complex associations and sorting? It would be especially great if there were a plugin that could take care of these sort of things. I have a lot of different types of tables to add sorting to in this application, and I feel like this will be a big chunk of the figuring-out work.
This could definitely be done with a more complex SQL query (possibly using find_by_sql), but you could also do it pretty easily in Ruby. Try something like the following:
SaleItem.find(:all, :include => { :items => :vendors }).sort do |first,second|
first.vendor.name <=> second.vendor.name
end
I haven't tested it, so it might not work exactly like this, but it should give you a good idea of one possible solution.
Edit: Found an old blog post that seems to have solved this issue. Hopefully this still works in the lastest version of ActiveRecord.
source: http://matthewman.net/2007/01/04/eager-loading-objects-in-a-rails-has_many-through-association/
Second Edit: Straight from the Rails documentation
To include a deep hierarchy of associations, use a hash:
for post in Post.find(:all, :include => [ :author, { :comments => { :author => :gravatar } } ])
That’ll grab not only all the comments but all their authors and gravatar pictures. You can mix and match symbols, arrays and hashes in any combination to describe the associations you want to load.
There's your explanation.
Do you really need your sale_items sorted by the database, or could you wait until it is presented and do the sorting client side via javascript (there are some great sorting libraries out there) - that would save server CPU and (backend) code complexity.