Question

We have 3 models model1, model2, model3. This 3 are connect with

class Model1 < ActiveRecord::Base
  has_many :model2s
end
class Model2 < ActiveRecord::Base
  belongs_to :model1s
  has_many :model3s
end
class Model3 < ActiveRecord::Base
  belongs_to :model2s
end

In the table of Model1 exists id.

In the table of Model2 exists id and model1_id.

In the table of Model3 exists id and model2_id.

Now i want to get Data from the table1 and table2 out of Model3Controller.
This works fine.

class Model3Controller < ApplicationController
  def create
    @model2controller = Model2.find(params[:model3controller][:model2_id])
    @model1controller = ?
  end
end

How do we get data from the associated dataset from the table1 of the model1controller? Did we have to add the model1_id into the table3, or can we call it on an other way. Like this pseudocode

@model1controller = Model1.find(
params[:model3controller][:model2_id]params[:model2controller][:model1_id])

Answer 1

I might be missing something, but it looks like you should only do the following:

model1 = Model3.find_by_id(params[:model3_id]).model2.model1

Edit. The above code works just like the following lines:

model3 = Model3.find_by_id(params[:model3_id]) # instantiate a model3

model2 = model3.model2 # from mode3 grab a model2
                       # this is possible due to the fact that model3 is associated with model2 via the belongs_to relation

model1 = model2.model1 # model2 "belongs_to" model1, i.e. we can grab model1 by asking model2: "whom do belong to?" just like in the previous example

Please note that accessing methods on instance is done calling in lowercase, i.e.

object.method # => something is returned

In your example you make mistake, calling Model3.find_by_id(params[:id]).Model2 (notice the capital letter in Model2, which is wrong)

Also, check if params[:id] are actually being passed to the controller action. Otherwise, if it’s absent, Model3.find_by_id(params[:id]) will return nil and thus a mentioned error will be raised.