Not sure this could fall in performance section as well as model/database section, so here goes....
Let's say I have 3 models:
Movie {
has_one :interest, :as => :resource
}
Song {
has_one :interest, :as => :resource
}
Story {
has_one :interest, :as => :resource
}
and ...
Interest {
belongs_to :resource, :polymorphic => true
}
Now, if I need a list of all interests for all movies, and I want to show also the date those Movies objects were created (to say how old they were), then I use the lookup on resource_type attribute and then #some_interest.resource.created_at.
The problem with this is if I have 100 movie interests, then I will get 101 queries right ? So linear degradation. I tried using :include => [:resource] in my query call, but it says cannot use include in polymorphic associations.
How can I either eager load or optimize this problem to avoid this severe degradation ??
Any help would be greatly appreciated !!
If you are using searchlogic, there is a special syntax to deal with polymorphic relationships that may help. You can search on the has side of the relationship by specifying the name of the related class suffixed with type.
E.g. given your models, you ought to be able to do something like this to get movies created in the last 90 days:
Interest.resource_movie_type_created_at_gt(Time.now-90.days)
Searchlogic sets up the join on the related model for you, which should allay performance concerns.
Of course you can always write your own SQL using the find_by_sql method.
PS. one very helpful trick is to turn on logging in the Rails console while writing searches. This allows you to see the SQL generated right in the console without having to dig through the logs.
Related
I have the following models:
Car:
has_many :car_classes
CarClass:
belongs_to :Car
belongs_to :CarMainClass
CarMainClass:
has_many :car_classes
What I want to do is to count the amount of cars in CarClass grouped by the car_main_class_id but then linked to the main_class_symbol which is in CarMainClass.
The query I have now is:
CarClass.group(:car_main_class_id).count(:car_id) => {43=>79, 45=>4 ...}
Which is almost what I want, except that I end up only with the :car_main_class_id which I to be the :main_class_symbol from CarMainClass:
{"A1"=>79, "A2"=>4 ...}
I tried joining the tables and custom select options, but they didn't work.
Can this be done in a query in which I don't have to iterate through the main classes again?
Many thanks for your help!
Instead of having a SQL approach and using a "count/group by", you should look to a very simple feature of Rails ActiveRecords : the counter_cache column.
For example, you can add a column "car_classes_count" in the CarMainClass, and in CarClass class, you do like this :
CarClass:
belongs_to :car
belongs_to :car_main_class, :counter_cache => true
You can do the same with a column "car_class_count" in Car.
I don't know if it can help, but I had the same kind of problems when I started to develop with Rails. I tried to do some unsuccessful crazy SQL queries (queries that worked w/ sqlite, but did not w/ postgres) and I finally choose an other approach.
Try this:
CarClass.includes(:car_main_class => :car_classes)
.group(:car_main_class_id).map { |cc|
{ cc.car_main_class.main_class_symbol => cc.car_main_class.cars.size }
}
Although this is quite ugly - I agree with #Tom that you should try to think of more meaningful class names.
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 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.
I have a polymorphic association like this -
class Image < ActiveRecord::Base
has_one :approval, :as => :approvable
end
class Page < ActiveRecord::Base
has_one :approval, :as => :approvable
end
class Site < ActiveRecord::Base
has_one :approval, :as => :approvable
end
class Approval < ActiveRecord::Base
belongs_to :approvable, :polymorphic => true
end
I need to find approvals where approval.apporvable.deleted = false
I have tried something like this -
#approvals = Approval.find(:all,
:include => [:approvable],
:conditions => [":approvable.deleted = ?", false ])
This gives "Can not eagerly load the polymorphic association :approvable" error
How can the condition be given correctly so that I get a result set with approvals who's approvable item is not deleted ?
Thanks for any help in advance
This is not possible, since all "approvables" reside in different tables. Instead you will have to fetch all approvals, and then use the normal array methods.
#approvals = Approval.all.select { |approval| !approval.approvable.deleted? }
What your asking, in terms of SQL, is projecting data from different tables for different rows in the resultset. It is not possible to my knowledge.
So you'll have to be content with:
#approvals = Approval.all.reject{|a| a.approvable.deleted? }
# I assume you have a deleted? method in all the approvables
I would recommend either of the answers already presented here (they are the same thing) but I would also recommend putting that deleted flag into the Approval model if you really care to do it all in a single query.
With a polymorphic relationship rails can use eager fetching on the polys, but you can't join to them because yet again, the relationships are not known so the query is actually multiple queried intersected.
So in the end if you REALLY need to, drop into sql and intersect all the possible joins you can do to all the types of approvables in a single query, but you will have to do lots of joining manually. (manually meaning not using rails' built-in mechanisms...)
thanks for your answers
I was pretty sure that this couldn't be done. I wanted some more confirmation
besides that I was hoping for some other soln than looping thru the result set
to avoid performance related issues later
Although for the time being both reject/select are fine but in the long run I
will have to do those sql joins manually.
Thanks again for your help!!
M
The business logic is this: Users are in a Boat through a join table, I guess let's call that model a Ticket. But when a User instance wants to check who else is on the boat, there's a condition that asks if that user has permission see everyone on the Boat, or just certain people on the Boat. If a User can see everyone, the normal deal is fine: some_user.boats.first.users returns all users with a ticket for that boat. But for some users, the only people that are on the boat (as far as they're concerned) are people in, let's say the dining room. So if User's ticket is "tagged" (using an acts_as_taggable style system) with "Dining Room", the only Users returned from some_user.boats.first.users should be Users with tickets tagged "Dining Room".
Just for the record, I'm not trying to design something to be insane from the getgo - I'm trying to wedge this arbitrary grouping into a (mostly) existent system.
So we've got:
class User
has_many :tickets
has_many :boats, :through => :tickets
end
class Ticket
belongs_to :user
belongs_to :boat
end
class Boat
has_many :tickets
has_many :users, :through => :tickets
end
Initially, I thought that I could conditionally modify the virtual class like:
singleton = class << a_user_instance ; self ; end
singleton.class_eval(<<-code
has_many :tickets, :include => :tags, :conditions => ['tags.id in (?)', [#{tag_ids.to_s(:db)}]]
code
)
That gets all the way down to generating the SQL, but when generated, it generates SQL ending in:
LEFT OUTER JOIN "tags" ON ("tags"."id" = "taggings"."tag_id") WHERE ("tickets"._id = 1069416589 AND (tags.id in (5001,4502)))
I've tried digging around the ActiveRecord code, but I can't find anywhere that would prefix that 'id' in the SQL above with an underscore. I know that associations are loaded when an ActiveRecord class is loaded, and I'd assume the same with a singleton class. shrug.
I also used an alias_method_chain like:
singleton = class << a_user_instance ; self ; end
singleton.class_eval(<<-code
def tickets_with_tag_filtering
tags = Tag.find(etc, etc)
tickets_without_tag_filtering.scoped(:include => :tags, :conditions => {:'tags.id' => tags})
end
alias_method_chain :tickets, :tag_filtering
code
)
But while that approach produces the desired Tickets, any joins on those tickets use the conditions in the class, not the virtual class. some_user.boats.first.users returns all users.
Any type of comment will be appreciated, especially if I'm barking up the wrong tree with this approach. Thanks!
So a wild guess about your underscore issue is that Rails is generating the assocation code based on the context at the time of evaluation. Being in a singleton class could mess this up, like so:
"#{owner.table_name}.#{association.class.name}_id = #{association.id}"
You could get in there and define a class name property on your singleton class and see if that fixes the issue.
On the whole I don't recommend this. It creates behavior that is agonizing to track down and impossible to extend effectively. It creates a landmine in the codebase that will wound you or someone you love at a later time.
Instead, consider using a named_scope declaration:
class User
has_many :taggings, :through => :tickets
named_scope :visible_to, lambda { |looking_user|
{ :include => [ :tickets, :taggings ],
:conditions => [ "tickets.boat_id in (?) and taggings.ticket_id = tickets.id and taggings.tag_id in (?)", looking_user.boat_ids, looking_user.tag_ids ]
}
}
end
While you may have to go back and edit some code, this is much more flexible in the ways it can be used:
Boat.last.users.visible_to( current_user )
It's clear that a restriction is being placed on the find, and what the purpose of that restriction is. Because the conditions are dynamically calculated at runtime, you can deal with the next weird modification your client hits you with. Say some of their users have xray vision and clairvoyance:
class User
named_scope :visible_to, lambda { |looking_user|
if looking_user.superhuman?
{}
else
{ :include => [ :tickets, :taggings ],
:conditions => [ "tickets.boat_id in (?) and taggings.ticket_id = tickets.id and taggings.tag_id in (?)", looking_user.boat_ids, looking_user.tag_ids ]
}
end
}
end
By returning an empty hash, you can effectively nullify the effect of the scope.
Why not just grab all users on the boat and include their tags.
Then run a quick filter to include & return only the users with the same tag as the inquiring user.
What version of Rails are you using? Have you tried upgrading to see if the underscore issue is fixed? It's like it can't find the foreign key to put in as "tag_id" or somethin'.
My ruby-fu is limited, so I'm not sure how to dynamically include the correct method options at run-time.
Just to help you clarify, you have to worry about this two places. You want to filter a user's viewable users so they only see users with the same tags. Your structure is:
user <--> tickets <--> boats <--> tickets <--> users
... right?
So, you need to filter both sets of tickets down to the ones with the current_user's tags.
Maybe you just need a current_user.viewable_users() method and then filter everything through that? I'm not sure what existing functionality you've got to preserve.
Blech, I don't feel like I'm helping you at all. Sorry.
Your approach is the problem. I know it seems expedient at the moment to hack something in where you don't have to refactor the existing call sites, but I believe given time this will come back to haunt you as the source of bugs and complexity.
Sleeping dogs that lie come back to bite you hard, in my experience. Typically in the form of a future developer who doesn't know your association is "magic" and uses it assuming it's just pail ole rails. He/she likely won't even have a reason to write a test case that would expose the behavior either, which raises the odds you'll only find out about the bug when it's live in production and the client is unhappy. Is it really worth the time you're saving now?
Austinfrombostin is pointing the way. Different semantics? Different names. Rule number one is always to write code that says what it does as clearly as possible. Anything else is the path of madness.