Error while using distinct method rails4

Question

I am using rails4 with mysql database. I want to fetch the unique name and I am using distinct method. Product Template

<%= collection_select(:metal, @product.id, @product.metal_specs.all, :id, :unique_name) %>

MetalSpec model

def unique_name
  self.select(:name).distinct
end

But its giving me an error- private method `select' called for MetalSpec.

Please help me to solve this issue.

Answer 1

You are trying to call select on the model MetalSpec whereas you want to call select on a collection.

Its hard to tell without knowing your schema but maybe you need something like

self.metal_specs.select(:name).distinct

in your product model

Answer 2

 has_many :metal_specs , -> { distinct }, through: :metals

Solved this way. :)

Answer 3

Your code is calling select on an instance.

Also - if you are after just a list of names, I'd suggest you use pluck. As this is returning a list of names, I think the method should be plural

def unique_names
  metal_specs.pluck(:name).uniq
end