问题
I have a form that lets me create new blog posts and I'd like to be able to create new categories from the same form.
I have a habtm relationship between posts and categories, which is why I'm having trouble with this.
I have the following 2 models:
class Post < ActiveRecord::Base
has_and_belongs_to_many :categories
attr_accessible :title, :body, :category_ids
accepts_nested_attributes_for :categories # should this be singular?
end
class Category < ActiveRecord::Base
has_and_belongs_to_many :posts
attr_accessible :name
end
My form lets me pick from a bunch of existing categories or create a brand new one. My form is as follows.
# using simple_form gem
.inputs
= f.input :title
= f.input :body
# the line below lets me choose from existing categories
= f.association :categories, :label => 'Filed Under'
# I was hoping that the code below would let me create new categories
= f.fields_for :category do |builder|
= builder.label :content, "Name"
= builder.text_field :content
When I submit my form, it gets processed but the new category is not created. My command prompt output tells me:
WARNING: Can't mass-assign protected attributes: category
But, if I add attr_accessible :category, I get a big fat crash with error message "unknown attribute: category".
If I change the fields_for target to :categories (instead of category) then my form doesn't even display.
I've spent a while trying to figure this out, and watched the recent railscasts on nested_models and simple_form but couldn't get my problem fixed.
Would this be easier if I was using a has_many :through relationship (with a join model) instead of a habtm?
回答1:
Thanks to everyone who answered. After much trial and error, I managed to come up with a fix.
First of all, I switched from a HABTM to a has_many :through relationship, calling my join model categorization.rb (instead of categorizations_posts.rb) - NB: the fix detailed below will likely work with a HABTM too:
Step 1: I changed my models to look like this:
# post.rb
class Post < ActiveRecord::Base
has_many :categorizations
has_many :categories, :through => :categorizations
attr_accessible :title, :body, :category_ids
accepts_nested_attributes_for :categories
end
#category.rb
class Category < ActiveRecord::Base
has_many :categorizations
has_many :posts, :through => :categorizations
attr_accessible :name, :post_ids
end
#categorization.rb
class Categorization < ActiveRecord::Base
belongs_to :post
belongs_to :category
end
From the post model above: obviously, the accessor named :category_ids must be present if you want to enable selecting multiple existing categories, but you do not need an accessor method for creating new categories... I didn't know that.
Step 2: I changed my view to look like this:
-# just showing the relevent parts
= fields_for :category do |builder|
= builder.label :name, "Name"
= builder.text_field :name
From the view code above, it's important to note the use of fields_for :category as opposed to the somewhat unintuitive fields_for :categories_attributes
Step 3 Finally, I added some code to my controller:
# POST /posts
# POST /posts.xml
def create
@post = Post.new(params[:post])
@category = @post.categories.build(params[:category]) unless params[:category][:name].blank?
# stuff removed
end
def update
@post = Post.find(params[:id])
@category = @post.categories.build(params[:category]) unless params[:category][:name].blank?
# stuff removed
end
Now, when I create a new post, I can simultaneously choose multiple existing categories from the select menu and create a brand new category at the same time - it's not a case of one-or-the-other
There is one tiny bug which only occurs when editing and updating existing posts; in this case it won't let me simultaneously create a new category and select multiple existing categories - if I try to do both at the same time, then only the existing categories are associated with the post, and the brand-new one is rejected (with no error message). But I can get round this by editing the post twice, once to create the new category (which automagically associates it with the post) and then a second time to select some additional existing categories from the menu - like I said this is not a big deal because it all works really well otherwise and my users can adapt to these limits
Anyway, I hope this helps someone.
Amen.
回答2:
In your form you probably should render the fields_for once per category (you can have multiple categories per post, hence the habtm relation). Try something like:
- for category in @post.categories
= fields_for "post[categories_attributes][#{category.new_record? ? category.object_id : category.id}]", category do |builder|
= builder.hidden_field :id unless category.new_record?
= builder.label :content, "Name"
= builder.text_field :content
回答3:
I have made my application and my nested form works with HABTM. My model is :
class UserProfile < ActiveRecord::Base
attr_accessible :name, :profession
has_and_belongs_to_many :cities
belongs_to :user
attr_accessible :city_ids, :cities
def self.check_city(user,city)
user.cities.find_by_id(city.id).present?
end
end
class City < ActiveRecord::Base
attr_accessible :city_name
has_and_belongs_to_many :user_profiles
end
In my form I have:
-# just showing the relevent parts
= f.fields_for :cities do|city|
= city.text_field :city_name
And at my controller:
def create
params[:user_profile][:city_ids] ||= []
if params[:user_profile][:cities][:city_name].present?
@city= City.create(:city_name=>params[:user_profile][:cities][:city_name])
@city.save
params[:user_profile][:city_ids] << @city.id
end
@user=current_user
params[:user_profile].delete(:cities)
@user_profile = @user.build_user_profile(params[:user_profile])
respond_to do |format|
if @user_profile.save
format.html { redirect_to @user_profile, notice: 'User profile was successfully created.' }
format.json { render json: @user_profile, status: :created, location: @user_profile }
else
format.html { render action: "new" }
format.json { render json: @user_profile.errors, status: :unprocessable_entity }
end
end
end
def update
params[:user_profile][:city_ids] ||= []
if params[:user_profile][:cities][:city_name].present?
@city= City.create(:city_name=>params[:user_profile][:cities][:city_name])
@city.save
params[:user_profile][:city_ids] << @city.id
end
@user=current_user
params[:user_profile].delete(:cities)
@user_profile = @user.user_profile
respond_to do |format|
if @user_profile.update_attributes(params[:user_profile])
format.html { redirect_to @user_profile, notice: 'User profile was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: "edit" }
format.json { render json: @user_profile.errors, status: :unprocessable_entity }
end
end
end
This code works.
回答4:
Maybe you should try it with (not testet):
attr_accessible :category_attributes
And HBTM relations arent really recommened... But I use them on my own :P
来源：https://stackoverflow.com/questions/3995576/habtm-relationships-and-accepts-nested-attributes-for