error NoMethodError (undefined method `+' for ActiveRecord::Associations::BelongsToAssociation:0xb6c9b45c)

I'm using Rails 2.3.11. I have 2 tables customers and posts:

# Table name: customers
#  id                 :integer(4)      not null, primary key
#  Name               ::string(255)     default("Anonymous")
...

class Customer < ActiveRecord::Base
  has_many :posts
...

# Table name: posts
#  id                   :integer(4)      not null, primary key
#  customer_id          :integer(4)
...

class Post < ActiveRecord::Base
  belongs_to :customer
...

In my posts_controller, I wanted to return the XML response for a GET call, with corresponding post and customer details.

@customer = Customer Details
@posting = Corresponding Post

Following line throws the error NoMethodError (undefined method '+' for ActiveRecord::Associations::BelongsToAssociation:0xb6c9b45c):

respond_to do |format|
  format.xml  { render :xml => (@customer + @posting)}

This looks to be a very开发者_高级运维 trivial issue and I'm missing some basics here. Can some one help me understand this error.

Sounds like you need this:

format.xml  { render :xml => @posting.to_xml(:include => :customer) }

If you ever want the posts a customer has created you would use:

format.xml  { render :xml => @customer.to_xml(:include => :posts) }

Just an FYI.. I would name the singular instance version of your object the same.. So a Post object would be @post :)