Quick question about eager loading. I have the following code:
#user =
User.includes(:restaurants).find_by_unique_identifier(params[:unique_identifier])
However, I only want to load restaurants associated with a given user only if the restaurants have a list_id of X (which is one of the columns of the restaurants table).
How would I go about this?
I tried the following, but it still loaded all the restaurant records associated with the user.
#user = User.includes(:restaurants).where(:restaurants => {:list_id => params[:list_id]}).find_by_unique_identifier(params[:unique_identifier])
Assuming you have all the associations requirements setup, then you can use joins:
#user = User.all(:conditions =>["restaurants.list_id = ?", params[:list_id] ], :joins => [:restaurants])
UPDATE:
My code fetches a list of users. However, You can use your filtering methods to narrow down the list or get the individual records.
Related
I'm trying to add an advanced search option to my app in which the user can search for certain links based on attributes from 3 different models.
My app is set up so that a User has_many :websites, Website has_many :links, and Link has_many :stats
I know how create SQL queries with joins or includes etc in Rails but I'm getting stuck since I only want to retrieve the latest stat for each link and not all of them - and I don't know the most efficient way to do this.
So for example, let's say a user has 2 websites, each with 10 links, and each link has 100 stats, that's 2,022 objects total, but I only want to search through 42 objects (only 1 stat per link).
Once I get only those 42 objects in a database query I can add .where("attribute like ?", user_input) and return the correct links.
Update
I've tried adding the following to my Link model:
has_many :stats, dependent: :destroy
has_many :one_stat, class_name: "Stat", order: "id ASC", limit: 1
But this doesn't seem to work, for example if I do:
#links = Link.includes(:one_stat).all
#links.each do |l|
puts l.one_stat.size
end
Instead of getting 1, 1, 1... I get the number of all the stats: 125, 40, 76....
Can I use the limit option to get the results I want or does it not work that way?
2nd Update
I've updated my code according to Erez's advice, but still not working properly:
has_one :latest_stat, class_name: "Stat", order: "id ASC"
#links = Link.includes(:latest_stat)
#links.each do |l|
puts l.latest_stat.indexed
end
=> true
=> true
=> true
=> false
=> true
=> true
=> true
Link.includes(:latest_stat).where("stats.indexed = ?", false).count
=> 6
Link.includes(:latest_stat).where("stats.indexed = ?", true).count
=> 7
It should return 1 and 6, but it's still checking all the stats rather than the latest only.
Sometimes, you gotta break through the AR abstraction and get your SQL on. Just a tiny bit.
Let's assume you have really simple relationships: Website has_many :links, and Link belongs_to :website and has_many :stats, and Stat belongs_to :link. No denormalization anywhere. Now, you want to build a query that finds, all of their links, and, for each link, the latest stat, but only for stats with some property (or it could be websites with some property or links with some property).
Untested, but something like:
Website
.includes(:links => :stats)
.where("stats.indexed" => true)
.where("stats.id = (select max(stats2.id)
from stats stats2 where stats2.link_id = links.id)")
That last bit subselects stats that are part of each link and finds the max id. It then filters out stats (from the join at the top) that don't match that max id. The query returns websites, which each have some number of links, and each link has just one stat in its stats collection.
Some extra info
I originally wrote this answer in terms of window functions, which turned out to be overkill, but I think I should cover it here anyway, since, well, fun. You'll note that the aggregate function trick we used above only works because we're determining which stat to use based on its ID, which exactly the property we need to filter the stats from the join by. But let's say you wanted only the first stat as ranked by some criteria other than ID, such as as, say, number_of_clicks; that trick won't work anymore because the aggregation loses track of the IDs. That's where window functions come in.
Again, totally untested:
Website
.includes(:links => :stats)
.where("stats.indexed" => true)
.where(
"(stats.id, 1) in (
select id, row_number()
over (partition by stats2.id order by stats2.number_of_clicks DESC)
from stat stats2 where stats2.link_id = links.id
)"
)
That last where subselects stats that match each link and order them by number_of_clicks ascending, then the in part matches it to a stat from the join. Note that window queries aren't portable to other database platforms. You could also use this technique to solve the original problem you posed (just swap stats2.id for stats2.number_of_clicks); it could conceivably perform better, and is advocated by this blog post.
I'd try this:
has_one :latest_stat, class_name: "Stat", order: "id ASC"
#links = Link.includes(:latest_stat)
#links.each do |l|
puts l.latest_stat
end
Note you can't print latest_stat.size since it is the stat object itself and not a relation.
Is this what you're looking for?
#user.websites.map { |site| site.links.map { |link| link.stats.last } }.flatten
For a given user, this will return an array with that contains the last stats for the links on that users website.
Simply running
ElectricityProfile.find_each do |ep|
if UserProfile.exists?(ep.owner_id) && ep.owner_type == 'UserProfile'
ElectricityProfileSummary.create(ep)
end
end
Takes ages (5 hours) to populate the table. Is there any better way to populate the DB?
Lets say get all the data from the DB and store it in array, hash, etc and then push to create a DB
ElectricityProfile.find_each do |ep|
if UserProfile.exists?(ep.owner_id) && ep.owner_type == 'UserProfile'
array_of_electricity_profiles.push(ep)
end
end
ElectricityProfileSummary.mass_create(ep) # => or any other method :)
Sorry forgot mention I do have overridden method create, that takes multiple models and creates ElectricityProfileSummary...
create!(:owner_id => electricity_profile.owner_id,
:owner_type => electricity_profile.owner_type,
:property_type => electricity_profile.owner.user_property_type,
:household_size => electricity_profile.owner.user_num_of_people,
:has_swimming_pool => electricity_profile.has_swimming_pool,
:bill => electricity_bill,
:contract => electricity_profile.on_contract,
:dirty => true,
:provider => electricity_profile.supplier_id,
:plan => electricity_profile.plan_id,
:state => state,
:postcode => postcode,
:discount => discount,
:has_air_conditioner => electricity_profile.has_air_conditioner,
:has_electric_hot_water => electricity_profile.has_electric_hot_water,
:has_electric_central_heating => electricity_profile.has_electric_central_heating,
:has_electric_cooktup => electricity_profile.has_electric_cooktup
)
Doing this in a stored procedure or raw SQL would probably be the best way to go since ActiveRecord can be very expensive when dealing with that many records. However, you can speed it up quite a bit by using includes or joins.
It looks like you only want to create ElectricityProfileSummary models. I am a little unsure of how your relationships look, but assuming you have the following:
class ElectricityProfile
belongs_to :owner, polymorphic: true
end
class UserProfile
has_many :electricity_profiles, as: owner
end
... you should be able to do something like this:
ElectricityProfile.includes(:owner).each do |ep|
ElectricityProfileSummary.create(ep)
end
Now, I am basing this on the assumption that you are using a polymorphic relationship between ElectricityProfile and UserProfile. If that is not the case, let me know. (I made the assumption because you have owner_id and owner_type, which as a pair make up the two fields necessary for polymorphic relationships.)
Why is using an includes better? Using includes causes ActiveRecord to eager load the relationship between the two models, so you're not doing n+1 queries like you are now. Actually, because you are creating records based on the number of ElectricityProfile records, you're still doing n+1, but what you are doing now is more expensive than n+1 because you are querying UserProfile for every single ElectricityProfile, and then you are querying UserProfile again when creating the ElectricityProfileSummary because you are lazy loading the relationship between EP and UP.
When you do includes, Rails will use an inner join to query between the two tables. Using an inner join eliminates the necessity to do ensure that the UserProfile exists, since the inner join will only return records where both sides of the relationship exist.
If you could wrap your import loop into one transaction block, it should speed up import immensely. Read on about ROR transactions here.
I've got a model (a Feature) that can have many Assets. These Assets each have an issue_date. I'm struggling with what seems like a simple ActiveRecord query to find all Features and their Assets with an issue_date of tomorrow, regardless of if there are Assets or not — preferably with one query.
Here's my query right now.
Feature.includes(:assets).where(:assets => { :issue_date => Date.tomorrow })
Unfortunately, this returns only the Features that have Assets with an issue_date of tomorrow. Even stranger, the generated SQL looks like this (tomorrow's obviously the 19th).
SELECT `features`.* FROM `features` WHERE `assets`.`issue_date` = '2011-08-19'
Shouldn't this have an LEFT JOIN in there somewhere? That's the sort of thing I'm going for. Using joins instead of includes does an INNER JOIN, but that's not what I want. Strangely enough, it seems like I'm getting an INNER JOIN-type of behavior. When I run that includes query above, the actual SQL that's spit out looks something like this...
SELECT `features`.`id` AS t0_r0, `features`.`property_id` AS t0_r1,
// every other column from features truncated for sanity
`assets`.`feature_id` AS t1_r1, `assets`.`asset_type` AS t1_r2,
// all other asset columns truncated for sanity
FROM `features`
LEFT OUTER JOIN `assets` ON `assets`.`feature_id` = `features`.`id`
WHERE `assets`.`issue_date` = '2011-08-19'
Which looks like it should work right but it doesn't. I get only the Features that have Assets with an issue_date of tomorrow. Any idea what I'm doing wrong?
I've tried the older, Rails v2 way of doing it…
Feature.find(:all,
:include => :assets,
:conditions => ['assets.issue_date = ?', Date.tomorrow])
Which gives me the same results. There's one Feature I know that doesn't have any Assets for tomorrow, and it's not in that list.
I've also poked around and found similar questions, but I couldn't seem to find one that explained this opposite behavior I'm seeing.
Edit: I'm so close. This gets me all the Feature objects.
Feature.joins("LEFT OUTER JOIN assets on assets.feature_id = feature.id AND asset.issue_date = #{Date.tomorrow}")
It does not, however, get me the matching Assets bundled into the object. With feature as a returned item in the query, feature.assets makes another call to the database, which I don't want. I want feature.assets to return only those I've specified in that LEFT OUTER JOIN call. What else do I need to do to my query?
I thought this would get me what I needed, but it doesn't. Calling feature.assets (with feature as an item returned in my query) does another query to look for all assets related to that feature.
Feature.joins("LEFT OUTER JOIN assets on assets.feature_id = feature.id AND asset.issue_date = #{Date.tomorrow}")
So here's what does work. Seems a little cleaner, too. My Feature model already has a has_many :assets set on it. I've set up another association with has_many :tomorrows_assets that points to Assets, but with a condition on it. Then, when I ask for Feature.all or Feature.name_of_scope, I can specify .includes(:tomorrows_assets). Winner winner, chicken dinner.
has_many :tomorrows_assets,
:class_name => "Asset",
:readonly => true,
:conditions => "issue_date = '#{Date.tomorrow.to_s}'"
I can successfully query Features and get just what I need included with it, only if it matches the specified criteria (and I've set :readonly because I know I'll never want to edit Assets like this). Here's an IRB session that shows the magic.
features = Feature.includes(:tomorrows_assets)
feature1 = features.find_all{ |f| f.name == 'This Feature Has Assets' }.first
feature1.tomorrows_assets
=> [#<Asset id:1>, #<Asset id:2>]
feature2 = features.find_all{ |f| f.name == 'This One Does Not' }.first
feature2.tomorrows_assets
=> []
And all in only two SQL queries.
I had a very similar problem and managed to solve it using the following query;
Feature.includes(:assets).where('asset.id IS NULL OR asset.issue_date = ?', Date.tomorrow)
This will load all features, regardless of whether it has any assets. Calling feature.asset will return an array of assets if available without running another query
Hope that helps someone!
You have to specify the SQL for outer joins yourself, the joins method only uses inner joins.
Feature.joins("LEFT OUTER JOIN assets ON assets.feature_id = features.id").
where(:assets => {:issue_date => Date.tomorrow})
Have you tried:
Feature.joins( :assets ).where( :issue_date => Date.tomorrow );
The guide here suggests the includes method is used to reduce the number of queries on a secondary table, rather than to join the two tables in the way you're attempting.
http://guides.rubyonrails.org/active_record_querying.html
I want to delete some users and duplicate tags that are in my db. Is there a way I can use rails console to list all of these objects so I can pinpoint each one to delete them. They are not necessarily the last entries?
Assuming your model is derived from ActiveRecord::Base and named User, you can do
with rails console
pp User.all # all users
or
pp User.all(:conditions => {:firstname => 'fred'}) # use hash conditions
or
pp User.all(:conditions => "lastname LIKE 'jenkin%'") # use custom sql conditions
and having the right user (say, id 42), you can do
User.delete(42)
That pp stands for pretty print. Another sometimes handy is y which prints stuff in Yaml format.
This is probably something very simple but I'm looking for the optimal way of retrieving all Products by Tag, so to speak. This is with Spree, so I should stick to the way they have modeled their data. It's actually Product and Taxon (like category, brand, etc.)
So if Product has_and_belongs_to_many :taxons and Taxon has_and_belongs_to_many :products, what's the best way to find all products by a Taxon?
Something like:
#taxon = Taxon.find_by_permalink('categories/')
#products = Product.find_by_taxon(#taxon)
... but I'm not sure what goes into that last method (just made up the name).
Probably you're going to just simply say if there's only one Taxon
#products = #taxon.products
If there's multiple we require a slightly different method. But even then you could just
#products = #taxons.inject([]) {|taxon| taxon.products}
#taxon = Taxon.find_by_permalink('categories', :include => :products)
This will eager-load the products so you can access them through
#taxon.products
without it hitting the database again. This is the more efficient form of just using .products that avoids N+1 query problems.
Won't Taxon.find_by_permalink('categories/').products suffice?
EDIT: Oh and for multiple taxons you could try something like this:
Product.find(:all, :include => :products_taxons, :conditions => { :products_taxons => {:taxon_id => [1,2,3]} }) # will find products with taxons with id 1, 2 or 3
I was able to get this working in Spree 2.1.0.beta with the following customizations:
Based on the answer here: Finding records with two specific records in another table
I added a new product scope in /app/models/spree/product_decorator.rb
Spree::Product.class_eval do
add_search_scope :in_all_taxons do |*taxons|
taxons = get_taxons(taxons)
id = arel_table[:id]
joins(:taxons).where(spree_taxons: { id: taxons }).group(id).having(id.count.eq(taxons.size))
end
end
Then used the new scope by adding it to /app/models/spree/base_decorator.rb
Spree::Core::Search::Base.class_eval do
def get_base_scope
base_scope = Spree::Product.active
base_scope = base_scope.in_all_taxons(taxon) unless taxon.blank?
base_scope = get_products_conditions_for(base_scope, keywords)
base_scope = add_search_scopes(base_scope)
base_scope
end
end
Now I can use the standard search helper to retrieve products (which means I can still supply keywords, etc along with the multiple taxons):
# taxon_ids is an array of taxon ids
#searcher = build_searcher(params.merge(:taxon => taxon_ids))
#products = #searcher.retrieve_products
This works for me and felt pretty painless. However, I'm open to better options.
If you want to find a product by its tags you can use tagged_with
Example
Spree::Product.tagged_with("example")
Will return the products with the tag "example"
Source: https://github.com/mbleigh/acts-as-taggable-on