Count distinct pairs of attributes in Rails

Question

I have a class Restaurant: Restaurant(id: integer, name: string, url: string, address: string

I would like to get all the different combinations of url and name and count them. How can I do that?

I've tried

Restaurant.select(:url, :name).distinct.count

but I get:

No function matches the given name and argument types. You might need to add explicit type casts.

It works with my models. just for curiosity, try `Restaurant.all.select(:url, :name).distinct`. — iGian, Jun 18 '18 at 17:02
Sorry. I forgot to add the `.count` that is what is causing the error. — Leticia Esperon, Jun 18 '18 at 17:09

score 2 · Accepted Answer · edited Jun 18 '18 at 18:46

2

Did you try?

Restaurant.pluck(:url, :name).uniq.count

edited Jun 18 '18 at 18:46

Leticia Esperon

answered Jun 18 '18 at 16:54

Ravi Mariya

For more on counting uniq field https://stackoverflow.com/questions/36608/how-can-i-count-the-number-of-records-that-have-a-unique-value-in-a-particular-f – Ravi Mariya Jun 18 '18 at 18:50
4

Wrong answer, the above will FIRST query all records into memory, THEN count the unique combination inside Ruby, not the db. The right way to do this would be: `Restaurant.count("DISTINCT(url, name)")` – Niels Kristian Jun 11 '19 at 13:20

1 Answers1