has_many 构建方法，Rails [英] has_many build method, Rails

问题描述

另一个新手问题.

目标:每种成分都可以有零个或多个与之相关的单位转换.我想在显示特定成分的页面上放置一个创建新单位转换的链接.我无法让它正常工作.

The goal: each ingredient can have zero or more unit conversions tied to it. I want to put a link to creating a new unit conversion on the page that shows a specific ingredient. I can't quite get it to work.

成分模型:

class Ingredient < ActiveRecord::Base
   belongs_to :unit
   has_many :unit_conversion
end

单位换算模型:

class UnitConversion < ActiveRecord::Base
  belongs_to :Ingredient
end

单位转换控制器(新)

def new
    @ingredient = Ingredient.all
    @unit_conversion = @ingredient.unit_conversions.build(params[:unit_conversion])
    if @unit_conversion.save then
        redirect_to ingredient_unit_conversion_url(@ingredient, @comment)
        else
            render :action => "new"
        end
  end

相关路线:

  map.resources :ingredients, :has_many => :unit_conversions

显示成分链接:

<%= link_to 'Add Unit Conversion', new_ingredient_unit_conversion_path(@ingredient) %>

这是错误:

 NoMethodError in Unit conversionsController#new

undefined method `unit_conversions' for #<Array:0x3fdf920>

RAILS_ROOT: C:/Users/joan/dh
Application Trace | Framework Trace | Full Trace

C:/Users/joan/dh/app/controllers/unit_conversions_controller.rb:14:in `new'

帮助！我对此很困惑.

推荐答案

new 和 create 的单位转换控制器应该是:

Unit Conversion Controller for new and create should be:

def new
  @ingredient = Ingredient.find(params[:ingredient_id])    
  @unit_conversion = @ingredient.unit_conversions.build
end

def create
  @ingredient = Ingredient.find(params[:ingredient_id])    
  @unit_conversion = @ingredient.unit_conversions.build(params[:unit_conversion])

  if @unit_conversion.save
    flash[:notice] = "Successfully created unit conversion."
    redirect_to ingredient_unit_conversions_url(@ingredient)
  else
    render :action => 'new'
  end
end

此外，这个截屏视频是嵌套资源的好资源.

Also, this screencast is a nice resource for nested resources.

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