I'm trying to do some fairly complicated record sorting that I was having a bit of trouble with. I have three models:
class User < ActiveRecord::Base
has_many :registers
has_many :results, :through => :registers
#Find all the Users that exist as registrants for a tournament
scope :with_tournament_entrees, :include => :registers, :conditions => "registers.id IS NOT NULL"
end
Register
class Register < ActiveRecord::Base
belongs_to :user
has_many :results
end
Result
class Result < ActiveRecord::Base
belongs_to :register
end
Now on a Tournament result page I list all users by their total wins (wins is calculated through the results table). First thing first I find all users who have entered a tournament with the query:
User.with_tournament_entrees
With this I can simply loop through the returned users and query each individual record with the following to retrieve each users "Total Wins":
user.results.where("win = true").count()
However I would also like to take this a step further and order all of the users by their "Total Wins", and this is the best I could come up with:
User.with_tournament_entrees.select('SELECT *,
(SELECT count(*)
FROM results
INNER JOIN "registers"
ON "results"."register_id" = "registers"."id"
WHERE "registers"."user_id" = "users.id"
AND (win = true)
) AS total_wins
FROM users ORDER BY total_wins DESC')
I think it's close, but it doesn't actually order by the total_wins in descending order as I instruct it to. I'm using a PostgreSQL database.
Edit:
There's actually three selects taking place, the first occurs on User.with_tournament_entries which just performs a quick filter on the User table. If I ignore that and try
SELECT *, (SELECT count(*) FROM results INNER JOIN "registers" ON "results"."register_id" = "registers"."id" WHERE "registers"."user_id" = "users.id" AND (win = true)) AS total_wins FROM users ORDER BY total_wins DESC;
it fails in both PSQL and the ERB console. I get the error message:
PGError: ERROR: column "users.id" does not exist
I think this happens because the inner-select occurs before the outer-select so it doesn't have access to the user id before hand. Not sure how to give it access to all user ids before than inner select occurs but this isn't an issue when I do User.with_tournament_entires followed by the query.
In your SQL, "users.id" is quoted wrong -- it's telling Postgres to look for a column named, literally, "users.id".
It should be "users"."id", or, just users.id (you only need to quote it if you have a table/column name that conflicts with a postgres keyword, or have punctuation or something else unusual).
Related
I want to show a line chart on the admin page (with chartkick) with the incremental number of scores related to their earliest export date.
I have the following models:
# score.rb
class Score < ApplicationRecord
has_and_belongs_to_many :export_orders, join_table: :scores_export_orders
end
# export_order.rb
class ExportOrder < ApplicationRecord
has_and_belongs_to_many :scores, join_table: :scores_export_orders
end
How do I select, for each Score having at least one ExportOrder, the corresponding ExportOrder with the earliest created_at (in date only format)?
I had a look at this, but my situation has a HABTM relationship instead of a simple has_many.
I tried this code, to get at least a mapping between oldest export date and number of scores:
sql = "
SELECT
COUNT(DISTINCT scores.id), MIN(export_orders.created_at::date)
FROM
scores
INNER JOIN
scores_export_orders
ON
scores.id = scores_export_orders.score_id
INNER JOIN
export_orders
ON
export_orders.id = scores_export_orders.export_order_id
GROUP BY
export_orders.created_at::date
".split("\n").join(' ')
query = ActiveRecord::Base.connection.execute(sql)
query.map { |v| [v['count'], v['min']] }
but the total number of scores is greater than all scores having an export date.
Any ideas?
Try:
class Score < ApplicationRecord
has_and_belongs_to_many :export_orders, join_table: :scores_export_orders
def earliest_export_date
export_orders.pluck(&:created_at).min
end
end
This will let you call #score.earliest_export_date, which should return the value you want.
I also think it's the most performant way to do it in ruby, although someone may correct me on that.
The following has better performance than Mark's solution since it relies on pure SQL. Basically, the GROUP BY clause required grouping by scores_export_orders.score_id rather than export_orders.created_at:
sql = "
SELECT
COUNT(DISTINCT scores_export_orders.score_id), MIN(export_orders.created_at::date)
INNER JOIN
scores_export_orders
INNER JOIN
export_orders
ON
export_orders.id = scores_export_orders.export_order_id
GROUP BY
scores_export_orders.score_id
".split("\n").join(' ')
query = ActiveRecord::Base.connection.execute(sql)
query.map { |v| [v['count'], v['min']] }
I couldn't find an exact equivalent in ActiveRecord instructions (all of such attempts were giving me strange results), so executing the SQL will also do the trick.
I have a user model which has many subscriptions. I need to make two selections:
active users defined as user with a subscription in the last month
inactive users the ones that don't meet the (1) criteria
My subscription model has a simple scope .latest which is defined as ordered("created_at DESC").first.
To make selection (1) I use:
User.joins(:subscriptions).where("subscriptions.created_at > ?", 1.month.ago).distinct
This works, no problem there. However, I can't seem to define a working query for selection (2). Currently I use selection (1) and 'subtract' that from User.all to get the remaining users. This feels a bit like a hack.
The selection I need is:
all users whose most recent subscription was created more than 1 month ago
It's the most recent part of the query that has me stuck.
Any help appreciated.
Quick & dirty way: use complex SQL like this
Assume you are using auto incremental ID
User.select("users.*, MAX(subscriptions.id) as last_subscription_id")
.joins(:subscriptions)
.group("subscriptions.user_id")
.having("last_subscription_id = (select id from subscriptions where user_id=users.id and created_at < '2017-10-01 09:23:28.182475' order by id desc limit 1)")
Recommended way
Add last_subscription_id to users table and setup a belongs_to relationship user belongs_to last_subscription then do the joins normally. You need to update last_subscription_id of an user when new subscription for this user is created too.
Example: User class looks like this (I include has_many :subscriptions to show that we have 2 relations now)
class User < ActiveRecord::Base
has_many :subscriptions
belongs_to :last_subscription, class_name: 'Subscription', foreign_key: :last_subscription_id
end
And query will be
User.joins(:last_subscription).where("subscriptions.created_at < ?", 1.month.ago)
for the most recent part you can do this.
User.joins("LEFT JOIN subscriptions ON subscriptions.user_id = users.id").order("subscriptions.created_at DESC").select("subscriptions.created_at AS max_date").group_by(&:id).select{|key, value| value[0].max_date < 1.month.ago}.values.flatten
I have two models
class User
has_many :subscriptions
end
and
class Subscription
belongs_to :user
end
one one of my pages I would like to display a list of all users ordered by the number of subscriptions each user has. I am not to good with sql queries but I think that
list = Users.all.joins(:subscriptions).group("user.id").order("count(subscriptions.id) DESC")
dose the job. Now to my problem, when I try to count the total number of objects in list, using list.count, I get a hash with user.id and subscription count, like this
{11 => 5,
8 => 7,
1 => 11,
...}
not the total number of users in list.. .count works fine if I have a list sorted by for example user name (which is in the user table). I would really like to use .count since it in a module for pagination thats in a gem but any ideas is great!
Thanks!
We can just use a single query to finish this:
User.joins("LEFT OUTER JOIN ( SELECT user_id, COUNT(*) as num_subscriptions
FROM subscriptions
GROUP BY user_id
) AS temp
ON temp.user_id = users.id")
.order("temp.num_subscriptions DESC")
Basically, my idea is to try to query the number of subscription for each user_id in the subquery, then join with User. I used LEFT OUTER JOIN, because there will be several users which don't have any subscriptions
Improve option: You can define a scope inside User, it would be more beautiful for later usage:
user.rb
class User < ActiveRecord::Base
has_many :subscriptions
scope :sorted_by_num_subscriptions, -> {
joins("LEFT OUTER JOIN ( SELECT user_id, COUNT(*) as num_subscriptions
FROM subscriptions
GROUP BY user_id
) AS temp
ON temp.user_id = users.id")
.order("temp.num_subscriptions DESC")
}
end
Then just use it:
User.sorted_by_num_subscriptions
When grouping, the count method changes it's behavior and indeed, instead of returning the total count of records, it returns a hash of the counts for each group (see the docs for more info). So what you get with list.count is simply a hash of the subscription counts for each user.
So, your query is correct and all you need is to sum up the individual counts in the groups. This can be done simply by:
total_count = list.count.values.sum
If it is the pagination code that calls just a bare count that makes the issue, usually the pagination code is able to accept a parameter with total count. For example, will_paginate accepts the total_entries parameter, so you should be able to pass it the total count like this:
list.paginate(page: 2, total_entries: list.count.values.sum)
I'm having some issues with trying to order a model by association count. The method I'm using was described here and it works in console and whenever I pause it by using byebug. Other times it doesn't execute the select statement at all and just tries to do the group and order. This is my class:
class Course < ActiveRecord::Base
has_many :course_videos, foreign_key: :course_id
has_many :videos, through: :course_videos
scope :ordered_by_video_count, -> {
joins(:videos)
.select("courses.*, count(videos.id) as video_count")
.group("courses.id")
.order("video_count desc")
}
end
And the exact error I'm getting is this:
SQLite3::SQLException: no such column: video_count: SELECT COUNT(*) AS count_all, courses.id AS courses_id FROM "courses" INNER JOIN "course_videos" ON "course_videos"."course_id" = "courses"."id" INNER JOIN "videos" ON "videos"."id" = "course_videos"."video_id" GROUP BY courses.id ORDER BY video_count desc
Thanks!
Stefan
not sure if it makes a difference, but try
.order(video_count: :desc)
that's the syntax I alway use.
I have 2 models, user and centre, which have a many to many relationship.
class User < ActiveRecord::Base
attr_accessible :name
has_and_belongs_to_many :centres
end
class Centre < ActiveRecord::Base
attr_accessible :name, :centre_id, :city_id, :state_id
has_and_belongs_to_many :users
end
Now I have an user with multiple centres, and I want to retrieve all the centres that have the same "state_id" as that user.
This is what I am doing now
state_id_array = []
user.centres.each do |centre|
state_id_array << centre.state_id
end
return Centre.where("state_id IN (?)", state_id_array).uniq
It works, but it's very ugly. Is there a better way for achieving this? Ideally a one line query.
UPDATE
Now I have
Centre.where('centres.state_id IN (?)', Centre.select('state_id').joins(:user).where('users.id=(?)', user))
The subquery work by itself, but when I tried to execute the entire query, I get NULL for the inner query.
Centre.select('state_id').joins(:user).where('users.id=(?)', user)
will generate
SELECT state_id FROM "centres" INNER JOIN "centres_users" ON "centres_users"."centre_id" = "centres"."id" INNER JOIN "users" ON "users"."id" = "centres_users"."user_id" WHERE (users.id = (5))
Which return 'SA', 'VIC', 'VIC'
but the whole query will generate
SELECT DISTINCT "centres".* FROM "centres" WHERE (centres.state_id IN (NULL,NULL,NULL))
Does user also has state_id column if yes then try this,
User.joins("LEFT OUTER JOIN users ON users.state_id = centers.state_id")
else
try User.joins(:center)
Solved.
.select(:state_id)
will retrieve a model with only the state_id column populated. To retrieve a field, use
.pluck(:state_id)
Below is the final query I had
Centre.where('centres.state_id IN (?)', Centre.joins(:user).where('users.id=(?)', user).pluck('state_id').uniq)