How to get details of grouped object - ruby-on-rails

Question

I am building a Rails 5 app and in this app I got four models.
User, Report, Trip and Expense.
User has_many Reports, trips and expenses
Reports has_many trips and expenses.
I want to get a JSON response with all the trips and expenses that a user has done this month, grouped by Report.
I can do this but I need only the Id and Title of the report (when grouping) and now I get only the object name.
I use this method (located in the User model):
def grouped_reports
trips = self.trips
expenses = self.expenses
items = trips + expenses
items.group_by(&:report)
end
The output in JSON is this:
{
"#<Report:0x007fa225163ba8>": [{
"id": 12,
"account_id": 20,
"user_id": 92,
"vehicle_id": null,
"ttype": null,
"description": "saf",
"start_latitude": 57.4874919,
"start_longitude": 12.0761927999999,
"end_latitude": 59.3293235,
"end_longitude": 18.0685808000001,
"start_address": "Chicago",
"end_address": "New york",
"distance": 490,
"time": null,
"status": "pending",
"registered_at": "2018-08-24T02:00:00.000+02:00",
"approvals_count": 0,
"rejections_count": 0,
"created_at": "2018-08-24T22:39:22.637+02:00",
"updated_at": "2018-08-24T22:39:22.637+02:00",
"report_id": 79,
"return_trip": null,
"triptype_id": 10
},
{
"id": 13,
"account_id": 20,
"user_id": 92,
"cost": 100,
"etype": null,
"description": "sdsd",
"start_address": null,
"end_address": null,
"distance": null,
"reimbursable": false,
"status": "pending",
"registered_at": "2018-08-08T00:00:00.000+02:00",
"created_at": "2018-08-24T22:39:40.343+02:00",
"updated_at": "2018-08-24T22:39:40.343+02:00",
"approvals_count": 0,
"rejections_count": 0,
"report_id": 79,
"expensetype_id": 15
}
]
}
There is two things I need to improve.
Display id and title of report not .
Get only this months reports.
Update, this works but is it the right way in terms of performance?
And not only performance, is it actually using the title of the report as a grouping factor? Which is not good since may reports can share the same title. I want to group by report_id but display report title.
def grouped_reports
trips = self.trips
expenses = self.expenses
items = trips + expenses
items.group_by{ |t| [t.report.id, t.report.title] }
end

Answer 1

Code would differ depending on what JSON format you want to output.
I usually use json generator such jbuilder, but this time I suggest a array and hash structure.
class User < ApplicationRecord
has_many :reports
has_many :expenses
has_many :trips
def grouped_reports
start_date = Time.current.beginning_of_month
monthly_trips = trips.where('created_at >= ?', start_date)
monthly_expenses = expenses.where('created_at >= ?', start_date)
report_ids = (monthly_trips.map(&:report_id) + monthly_expenses.map(&:report_id)).uniq
reports = Report.where(id: report_ids)
reports.map do |report|
{
id: report.id,
title: report.title,
trips: trips.select {|t| t.report_id == report.id},
expenses: expenses.select {|e| e.report_id == report.id}
}
end
end
end
You are grouping with trips and expenses joined to one array, but it is not preferable to put different types in same arrays for JSON. It would be safe to have a hash format and separate key for trip and expense.
To extract records for this month, use where to filter.
It is possible to fetch trips by using includes for reports and expenses, but from a performance point of view it is better to get the related trips at once.
If you want to further improve performance, narrow down only columns used when outputting JSON by using select method. This would be a huge improvement if a lot of records are outputted.