I have a model Leagues::FantasyPlayer which has a polymorphic variable player_entity which is either a Players::NflPlayer or Players::TeamPlayer.
I'm attempting to load a league's fantasy players, sorted by "average_draft_position." Both tables Players::NflPlayer and Players::TeamPlayer have a column "average_draft_position."
Here is my current attempt:
fantasy_players = paginate Leagues::FantasyPlayer.includes(player_entity: :team).
joins("LEFT JOIN players_nfl_players ON leagues_fantasy_players.player_entity_id = players_nfl_players.id AND leagues_fantasy_players.player_entity_type = 'Players::NflPlayer'").
joins("LEFT JOIN players_team_players ON leagues_fantasy_players.player_entity_id = players_team_players.id AND leagues_fantasy_players.player_entity_type = 'Players::TeamPlayer'").
where(available: true, conference_id: conference_id,league_id: league_id).
order("players_nfl_players.average_draft_position, players_team_players.average_draft_position"), per_page: 15
The problem is that this returns the Players::NflPlayer table sorted by average_draft_position first, and then Players::TeamPlayer table sorted be average_draft_position afterwards - is there some way I can have the results from the two different tables interleaved?
Thank you!!
This should do the trick.
.order('COALESCE(players_nfl_players.average_draft_position, players_team_players.average_draft_position) DESC')
Related
Problem:
I am using the ransack gem to sort columns in a table. I have 2 models: Campaign and Course. A campaign has many courses, and a course belongs to one campaign. Each course has a number of total_attendees. My Campaigns table has a column for Total Attendees, and I want it to be sortable. So it would sum up the total_attendees field for each course that belongs to a single campaign, and sort based on that sum.
Ex. A campaign has 3 courses, each with 10 attendees. The Total Attendees column on the campaign table would show 30 and it would be sortable against total attendees for all the other campaigns.
I found ransackers:
https://github.com/activerecord-hackery/ransack/wiki/Using-Ransackers
and this SO question: Ransack sort by sum of relation
and from that put together a lot of what is below.
From Model - campaign.rb:
class Campaign < ApplicationRecord
has_many :courses
ransacker :sum_of_total_attendees do
query = "SELECT SUM(r.total_attendees)
FROM campaigns c
LEFT OUTER JOIN courses r
ON r.campaign_id = c.id
GROUP BY c.id"
Arel.sql(query)
end
end
From Model - course.rb:
class Course < ApplicationRecord
belongs_to :campaign, optional: true
end
View:
<th scope="col"><%= sort_link(#q, :sum_of_total_attendees, 'Total Attendees') %></th>
Controller - campaigns_controller.rb:
all_campaigns = Campaign.all
#q = all_campaigns.ransack(params[:q])
#campaigns = #q.result
Errors:
The ransacker query gives me the data I want, but I don't know what to do to get the right information .
Originally, when I clicked on the th link to sort the data, I got this error:
PG::CardinalityViolation: ERROR: more than one row returned by a
subquery used as an expression
I don't know what changed, but now I'm getting this error:
PG::SyntaxError: ERROR: syntax error at or near "SELECT"
LINE 1: SELECT "campaigns".* FROM "campaigns" ORDER BY SELECT SUM(r....
^
: SELECT "campaigns".* FROM "campaigns" ORDER BY SELECT
SUM(r.total_attendees)
FROM campaigns c
LEFT OUTER JOIN courses r
ON r.campaign_id = c.id
GROUP BY c.id ASC
This error seems to say that the ransack search parameter, #q and the ransacker query don't work together. There are two selects in this request, when there should definitely be only one, but the first one is coming from ransack, so I'm not sure how to address it.
How do I get my query to sort correctly with ransack?
Articles I've looked at but did not seem to apply to what I was looking to accomplish with this story:
Ransack Sort By Sum of Relation: This is the one I worked from a lot, but I'm not sure why it works for this user and not for me. They don't show what is changed, if anything, in the controller
Ransack Github Issue For Multiple Params: This doesn't cover the issue of summing table columns.
Rails Ransack Sorting Searching Based On A Definition In The Model: This didn't apply to my need to sort based on summed data.
Three Ways to Bend The Ransack Gem: This looks like what I was doing, but I'm not sure why theirs is working but mine isn't.
I am making scopes for a model that looks something like this:
class PressRelease < ActiveRecord::Base
has_many :publications
end
What I want to get is all press_releases that does not have publications, but from a scope method, so it can be chained with other scopes. Any ideas?
Thanks!
NOTE: I know that there are methods like present? or any? and so on, but these methods does not return an ActiveRecord::Relation as scope does.
NOTE: I am using RoR 3
Avoid eager_loading if you do not need it (it adds overhead). Also, there is no need for subselect statements.
scope :without_publications, -> { joins("LEFT OUTER JOIN publications ON publications.press_release_id = press_releases.id").where(publications: { id: nil }) }
Explanation and response to comments
My initial thoughts about eager loading overhead is that ActiveRecord would instantiate all the child records (publications) for each press release. Then I realized that the query will never return press release records with publications. So that is a moot point.
There are some points and observations to be made about the way ActiveRecord works. Some things I had previously learned from experience, and some things I learned exploring your question.
The query from includes(:publications).where(publications: {id: nil}) is actually different from my example. It will return all columns from the publications table in addition to the columns from press_releases. The publication columns are completely unnecessary because they will always be null. However, both queries ultimately result in the same set of PressRelease objects.
With the includes method, if you add any sort of limit, for example chaining .first, .last or .limit(), then ActiveRecord (4.2.4) will resort to executing two queries. The first query returns IDs, and the second query uses those IDs to get results. Using the SQL snippet method, ActiveRecord is able to use just one query. Here is an example of this from one of my applications:
Profile.includes(:positions).where(positions: { id: nil }).limit(5)
# SQL (0.8ms) SELECT DISTINCT "profiles"."id" FROM "profiles" LEFT OUTER JOIN "positions" ON "positions"."profile_id" = "profiles"."id" WHERE "positions"."id" IS NULL LIMIT 5
# SQL (0.8ms) SELECT "profiles"."id" AS t0_r0, ..., "positions"."end_year" AS t1_r11 FROM "profiles" LEFT OUTER JOIN "positions" ON "positions"."profile_id" = "profiles"."id" # WHERE "positions"."id" IS NULL AND "profiles"."id" IN (107, 24, 7, 78, 89)
Profile.joins("LEFT OUTER JOIN positions ON positions.profile_id = profiles.id").where(positions: { id: nil }).limit(5)
# Profile Load (1.0ms) SELECT "profiles".* FROM "profiles" LEFT OUTER JOIN positions ON positions.profile_id = profiles.id WHERE "positions"."id" IS NULL LIMIT 5
Most importantly
eager_loading and includes were not intended to solve the problem at hand. And for this particular case I think you are much more aware of what is needed than ActiveRecord is. You can therefore make better decisions about how to structure the query.
you can de the following in your PressRelease:
scope :your_scope, -> { where('id NOT IN(select press_release_id from publications)') }
this will return all PressRelease record without publications.
Couple ways to do this, first one requires two db queries:
PressRelease.where.not(id: Publications.uniq.pluck(:press_release_id))
or if you don't want to hardcode association foreign key:
PressRelease.where.not(id: PressRelease.uniq.joins(:publications).pluck(:id))
Another one is to do a left join and pick those without associated elements - you get a relation object, but it will be tricky to work with it as it already has a join on it:
PressRelease.eager_load(:publications).where(publications: {id: nil})
Another one is to use counter_cache feature. You will need to add publication_count column to your press_releases table.
class Publications < ActiveRecord::Base
belongs_to :presss_release, counter_cache: true
end
Rails will keep this column in sync with a number of records associated to given mode, so then you can simply do:
PressRelease.where(publications_count: [nil, 0])
There are two models with our familiar one-to-many relationship:
class Custom
has_many :orders
end
class Order
belongs_to :custom
end
I want to do the following work:
get all the custom information whose age is over 18, and how many big orders(pay for 1,000 dollars) they have?
UPDATE:
for the models:
rails g model custom name:string age:integer
rails g model orders amount:decimal custom_id:integer
I hope one left join sql statement will do all my job, and don't construct unnecessary objects like this:
Custom.where('age > ?', '18').includes(:orders).where('orders.amount > ?', '1000')
It will construct a lot of order objects which I don't need, and it will calculate the count by Array#count function which will waste time.
UPDATE 2:
My own solution is wrong, it will remove customs who doesn't have big orders from the result.
Finding adult customers with big orders
This solution uses a single query, with the nested orders relation transformed into a sub-query.
big_customers = Custom.where("age > ?", "18").where(
id: Order.where("amount > ?", "1000").select(:custom_id)
)
Grab all adults and their # of big orders (MySQL)
This can still be done in a single query. The count is grabbed via a join on orders and sticking the count of orders into a column in the result called big_orders_count, which ActiveRecord turns into a method. It involves a lot more "raw" SQL. I don't know any way to avoid this with ActiveRecord except with the great squeel gem.
adults = Custom.where("age > ?", "18").select([
Custom.arel_table["*"],
"count(orders.id) as big_orders_count"
]).joins(%{LEFT JOIN orders
ON orders.custom_id = customs.id
AND orders.amount > 1000})
# see count:
adults.first.big_orders_count
You might want to consider caching counters like this. This join will be expensive on the database, so if you had a dedicated customs.big_order_count column that was either refreshed regularly or updated by an observer that watches for big Order records.
Grab all adults and their # of big orders (PostgreSQL)
Solution 2 is mysql only. To get this to work in postgresql I created a third solution that uses a sub-query. Still one call to the DB :-)
adults = Custom.where("age > ?", "18").select([
%{"customs".*},
%{(
SELECT count(*)
FROM orders
WHERE orders.custom_id = customs.id
AND orders.amount > 1000
) AS big_orders_count}
])
# see count:
adults.first.big_orders_count
I have tested this against postgresql with real data. There may be a way to use more ActiveRecord and less SQL, but this works.
Edited.
#custom_over_18 = Custom.where("age > ?", "18").orders.where("amount > ?", "1000").count
I have a model offers and another historical_offers, one offer has_many historical_offers.
Now I would like to eager load the historical_offers of one given day for a set of offers, if it exists. For this, I think I need to pass the day to the ON clause, not the WHERE clause, so that I get all offers, also when there is no historical_offer for the given day.
With
Offer.where(several_complex_conditions).includes(:historical_offers).where("historical_offers.day = ?", Date.today)
I would get
SELECT * FROM offers
LEFT OUTER JOIN historical_offers
ON offers.id = historical_offers.offer_id
WHERE day = '2012-11-09' AND ...
But I want to have the condition in the ON clause, not in the WHERE clause:
SELECT * FROM offers
LEFT OUTER JOIN historical_offers
ON offers.id = historical_offers.offer_id AND day = '2012-11-09'
WHERE ...
I guess I could alter the has_many definition with a lambda condition for a specific date, but how would I pass in a date then?
Alternatively I could write the joins mysqlf like this:
Offer.where(several_complex_conditions)
.joins(["historical_offers ON offers.id = historical_offers.offer_id AND day = ?", Date.today])
But how can I hook this up so that eager loading is done?
After a few hours headscratching and trying all sorts of ways to accomplish eager loading of a constrained set of associated records I came across #dbenhur's answer in this thread which works fine for me - however the condition isn't something I'm passing in (it's a date relative to Date.today). Basically it is creating an association with the conditions I wanted to put into the LEFT JOIN ON clause into the has_many condition.
has_many :prices, order: "rate_date"
has_many :future_valid_prices,
class_name: 'Price',
conditions: ['rate_date > ? and rate is not null', Date.today-7.days]
And then in my controller:
#property = current_agent.properties.includes(:future_valid_prices).find_by_id(params[:id])
I want to join records together and separate them with "-"
I know how to join one table records together like this:
#keywords = #tweet.hash_tags.join("-")
But what if it's HABTM associated tables.
For example.
// BRAND MODEL
has_and_belongs_to_many :categories
// CATEGORY MODEL
has_and_belongs_to_many :brands
If I do this:
#brands = Brand.all
#brand_categories = #brands.categories.join("-")
I get this result:
#<Category:0x0000010445c928>,#<Category:0x0000010445c7c0>,#<Category:0x0000010445c5e0>,#<Category:0x0000010445c400>,#<Category:0x0000010445c270>
Hope you understand my question - thanks.
#join will call #to_s on the items in the Array returned by #brands.categories by default, and it doesn't look like you've defined a custom Category#to_s. Either do so, or be more explicit about the string representation you want; if, for example, a Category has a title attribute, you could use:
#brands_categories = #brands.categories.map(&:title).join("-")
Assuming your Category table has a name field:
#brand_categories = #brands.categories.collect(&:name).join("-")
This will put all of the name values into an array, and then join those.