Rails 4 Update Nested Attributes

问题

Updating Nested Attributes append instead of updating in has many relationships I am trying to use Rails 4 Update_attributes

Class Person <ActiveRecord::Base
 has_many :pets
 accepts_nested_attributes_for :pets
end

Class Pet < ActiveRecord::Base
 belongs_to :person
end

In my controller I am recieveing the params as {id: 23, house_no:'22A', pets: [{name:'jeffy', type:'dog'}, {name:'sharky', type:'fish'}]}

and my update method is

def update
  @Person = Person.find(params[:id])
  if @Person.update(person_params)
    @Person.save
    render 'persons/create', status 200
  else
    render 'persons/create', status 400
  end
end

private
def person_params
  person_params = params.permit(:house_no)
  person_params.merge! ({pets_attributes: params[:pets]}) if params[:pets].present?
  person_params
end

Now when I update it and if the person already has a pet then the new pets gets appended instead of getting updated eg if a person with id 1 has 1 pet named "Tiger" and I update that person with 2 pets named "Shasha" and "Monti" then the person record has 3 pets (Tiger, Shasha and Monti) instead of updating it to 2 (Shasha and Monti)

回答1:

see the manual:

http://api.rubyonrails.org/v4.0.1/classes/ActiveRecord/NestedAttributes/ClassMethods.html

you need to send in your attributes like pets_attributes:[{name:'jeffy', type:'dog'}, {name:'sharky', type:'fish'}]

and it should work fine.

Please read

You can now set or update attributes on the associated posts through an attribute hash for a member: include the key :posts_attributes with an array of hashes of post attributes as a value.For each hash that does not have an id key a new record will be instantiated, unless the hash also contains a _destroy key that evaluates to true.

回答2:

Update the Person model as below:

class Person < ActiveRecord::Base  ## NOTE: class (c lowercase) and NOT Class
 has_many :pets
 accepts_nested_attributes_for :pets, allow_destroy: true  ## Added allow_destroy
end

In order to destroy the associated model i.e., Pet through the attributes hash, you have to enable it first using the :allow_destroy option.

Then, from your view, you will need to pass the _destroy attribute for the pets that you would like to be removed.

Since, you haven't shared the view specific code. Following is an example of how it should be implemented in your view. Change it according to your requirement:

<%= form_for @person do |f| %>
  <%## .. %>  
  <%= f.fields_for :pets do |builder| %>
    <%## .. %>    
    <%= builder.check_box :_destroy %>
    <%= builder.label :_destroy, "Remove Pet" %>
  <% end %>
<% end %>

In the above code, you would need to add the checkbox and label for passing _destroy value.

After this, update the person_params method in your controller as below:

def person_params
  params.require(:person).permit(:house_no, pets_attributes: [:id, :name, :type, :person_id, :_destroy])
end 

NOTE:

You should not be defining instance variables with capitalized name. Capitalized names are used for declaring Constants in Ruby.

def update
  @person = Person.find(params[:id])
  if @person.update(person_params)
    @person.save
    render 'persons/create', status 200
  else
    render 'persons/create', status 400
  end
end  

回答3:

Can you try adding the :id attribute to the :pets_attributes array in person_params?

You need to permit the id attribute.

回答4:

Probably 1. you would want to assign pets separately,

@Person.pets = Pets.find(params[:pets])

Or 2. clear the pets before saving Person.

@Person.pets.destroy

回答5:

Try changing your person_params as

def person_params
  person_params = params.require(:person).permit(:house_no ,pets_attributes: [:name,:type])
end

And remove @person.save from the update method.You don't need it.And also use ! for update

def update
  @Person = Person.find(params[:id])
  if @Person.update!(person_params)
    render 'persons/create', status 200
  else
    render 'persons/create', status 400
  end
end

Update

And also,as i can see there is no belongs_to :person association in Pet model,Add it in the model

Class Pet < ActiveRecord::Base

belongs_to :person

end

And now permit the person_id attribute by adding it in the params

def person_params
  person_params = params.require(:person).permit(:house_no,pets_attributes: [:name,:type,:person_id])
end

回答6:

You need to edit you params with pets_attributes

Also need to add :id paramter in the pet objects.

来源：https://stackoverflow.com/questions/23492873/rails-4-update-nested-attributes