Is it possible to merge two association tables in Sunspot solr

I have four tables. They are Brands, departments, categories and product_details. The models are

Brand model

class Brand < ActiveRecord::Base
  has_many :product_details, :dependent=>:destroy
  searchable do
    integer :id
    text :name
  end
end

Deparment model

class Department < ActiveRecord::Base
  has_many :product_details, :dependent=>:destroy
  searchable do
    integer :id
    text :name
  end  
end

Category model

class Category < ActiveRecord::Base
  has_many :product_details, :dependent=>:destroy
  searchable do
    integer :id
    text :name   
  end
end

ProductDetail model

class ProductDetail < ActiveRecord::Base
  belongs_to :department
  belongs_to :category
  belongs_to :brand
  searchable do
    text :name
    text :brand do
      brand.name
    end
    integer :department_id
    integer :category_id
end

If user searches for department 1 first I have get all product details based on department id. The resultant table must contain brand name, category name and department name also. Is it possible to do it using sunspot solr? How?

I think you should create a Document for each Product with Brand, Department, Category and Product details.
Then you're able to search for what you want, and receive the information you need.