I'm trying to figure out how to query this relationship without using find_by_sql
class User < ActiveRecord::Base
has_many :lists
end
class List < ActiveRecord::Base
has_many :list_items
belongs_to :user
end
class ListItem < ActiveRecord::Base
belongs_to :list
belongs_to :item
end
class Item < ActiveRecord::Base
has_many :list_items
end
this should be what we are using but How would I do this not by find_by_sql
in user.rb
def self.find_users_who_like_by_item_id item_id
find_by_sql(["select u.* from users u, lists l, list_items li where l.list_type_id=10 and li.item_id=? and l.user_id=u.id and li.list_id=l.id", item_id])
end
I've tried several different includes / joins / merge scenarios but am not able to get at what I'm trying to do.
thx
It's a bit difficult to tell exactly what query you're trying to do here, but it looks like you want the user records where the user has a list with a particular list_type_id and containing a particular item. That would look approximately like this:
User.joins(:lists => [:list_items]).where('lists.list_type_id = ? and list_items.item_id = ?', list_type_id, item_id)
This causes ActiveRecord to execute a query like the following:
SELECT "users".* FROM "users" INNER JOIN "lists" ON "lists"."user_id" = "users"."id" INNER JOIN "list_items" ON "list_items"."list_id" = "lists"."id" WHERE (lists.list_type_id = 10 and list_items.item_id = 6)
and return the resulting collection of User objects.
Related
i have the models User, Company, Product, View
class Company < ActiveRecord::Base
has_many :users
end
class Product < ActiveRecord::Base
has_many :views_by_user, -> { where viewable_type: User },
as: :viewable, class_name: "View"
end
class User < ActiveRecord::Base
has_many :viewed, as: :viewer, class_name: "View"
belongs_to :company
end
class View < ActiveRecord::Base
belongs_to :viewable, polymorphic: true
belongs_to :viewer, polymorphic: true
end
What i did with the above is, when a user views product, i save the data in the views
Now i want the list of distinct companies that have looked at my product(via user) and total count for my serializer. what i have done is,
distinct_users = #product.views_by_user
.includes(viewer: [:company])
.joins("left outer join users on views.viewer_id = users.id")
.select("distinct users.company_id, views.*")
but with this, i would have to do something like
distinct_users.will_paginate(...).map(&:viewer).map(&:company)
is there a better way to do it? also if i use distinct_users.count it throws me an error
PG::UndefinedFunction: ERROR: function count(integer, views) does not exist
LINE 1: SELECT COUNT(distinct users.company_id,...
Start from Company if this is the type of record you actually want. You can use merge to combine the conditions on a relation with those from another. Try this:
Company.joins(:users => :viewed).merge(View.where(viewable: #product))
HTH
Consider the following:
class User < ActiveRecord::Base
has_many :events
end
class Event < ActiveRecord::Base
belongs_to :user #this user is the event owner
has_many :members
end
class Members < ActiveRecord::Base
belongs_to :user
belongs_to :event
end
Now, I need to list all the members for which current_user is the owner. so I have come up with this:
#members = Member.where event_id: current_user.events
which produces the following query:
SELECT "members".* FROM "members" WHERE "members"."event_id" IN (SELECT "events"."id" FROM "events" WHERE "events"."user_id" = 1)
This works as expected but uses subqueries instead of JOIN. Does anyone know a better way to write this same query?
Add a has_many :through association to your User model:
class User < ActiveRecord::Base
has_many :events
has_many :members, :through => :events
end
Now you can query for all a user's members through the members association:
user.members
The SQL generated will look something like:
SELECT "members".* FROM "members" INNER JOIN "events" ON "members"."id" = "events"."member_id" WHERE "events"."user_id" = 1
Transformed to JOIN syntax (with table aliases to make it shorter and easier to read):
SELECT m.*
FROM events e
JOIN members m ON m.event_id = e.id
WHERE e.user_id = $1
I guess this will work.
Member.joins(:event).where("events.user_id = ?" , current_user.id)
You could do something like :
Member.joins(:event).where(events: {user_id: current_user.id})
I have an application where users can customize a calendar and fill it with a given pool of events. A user can also overwrite a title for his own calendar by an alias. So I have the following has_many :through relation:
class Calendar < ActiveRecord::Base
has_many :event_aliases
has_many :events, :through => :event_aliases
end
class Event < ActiveRecord::Base
attr_accessible :title
has_many :event_aliases
has_many :calendars, :through => :event_aliases
end
class EventAliases < ActiveRecord::Base
attr_accessible :course_id, :calendar_id, :custom_name
belongs_to :event
belongs_to :calendar
end
No I want to deliver the calendar with the aliases. If an event has an alias (custom_name), it should be displayed. Otherwise the default event name (title) should be displayed.
Is there a way to easily set up a query that returns all events for the current calendar whether with a custom_name (if exists) or with the default title?
My current solution is to hardcode an if condition into the query which I would like to avoid.
title_column = "case when custom_name IS NOT NULL then custom_name else title end as title"
# assume we are given a calendar_id
Calendar.find(calendar_id).event_aliases.joins(:event).select(title_column, :event_id).each do |event_alias|
# do further stuff here
end
I also could fetch all event_aliases and run through each of them to get the default title if necessary.
# assume we are given a calendar_id
Calendar.find(calendar_id).event_aliases.each do |event_alias|
title = event_alias.custom_name
if title.nil?
title = Event.find(event_alias.event_id).title
# do further stuff here
end
But this one results in too many queries to me.
So is there any smarter way of accomplishing what I want? Maybe using named scopes or another fancy rails technique?
UPDATE
I ended up with making a "custom" select via the has_many :through relationship. So the only thing changes is the Calendar model:
class Calendar < ActiveRecord::Base
has_many :event_aliases
has_many :events, :through => :event_aliases,
:select => "event_aliases.custom_name as custom_name, events.*"
end
So accessing the custom_name / the title now happens a little like #Doon suggested:
Calendar.find(1).courses.each do |course|
title = course.custom_name || course.title
end
This creates only 2 queries instead of 3:
Calendar Load (0.6ms) SELECT `calendars`.* FROM `calendars` WHERE `calendars`.`id` = 1 LIMIT 1
Event Load (0.7ms) SELECT event_aliases.custom_name as custom_name, events.* FROM `events` INNER JOIN `event_aliases` ON `events`.`id` = `event_aliases`.`event_id` WHERE `event_aliases`.`calendar_id` = 1
what about using includes to grab the events at the same time as you pull the aliases.
Calendar.find(1).event_aliases.includes(:event).each do |e|
puts e.custom_name.blank? ? e.event.title : e.custom_name
end
the SQL Rails generates will look something like this:
Calendar Load (0.2ms) SELECT "calendars".* FROM "calendars" WHERE "calendars"."id" = ? LIMIT 1
EventAlias Load (0.2ms) SELECT "event_aliases".* FROM "event_aliases" WHERE "event_aliases"."calendar_id" = 1
Event Load (0.2ms) SELECT "events".* FROM "events" WHERE "events"."id" IN (1, 2)
also if you want to clean it up a bit you can add a virtual field to the EventAlias
class EventAlias < ActiveRecord::Base
def name
custom_name || self.event.title
end
end
As long as you use the includes, the queries will be be the same.
I have two models
class User < ActiveRecord::Base
has_one :work
end
class Work < ActiveRecord::Base
belongs_to :user
end
I need to have distinct description from Work table for specific country's users
I have written following query
Work.includes(:user).where("users.country_name = ?",'IN').select("distinct works.description").limit(10)
It works but it does not give me distinct works.description
It worked with following query,
Work.includes(:user).where("users.country_name = ?",'IN').group("works.description").limit(10)
I have the following and am trying to figure out how to select the User info (sql at end of question).
# only global_id and list_id
class GlobalList < ActiveRecord::Base
set_table_name :globals_lists
belongs_to :list
end
# user_id
class List < ActiveRecord::Base
has_many :global_lists
belongs_to :user
end
# email
class User < ActiveRecord::Base
has_many :lists
end
How would I select out the emails of the user list assuming I have a global_id (ie assuming a global_id of 256,
select u.* from users u, lists l, globals_lists gl where gl.global_id=256 and gl.list_id=l.id and l.user_id=u.id)
Try this:
User.includes({:lists => :global_lists}).where(['global_lists.global_id = ?', 256])
That will return User objects, which seems to be what you are looking for from your query. You can then get their email from their .email attribute, in a loop, or however you need it.