Question

I’m trying to implement the Railscast 340 that demos how to use DataTables, which looks like an awesome gem for my project.

My model is different, of course; but the datatables class the Mr Bates builds (very quickly), in order to do server-side processing, is rather complicated to follow. I got the source code, and basically attempted to follow along. My view comes up with zero records (but there are > 10,000 records), but does not break.

However, here is what the error message output from the rails server says just before it stops:

NameError (undefined local variable or method `genotypes' for #<GenotypesDatatable:0xa9e852c>):
  app/datatables/genotypes_datatable.rb:12:in `as_json'
  app/controllers/genotypes_controller.rb:8:in `block (2 levels) in index'
  app/controllers/genotypes_controller.rb:6:in `index'

Just before this, there appears to be this JSON error, which starts:

Started GET "/genotypes.json?sEcho=1&iColumns=8&sColumns=&iDisplayStart=0&iDisplayLength=10&mDataProp_0=...

The relevant part of the genotypes controller looks like this:

  def index
     respond_to do |format|
      format.html
      format.json { render json: GenotypesDatatable.new(view_context) }
    end
  end

And my genotypes model looks like:

class Genotype < ActiveRecord::Base
  attr_accessible :allele1, :allele2, :run_date
  belongs_to :gmarkers
  belongs_to :gsamples

end

My datatables class is given below. This is from Mr Bates code, modified (most likely incorrectly) to replace his Products model with my Genotypes model:

class GenotypesDatatable
  delegate :params, :h, :link_to, to: :@view

  def initialize(view)
    @view = view
  end

  def as_json(options = {})
    {
      sEcho: params[:sEcho].to_i,
      iTotalRecords: Genotype.count,
      iTotalDisplayRecords: genotypes.total_entries,
      aaData: data
    }
  end

private

  def data
    genotypes.map do |genotype|
      [
        link_to(genotype.name, genotype),
        h(genotype.category),
        h(genotype.released_on.strftime("%B %e, %Y")),
        genotype.run_date
      ]
    end
  end

  def Genotypes
    @Genotypes ||= fetch_Genotypes
  end

  def fetch_genotypes
    genotypes = Genotype.order("#{sort_column} #{sort_direction}")
    genotypes = genotypes.page(page).per_page(per_page)
    if params[:sSearch].present?
      genotypes = genotypes.where("name like :search or category like :search", search: "%#{params[:sSearch]}%")
    end
    genotypes
  end

  def page
    params[:iDisplayStart].to_i/per_page + 1
  end

  def per_page
    params[:iDisplayLength].to_i > 0 ? params[:iDisplayLength].to_i : 10
  end

  def sort_column
    columns = %w[gmarker gsample allele1 allele2 run_date]
    columns[params[:iSortCol_0].to_i]
  end

  def sort_direction
    params[:sSortDir_0] == "desc" ? "desc" : "asc"
  end
end

Any hints on how to troubleshoot (or fix!) this error much appreciated! (Getting this working for my project would be awesome!)

TIA,
rixter

Answer 1

I’m not sure if this is it, but your class has a Genotype method with capital G, it should be all lowercase.