In my RoR application, I've got a database lookup similar to this one:
Client.joins(:products).where({'product.id' => [1,2,3]})
Unfortunately this will return all clients that have bought product 1, 2 or 3 but I only want to get back the clients, that bought all of the three products. In other words, I'd like to write a query that matches for n elements in a given set.
Are there any elegant solutions for this?
This is not really elegant. But it should translate into the needed SQL.
Client.joins(:products).
where({'products.id' => [1,2,3]}).
group('users.id').
having('COUNT(DISTINCT products.id) >= 3')
Same answer with more dynamic way
ids = [1,2,3]
Client.joins(:products).
where({'products.id' => ids}).
group('users.id').
having('COUNT(DISTINCT products.id) >= ?', ids.size)
Related
I have following SQL Query:
SELECT campaigns.* , campaign_countries.points, offers.image
FROM campaigns
JOIN campaign_countries ON campaigns.id = campaign_countries.campaign_id
JOIN countries ON campaign_countries.country_id = countries.id
JOIN offers ON campaigns.offer_id = offers.id
WHERE countries.code = 'US'
This works perfectly well. I want its rails active record version some thing like:
Campaign.includes(campaign_countries: :country).where(countries: {code: "US"})
Above code runs more or less correct query (did not try to include offers table), issue is returned result is collection of Campaign objects so obviously it does not include Points
My tables are:
campaigns --HAS_MANY--< campaign_countries --BELONGS_TO--< countries
campaigns --BELONGS_TO--> offers
Any suggestions to write AR version of this SQL? I don't want to use SQL statement in my code.
I some how got this working without SQL but surely its poor man's solution:
in my controller I have:
campaigns = Campaign.includes(campaign_countries: :country).where(countries: {code: country.to_s})
render :json => campaigns.to_json(:country => country)
in campaign model:
def points_for_country country
CampaignCountry.joins(:campaign, :country).where(countries: {code: country}, campaigns: {id: self.id}).first
end
def as_json options={}
json = {
id: id,
cid: cid,
name: name,
offer: offer,
points_details: options[:country] ? points_for_country(options[:country]) : ""
}
end
and in campaign_countries model:
def as_json options={}
json = {
face_value: face_value,
actual_value: actual_value,
points: points
}
end
Why this is not good solution? because it invokes too many queries:
1. It invokes query when first join is performed to get list of campaigns specific to country
2. For each campaign found in first query it will invoke one more query on campaign_countries table to get Points for that campaign and country.
This is bad, Bad and BAD solution. Any suggestions to improve this?
If You have campaign, You can use campaign.campaign_countries to get associated campaign_countries and just get points from them.
> campaign.campaign_countries.map(&:points)
=> [1,2,3,4,5]
Similarly You will be able to get image from offers relation.
EDIT:
Ok, I guess now I know what's going on. You can use joins with select to get object with attached fields from join tables.
cs = Campaign.joins(campaign_countries: :country).joins(:offers).select('campaigns.*, campaign_countries.points, offers.image').where(countries: {code: "US"})
You can than reference additional fields by their name on Campaign object
cs.first.points
cs.first.image
But be sure, that additional column names do not overlap with some primary table fields or object methods.
EDIT 2:
After some more research I came to conclusion that my first version was actually correct for this case. I will use my own console as example.
> u = User.includes(:orders => :cart).where(:carts => { :id => [5168, 5167] }).first
> u.orders.length # no query is performed
=> 2
> u.orders.count # count query is performed
=> 5
So when You use includes with condition on country, in campaign_countries are stored only campaign_countries that fulfill Your condition.
Try this:
Campaign.joins( [{ :campaign_countries => :countries}, :offers]).where('`countries`.`code` = ?', "US")
I have 2 models - Restaurant and Feature. They are connected via has_and_belongs_to_many relationship. The gist of it is that you have restaurants with many features like delivery, pizza, sandwiches, salad bar, vegetarian option,… So now when the user wants to filter the restaurants and lets say he checks pizza and delivery, I want to display all the restaurants that have both features; pizza, delivery and maybe some more, but it HAS TO HAVE pizza AND delivery.
If I do a simple .where('features IN (?)', params[:features]) I (of course) get the restaurants that have either - so or pizza or delivery or both - which is not at all what I want.
My SQL/Rails knowledge is kinda limited since I'm new to this but I asked a friend and now I have this huuuge SQL that gets the job done:
Restaurant.find_by_sql(['SELECT restaurant_id FROM (
SELECT features_restaurants.*, ROW_NUMBER() OVER(PARTITION BY restaurants.id ORDER BY features.id) AS rn FROM restaurants
JOIN features_restaurants ON restaurants.id = features_restaurants.restaurant_id
JOIN features ON features_restaurants.feature_id = features.id
WHERE features.id in (?)
) t
WHERE rn = ?', params[:features], params[:features].count])
So my question is: is there a better - more Rails even - way of doing this? How would you do it?
Oh BTW I'm using Rails 4 on Heroku so it's a Postgres DB.
This is an example of a set-iwthin-sets query. I advocate solving these with group by and having, because this provides a general framework.
Here is how this works in your case:
select fr.restaurant_id
from features_restaurants fr join
features f
on fr.feature_id = f.feature_id
group by fr.restaurant_id
having sum(case when f.feature_name = 'pizza' then 1 else 0 end) > 0 and
sum(case when f.feature_name = 'delivery' then 1 else 0 end) > 0
Each condition in the having clause is counting for the presence of one of the features -- "pizza" and "delivery". If both features are present, then you get the restaurant_id.
How much data is in your features table? Is it just a table of ids and names?
If so, and you're willing to do a little denormalization, you can do this much more easily by encoding the features as a text array on restaurant.
With this scheme your queries boil down to
select * from restaurants where restaurants.features #> ARRAY['pizza', 'delivery']
If you want to maintain your features table because it contains useful data, you can store the array of feature ids on the restaurant and do a query like this:
select * from restaurants where restaurants.feature_ids #> ARRAY[5, 17]
If you don't know the ids up front, and want it all in one query, you should be able to do something along these lines:
select * from restaurants where restaurants.feature_ids #> (
select id from features where name in ('pizza', 'delivery')
) as matched_features
That last query might need some more consideration...
Anyways, I've actually got a pretty detailed article written up about Tagging in Postgres and ActiveRecord if you want some more details.
This is not "copy and paste" solution but if you consider following steps you will have fast working query.
index feature_name column (I'm assuming that column feature_id is indexed on both tables)
place each feature_name param in exists():
select fr.restaurant_id
from
features_restaurants fr
where
exists(select true from features f where fr.feature_id = f.feature_id and f.feature_name = 'pizza')
and
exists(select true from features f where fr.feature_id = f.feature_id and f.feature_name = 'delivery')
group by
fr.restaurant_id
Maybe you're looking at it backwards?
Maybe try merging the restaurants returned by each feature.
Simplified:
pizza_restaurants = Feature.find_by_name('pizza').restaurants
delivery_restaurants = Feature.find_by_name('delivery').restaurants
pizza_delivery_restaurants = pizza_restaurants & delivery_restaurants
Obviously, this is a single instance solution. But it illustrates the idea.
UPDATE
Here's a dynamic method to pull in all filters without writing SQL (i.e. the "Railsy" way)
def get_restaurants_by_feature_names(features)
# accepts an array of feature names
restaurants = Restaurant.all
features.each do |f|
feature_restaurants = Feature.find_by_name(f).restaurants
restaurants = feature_restaurants & restaurants
end
return restaurants
end
Since its an AND condition (the OR conditions get dicey with AREL). I reread your stated problem and ignoring the SQL. I think this is what you want.
# in Restaurant
has_many :features
# in Feature
has_many :restaurants
# this is a contrived example. you may be doing something like
# where(name: 'pizza'). I'm just making this condition up. You
# could also make this more DRY by just passing in the name if
# that's what you're doing.
def self.pizza
where(pizza: true)
end
def self.delivery
where(delivery: true)
end
# query
Restaurant.features.pizza.delivery
Basically you call the association with ".features" and then you use the self methods defined on features. Hopefully I didn't misunderstand the original problem.
Cheers!
Restaurant
.joins(:features)
.where(features: {name: ['pizza','delivery']})
.group(:id)
.having('count(features.name) = ?', 2)
This seems to work for me. I tried it with SQLite though.
With ActiveRecord you can pass a field and an array into WHERE like so:
Product.joins(:category).where('category.id' => [x,y,z])
(in this case Product has a many to many relationship with Category)
This uses the IN operator to find all products in categories with an ID of x, y, or z
What I would like to do is find all products in categories with an ID of x, y, AND z. I know you can produce this sort of result like so:
Product.joins(:category).where('category.id' => x).where('category.id' => y).where('category.id' => z)
In other words, I want to find products that have all of the categories supplied.
I feel like I could do be doing something much simpler here. Any ideas?
Update: I believe this question is relevant, still having trouble getting it to work. Still think there might be another way to do this.
Havent tried... but something like below should give you hint to get started -
Product.joins(:categories).select("products.*, GROUP_CONCAT('categories.id') as category_ids").group('products.id').having('category_ids = ?', [1,2,3])
How about this:
Product.joins(:category)
.where('category.id = ? AND category.id = ? AND category.id = ?',x,y,z)
I'm doing a rails app. I have to do a comparison engine a bit complex. I'm currently trying to do a prototype. My query can vary widely so i have to work with a lot of scopes, but that's not my problem.
My query have to compare candidates. These candidates have answered some tests. These tests belongs to category. Theses tests have different max value, and i have to be able to compare candidates by categories.
So i have to calculate a % of good answers. I have to be able to compare candidates in all possible use cases in one category. So, i have to be able to compare the average good answer rate for all this category.
In a nutshell : I have to be able to use subqueries in order to compare some candidates. I have to be able to compare them for a test or a category. My problem is using a subquery able to return a good answer rate for all tests a candidats may have passed in a category.
And I have to be able to use this subquery in an order_by or having clause.
How can I construct this subquery ? I have no problem to handle complex conditional queries with some scopes. This has to be a real subquery, because I am working with 6 or 7 models here.
I ask for an active record way, cause this must work with whatever database supported by rails.
Excuse my poor English.
Edit :
An example is worth 1000 words so how could do something like this :
Sessiontest.find(Candidat.where(:firstname => 'toto'))
This example is stupid, ok. So, is it possible to do something like this ?
Edit2 :
I saw some posts about AREL. I wish to know if it is possible to do this without a third party plugin.
Is it possible to do some sub queries in subqueries with arel? Because for example, my number of points per test, is the sum of the points of all his questions. (Sad, but I have to keep it). And I need this, so my subquery can calculate my good answers %.
So you got the idea. That's something, which has to be really powerful, so I need something powerful, and not too much error prone.
Edit3 : I made some progress, but I can't for a while post an answer.
It seem possible to get this work without any plugin. I have some success in buildings some subqueries like this :
toto = Candidat.where(:lastname => Candidat.select(:lastname).where(:lastname => "ulysse").limit(1))
The request :
Candidat Load (1.0ms)[0m SELECT "candidats".* FROM "candidats" WHERE "candidats"."lastname" IN (SELECT "candidats"."id" FROM "candidats" WHERE "candidats"."lastname" = 'ulysse' LIMIT 1
This works and create a real subquery. I will try some more advanced experiences, in order to get the level I actually need.
Just tried sub-subquery works wonder too.
Edit 5 :
I am trying some more advanced things, and there is a lot of things, i still don't understand.
- toto = Candidat.where("id = ? / ? ", Sessiontest.select(:id).where(:id => 6), Sessiontest.select(:id).where(:id => 2))
This is just a stupid example in order to get an object with an id of 3. This code works, but not as i expected.
See, the sql :
1m[35m (1.0ms)[0m SELECT COUNT("sessiontests"."id") FROM "sessiontests" WHERE "sessiontests"."id" = 6
[1m[36mSessiontest Load (0.0ms)[0m [1mSELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 6[0m
[1m[35m (1.0ms)[0m SELECT COUNT("sessiontests"."id") FROM "sessiontests" WHERE "sessiontests"."id" = 2
[1m[36mSessiontest Load (1.0ms)[0m [1mSELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 2[0m
[1m[35mCandidat Load (1.0ms)[0m SELECT "candidats".* FROM "candidats" WHERE (id = 6 / 2)
So, it does not use a subqueries. I tried with .to_sql. But it introduce my sql this way :
1m[36mCandidat Load (0.0ms)[0m [1mSELECT "candidats".* FROM "candidats" WHERE (id = 'SELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 6' / 2 )[0m
So active record quoted the subreust for security purpose. this is closer to my wish, but not really what i want.
This does not work
Candidat.where("id = (?) / ? ", Sessiontest.select(:id).where(:id => 6).to_sql, Sessiontest.select(:id).where(:id => 2))
Quotes prevents the subquery to work.
But this work :
Candidat.where("id = (" + Sessiontest.select(:id).where(:id => 6).to_sql + ") / (" + Sessiontest.select(:id).where(:id => 2).to_sql + ") ")
[1m[36mCandidat Load (1.0ms)[0m [1mSELECT "candidats".* FROM "candidats" WHERE (id = (SELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 6) / (SELECT id FROM "sessiontests" WHERE "sessiontests"."id" = 2) )[0m
But I find this ugly. I will try to get these subqueries working in a more dynamic way. I mean replace the integer values by columns name.
I don't have anymore the exact answer to this question, because i do not work in the same enterprise anymore. But the solution to this problem, was to use a group_by clause. So the request became really easy.
With a group_by, i was able to manipulate, category or a technology with ease.
I was hoping somebody may be able to point me in the right direction...
I have a database called Info and use a find command to select the rows in this database which match a certain criteria
#matching = Info.find( :all, :conditions => ["product_name = ?", distinctproduct], :order => 'Price ASC')
I then pull out the cheapest of these items
#cheapest = #matching.first
Finally, I would like to create an instantaneous array which contains a list of #cheapest for a number of different search criteria. i.e. row 1 in #allcheapest is #cheapest for criteria 1, row 2 in #allcheapest is #cheapest for criteria 2, ...
Any help would be great, thanks in advance
Info.where(:product_name => distinct_product.to_s).order('Price ASC').first
to select the cheapest price for the product_name. Without more insight into how your database is structured, it is difficult to suggest how to obtain the latter, but you may try
Info.where(:product_name => distinct_product.to_s).order('Price ASC').group(:product_name)