Retrieving data in a hash - ruby-on-rails

Question

I need to get some data from ActiveRecord, I have following two tables Department and users I have issue that I am getting one hash in which user is giving me user_ids and emails, now I want to create hash container users, departments and emails in specific format. I have tried a lot map/select but still could not figure out any simple way.
class User < ApplicationRecord
belongs_to :department
end
And Department
class Department < ApplicationRecord
has_many :users
end
I am getting following values from user
sample_params = [{ user_id: 1, email: 'example1#example.com' },
{ user_id: 5, email: 'example5#example.com' },
{ user_id: 13, email: 'example13#example.com'}]
Now I have retrieve departments from database and other data and join in one huge hash so I can add it to my class. I can get all my users by following command
users = User.where(id: sample_params.map{ |m| m[:user_id] })
I will get whole ActiveRecord objects with all users if I run following command I am getting all user_id and project_id
users.map { |u| {user_id: u.id, department_id: u.department_id } }
I will get this
[{:user_id=>1, :department_id=>3},
{:user_id=>5, :department_id=>3},
{:user_id=>13, :department_id=>2}]
but I want to create following hash, Is there any simple way to do it directly using query or in other few lines, I can try using Iteration but that would be very long and complicated. As I also need to merge emails in it and add one project instead of same projects multiple ids.
[
{department_id: 1, users: [{user_id: 1, email: 'example1#example.com'},
{user_id: 5, email: 'example5#example.com'}]},
{department_id: 2, users: [{ user_id: 13, email: 'example13#example.com']
I am using here sample data the real data is very very large include hundreds of users and many departments.

Answer 1

I don't think you can do it in one go! let us run throgh and try how can we solve it. First instead of using map in your params let us try another alternate for it. Remove following line
users = User.where(id: sample_params.map{ |m| m[:user_id] })
user following line
User.where(id: sample_params.pluck(:user_id)).pluck(:department_id, :id).grou
p_by(&:first)
This will bring you result in each users id with department grouping in one query
{3=>[[3, 1], [3, 5]], 2=>[[2, 13]]}
Now we are getting department_id and user_id so we will run map on them to get first array with department_id and user_id in a group with following command
data =
User
.where(id: sample_params.pluck(:user_id))
.pluck(:department_id, :id)
.group_by(&:first).map do |department_id, users|
{ department_id: department_id,
users: users.map { |_, id| id } }
end
This will give you hash with department and users
[{:department_id=>3, :users=>[1, 5]}, {:department_id=>2, :users=>[13]}]
Now you have hash of department and users. so let us work on this this is second phase where I will use select to get email from your params and merge it to your data.
result = []
data.each do |department|
department_users = []
department[:users].each do |user|
emails = sample_params.select { |user| user[:user_id] == 1 }[0][:email];
department_users << { id: user, emails: emails }
end; result << {department_id: department[:department_id], users: department_users}
end
Now if you do puts result[0] you will get following hash as you wanted.
{:department_id=>3, :users=>[{:id=>1, :emails=>"example1#example.com"}, {:id=>5, :emails=>"example1#example.com"}]}, {:department_id=>2, :users=>[{:id=>13, :emails=>"example1#example.com"}]}
This will solve issue, I understand there are two operation but there is no double sql queries in single it is working and you are also replacing your emails. I hope it solve you issue, any one can make it simpler would be appreciated.