I want to achieve something that takes exactly 3 seconds on SQL, and I'm struggling with it for hours, I want to load all records and left join if it exists, if not, then don't give me the associated model.
the query I want to create is as follows:
"SELECT * FROM apartments LEFT JOIN comments ON apartments.id = comments.apartment_id AND comments.user_id = ?"
and when I call apartment.comments, it'll give me just the record (can only be one) for the specific user, not all the records for every user.
I tried
Apartment.joins("LEFT OUTER JOIN comments ON comments.apartment_id = apartments.id AND comments.user_id = #{user_id}")
but it doesn't work, as when I call apartments.comments it fires another query which returns all possible comments.
Apartment.includes(:comments).where("comments.user_id = ?", user_id)
doesn't work aswell, because it returns only apartments who has a comment from the specific user.
help is needed!
Maybe you could try this:
#app/models/apartment.rb
Class Apartment < ActiveRecord::Base
has_many :comments
scope :user, ->(id) { where("comments.user_id = ?", id }
end
#apartment = Apartment.find(params[:id])
#comments = #apartment.comments.user(user_id)
Related
I need to create a live chat app and now I have three models :
ChatRoom
ChatRoomMember
ChatRoomMessage
From this three models, I use includes and references to get the list of chat_rooms for current login user. Here is the code that I have wrote.
#chat_rooms = ChatRoom.includes(:members).references(:members)
#chat_rooms = #chat_rooms.includes(:messages).references(:messages)
#chat_rooms = #chat_rooms.where 'chat_room_members.user_id = ?', #current_user.id
#chat_rooms = #chat_rooms.order 'chat_room_messages.created_at DESC'
#chat_rooms = #chat_rooms.limit(limit).offset(offset)
However, the order didn't work as I expected. What I want is that the chat_rooms are sorted by created_at column from the last message in that room. How can I do this ?
Here is the database structure :
Use association to avoid where 'chat_room_members.user_id = ?', #current_user.id
Here is my suggestion, assuming User has associations looking like:
class User
has_many :chat_room_members
has_many :chat_rooms, through: :chat_room_members
end
# list only rooms with at least on message
#chat_rooms = #current_user.chat_rooms.joins(:messages).order('chat_room_messages.created_at DESC').limit(limit).offset(offset)
# list all rooms even if there is no message attached
#chat_rooms = #current_user.chat_rooms.distinct.left_joins(:messages).order('chat_room_messages.created_at DESC').limit(limit).offset(offset)
Try this:
ChatRoom.includes(:messages).order('chat_room_messages.created_at DESC')
Thanks for everyone has help me to solve this probel. I have my own answer. Here is it.
SELECT chat_rooms.*, (SELECT chat_room_messages.created_at FROM chat_room_messages WHERE chat_room_messages.chat_room_id = chat_rooms.id ORDER BY chat_room_messages.id DESC LIMIT 1) AS last_message_at FROM chat_rooms INNER JOIN chat_room_members ON chat_room_members.chat_room_id = chat_rooms.id WHERE chat_room_members.user_id = #{#current_user.id} ORDER BY last_message_at DESC
I use raw query for solve this problem. Hope this can help anyone who need it !
how to get only records that isn't associated in Ebook model? Simply, i want to offer only ebooks that user didnt already have. I tried much solutions, one of best is:
Magazine.left_joins(:ebooks).where(ebooks: { id: nil })
but i dont know where to specify user_id
model Magazine
has_many :ebooks
has_many :users, :through => :ebook
model Ebook
belongs_to :user
belongs_to :magazine
model User
has_many :ebooks
Im new in rails, sorry for stupid question maybe.
#Hass
thank you, but this generate sql like this:
SELECT "magazines".* FROM "magazines"
INNER JOIN "ebooks" ON "magazines"."id" = "ebooks"."magazine_id"
LEFT OUTER JOIN "ebooks" "ebooks_magazines" ON "ebooks_magazines"."magazine_id" = "magazines"."id"
WHERE "ebooks"."user_id" = 1 AND "ebooks"."id" IS NULL
(WHERE "ebooks"."user_id" = 1 => this returns 0 records, because where filter doesnt find any row in table ebooks)
but i need something like this:
SELECT "magazines".*, ebooks.user_id FROM "magazines"
LEFT JOIN "ebooks" ON "magazines"."id" = "ebooks"."magazine_id" AND ebooks.user_id = 1
LEFT OUTER JOIN "ebooks" "ebooks_magazines" ON "ebooks_magazines"."magazine_id" = "magazines"."id"
WHERE ebooks.user_id IS NULL
this returns rows that im looking for but i dont know how to do this with rais and associations
You want to use a left_outer_join instead.
Magazine.left_outer_joins(:ebooks).where(ebooks: { id: nil })
In my rails application, at some point, I query my model simply. I want to query customers order information like how many orders were given by this customer within three months.
Just now, I query the model in that way:
#customer = Customer.all
customer.rb
class Customer < ApplicationRecord
audited
has_many :orders
end
And customer may have orders.
order.rb
class Order < ApplicationRecord
audited
belongs_to :customer
end
What I would like to do is to query customers model and to inject aggregate function result to every customer records.
EDİT
I tried to simulate every solution but couln't achieve.
I have the following query in mysql.
How do I need to code in ruby with activerecord to create that query ?
SELECT
(SELECT
COUNT(*)
FROM
orders o
WHERE
o.customer_id = c.id
AND startTime BETWEEN '2017.12.04' AND '2018.01.04') AS count_last_month,
(SELECT
COUNT(*)
FROM
orders o
WHERE
o.customer_id = c.id
AND startTime BETWEEN '2017.10.04' AND '2018.01.04') AS count_last_three_month,
c.*
FROM
customers c;
How can I achieve that?
Thanks.
Customer.
joins(:orders).
group('customers.id').
where('orders.created_at > DATE_SUB(NOW(), INTERVAL 3 MONTH)')
select('sum(orders.id), customers.*')
As my understanding of you question. I have this solution for you question. Please have a look and try it once. In below query, 'includes' used to solve N+1 problem.
Customer.includes(:orders).where('created_at BETWEEN ? AND ?', Time.now.beginning_of_day, Time.now.beginning_of_day-3.months).group_by{|c|c.orders.count}
If you are looking for particular customer's order count then you can try this one.
#customer.orders.where('created_at BETWEEN ? AND ?', Time.now.beginning_of_day, Time.now.beginning_of_day-3.months).group_by{|c|c.orders.count}
How do I get all the users who do not have a car?
class User < ActiveRecord::Base
has_one :car
end
class Car < ActiveRecord::Base
belongs_to :user
end
I was doing the following:
all.select {|user| not user.car }
That worked perfect until my database of users and cars got too big and now I get strange errors, especially when I try and sort the result. I need to do the filtering in the query and the ordering as well as part of the query.
UPDATE: What I did was the following:
where('id not in (?)', Car.pluck(:user_id)).order('first_name, last_name, middle_name')
It's fairly slow as Rails has to grab all the user_ids from the cars table and then issue a giant query. I know I can do a sub-query in SQL, but there must be a better Rails/ActiveRecord way.
UPDATE 2: I now have a noticeably more efficient query:
includes(:car).where(cars: {id: nil})
The answer I accepted below has joins with a SQL string instead of includes. I don't know if includes is more inefficient because it stores the nil data in Ruby objects whereas joins might not? I like not using strings...
One way is to use a left join from the users table to the cars table and only take user entries that don't have any corresponding values in the cars table, this looks like:
User.select('users.*').joins('LEFT JOIN cars ON users.id = cars.user_id').where('cars.id IS NULL')
Most of the work that needs to be done here is SQL. Try this:
User.joins("LEFT OUTER JOIN cars ON users.id = cars.user_id").where("cars.id IS NULL")
It is incredibly inefficient to do this with ruby, as you appear to be trying to do.
You can throw an order on there too:
User.
joins("LEFT OUTER JOIN cars ON users.id = cars.user_id").
where("cars.id IS NULL").
order(:first_name, :last_name, :middle_name)
You can make this a scope on your User model so you only have one place to deal with it:
class User < ActiveRecord::Base
has_one :car
def self.without_cars
joins("LEFT OUTER JOIN cars ON users.id = cars.user_id").
where("cars.id IS NULL").
order(:first_name, :last_name, :middle_name)
end
end
This way you can do:
User.without_cars
In your controller or another method, or even chain the scope:
User.without_cars.where("users.birthday > ?", 18.years.ago)
to find users without cars that are under 18 years old (arbitrary example, but you get the idea). My point is, this kind of thing should always be made into a scope, so it can be chained with other scopes :) Arel is awesome that way.
I have User and Album models with HABTM relationship
class Album < ActiveRecord::Base
has_and_belongs_to_many :users
class User < ActiveRecord::Base
has_and_belongs_to_many(:albums)
I'd like to find all the albums that are stored in the database but not associated with a particular user.
So far my code is like this:
Album.all(:order => "albums.created_at DESC", :include => "users", :limit => limit, :conditions => ["users.id != ? AND users.id IS NOT NULL", current_user.id])
but for some reason this is not working. It's returning albums that are associated with current_user.
here take a look at this ouptput from the console.
Check the users id i first fetch.
Then i fetch albums which should not have the users id
I then find one of the listed albums and ask it to return the associated users
one of those associated users is the one from above and shouldnt be there.
Can anyone help with the above?
I usually try to stay away sub-selects but I can't seem to get it to work any other way:
class Album < ActiveRecord::Base
scope :without_user, lambda{|u| where("#{quoted_table_name}.id NOT IN (SELECT `albums_users`.album_id FROM `albums_users` WHERE `albums_users`.user_id = ?)", u.id) }
end
user = User.find(30)
Album.without_user(user)
Assuming you created table albums_users to hold relationship data:
Album.includes(:users).
where(["albums_users.user_id IS NULL OR albums_users.user_id != ?", user_id])
I think it will generate SQL along the lines of
SELECT *
FROM albums LEFT OUTER JOIN albums_users ON albums.id = albums_users.album_id
WHERE albums_users.album_id IS NULL OR albums_users.album_id != #{user_id}
Try:
:conditions => ["users.id <> ? AND users.id IS NOT NULL", current_user.id]
A non-sql solution would be:
Album.all.reject{|album| user.albums.include?(album)}
Obviously, if you have tens of thousands of rows in your database, you might not want to do this.
Might do something like this, too:
Album.where(["id NOT IN (?)", user.albums_ids])
But if your users have a lot (say hundreds) of albums, you shouldn't do this either.
Just throwing in easy solutions if you're out for one of those.