Is it possible to update following data in one single query?
ID Seq
2 2
1 4
4 1
3 3
It would be best if it could be done with rails active records, else with sql query would be perfectly fine too.
Reason for doing so is I have scenario where I need to update a group of ids frequently based on ajax request. I believe having it done in single query is much more optimized.
I guess you're asking whether you can complete set of updates in a single transaction.
In rails, you can use ActiveRecord::Base.transaction for this purpose. For example, for a Model, you can:
Model.transaction do
Model.update(2, {:seq => 2} )
Model.update(1, {:seq => 4} )
Model.update(4, {:seq => 1} )
Model.update(3, {:seq => 3} )
end
We can not directly call multiple updates in a single query using Active Record. As you said we can run it as a sql query in rails.
sql = ActiveRecord::Base.connection();
sql.execute("INSERT into products (id,name,description) VALUES (id-1,'name4','desc4'),(id-2,'name5','desc5'),(id-3,'name6','desc7') ON DUPLICATE KEY UPDATE name=VALUES(name),description=VALUES(description);")
Found the solution I want from here and here.
This is how I do it with active records.
_params = ["12", "9", "13", "14", "15", "16"]
db = ActiveRecord::Base.connection();
query = "UPDATE #{self.table_name} SET display_order = CASE id "
_params.each_with_index do |d,i|
query += sanitize_sql(["WHEN ? THEN ? ",d,i])
end
query += "END "
query += "WHERE id in ('#{_params.join("','")}') "
Related
I am currently trying to filter out from selected data in Ruby on Rails those where the attribute "amount_available" is greater than zero. This would be no problem via #events.where(ticket_categories.amount_available > 0), but ticket_categories is an array with not a fixed length, because there can be multiple categories. How can you easily iterate through the array in the where clause and do this comparison?
I only need the events in the output where at least one associated category has the amount_available > 0.
This is my code:
#upcoming_events = #events.where("date >=?", Date.current)
#available_events = #upcoming_events.where(ticket_categories[0].amount_available > 0)
json_response(#available_events)
You can chain where conditions and you can add conditions that are based on associated models with joins:
available_events = #events
.where('date >= ?', Date.current)
.joins(:ticket_categories).where('ticket_categories.amount > 0')
.group(:id)
render json: available_events
Note: Database joins might return duplicate records (depending on your database structure and the condition) therefore the need to group the result set by id.
It is only a representation because the Events table is linked to TicketCategories via has_many. I use PostgresSQL and could now solve it with the following code:
#upcoming_events = #close_events.where("date >=?", Date.current)
available_events = []
#upcoming_events.each do |event|
event.ticket_categories.each do|category|
if category.amount_available > 0
available_events.push(event)
break;
end
end
end
render json: available_events
I would like to build a 'waiting_on' list where the users in the list meet two conditions: they do not belong to the current auction (User.where.not(auction: #auction)) and they do belong to the current_game (User.where(game: current_game).
How can I populate the array #waiting_on with users who meet both these requirements in ActiveRecord?
Here's my pseudocode attempt:
#waiting_on = User.where not(auction: #auction) and game: current_game
Update:
At the moment I have got it working like this, but it is a little ugly:
users_in_auction = User.where(auction: #auction)
users_in_game = User.where(game: current_game)
#waiting_on = users_in_game - users_in_auction
I have been trying this: User.where(game: current_game).where.not(auction: #auction), however the fact that the user that is not part of the auction has a nil value for auction_id seems to be messing it up. The SQL query output seemed to be exactly what I needed: SELECT "users".* FROM "users" WHERE "users"."game_id" = 3 AND ("users"."auction_id" != 2)
You can do it in one query by adding a null check:
User.where.not(auction: auction).or(User.where(auction: nil)).where(game: game)
This produces this SQL, which I think is what you want if I'm reading the question right:
SELECT "users".* FROM "users"
WHERE (("users"."auction_id" != 7) OR "users"."auction_id" IS NULL)
AND "users"."game_id" = 5
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)
I have a User that has_many messages.
I need a create a query that will
'Get me all users who's (message.opened == false) count < 3'
Right now, I am using User.all, iterating through all users, and counting manually. I understand that this isn't very efficient and it can be all done in one query, but I am new to SQL/ActiveRecord so need some help here.
Thanks
Assuming Rails 3 syntax. You can do something like:
User.joins(:messages).where(:messages => {:opened => false}).group(:user_id).having("COUNT(messages.id) < 3)
This should work:
User.includes(:messages).group("users.id").where("messages.opened = 0").having("count(messages.id) < 3")
This will create two queries, one for the grouped query, and one for eager loading the resulting users and messages with a join.
Here is solution to your problem
User.includes(:messages).group("users.id").where("messages.opened = 0").having("count(messages.id) < 3")
but what else you can do is to create a scope for this
scope :not_opened_less_three_count, includes(:messages).group("users.id").where("messages.opened = 0").having("count(messages.id) < 3")
And then you can use it anywhere you needed as follow
User.not_opened_less_three_count
Try this
User.includes(:messages).group('users.id').having('SUM(IFNULL(messages.opened = 0, 1)) < 3')
It works at least on MySQL, AND assuming your boolean true are 1 in database.
EDIT I had reversed the condition
PS IFNULL is there to handle if messages.opened can be NULL
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.