Rails - activerecord model serializer group results by specific column in the foreign table

Question

I want to use the ActiveRecord model serializer to show results from the primary key table and foreign key table. However, I want the results to be presented grouped by a column in the foreign key table.

cats = Cats.paginate(page: params[:page], per_page: 20)
render json: cats, meta: pagination(cats), adapter: :json

In the ActiveRecord model serializer:

class CatSerializer < ActiveModel::Serializer
attributes :cat, :persons

 def persons
   object.person
 end

 def cat
   { id: object.id, cat_name: object.name}
 end

Now cat_name is not unique and Persons can share many cat_names. please note that Person => has_many Cats, but cat_name can be similar to multiple Persons. How can I show the data in this format:

"results": [
{
  "cat": {
    "id": 11,
    "cat_name": "Luzi",
    ...
  },
  "persons": [
    {
      "id": 1,
      "name": "andy"
    },
    {
      "id": 2,
      "name": "david"
    }

Please also note that groyp_by(&:cat_name) does not work with pagination.

Answer 1

You can use custom serializer that accepts an already groupby ActiveRecord result

def index
  @cats = Cat.joins(:persons).group("persons.name")
  render json: @cats, serializer: GroupedCatSerializer
end

And you can define custom serializer like

class GroupedCatSerializer < ActiveModel::Serializer

  # method override
  def serializable_object(options={})
    @object.map do |group_key, models|
      [ group_key , serialized_models(models) ]
    end.to_h
  end

  private

  def serialized_models models
    models.map{ |model| CatSerializer.new(model, root: 
    false) }
  end

end