Rails - Submitting Nested Values That Already Exist - ruby-on-rails

Question

I have a model, Tran that has a foreign key to the User model. In the view for creation a Tran (transaction), I have a dropdown that allows the user to select the User that started the transaction. When I post this transaction, the record is set with the correct user ID:
Then, in my Trans model I added "belongs_to", as I understand I should do this for foreign keys:
class Tran < ActiveRecord::Base
belongs_to :buying_user, :class_name => 'User'
Now, when my client passes up the params in the post, my Tran.new craps out because I am passing up a userID and not a full record. Is the
#trans_controller.rb
def create
#title = "Create Transaction"
#bombs on this call
#tran = Tran.new(params[:tran])
How am I supposed to handle this?
Update as requested:
tran.rb
class Tran < ActiveRecord::Base
has_many :transaction_users, :dependent => :destroy, :class_name => 'TransactionUser'
belongs_to :submitting_user, :class_name => 'User'
belongs_to :buying_user, :class_name => 'User'
accepts_nested_attributes_for :transaction_users, :reject_if => lambda { |a| a[:content].blank? }, :allow_destroy => true
validates :description, :presence => true,
:length => {:maximum => 100 }
validates :total, :presence => true
validates_numericality_of :total, :greater_than => 0
validates :submitting_user, :presence => true
validates :buying_user, :presence => true
validates_associated :transaction_users
end
user.rb
class User < ActiveRecord::Base
has_many :trans
attr_accessor :password
attr_accessible :firstname, :lastname, :email, :password, :password_confirmation
email_regex = /\A[\w+\-.]+#[a-z\d\-.]+\.[a-z]+\z/i
validates :firstname, :presence => true,
:length => {:maximum => 50 }
validates :lastname, :presence => true,
:length => {:maximum => 50 }
validates :email, :presence => true,
:format => {:with => email_regex },
:uniqueness => { :case_sensitive => false }
validates :password, :presence => true,
:confirmation => true,
:length => { :within => 6..40 }
# Register callback to before save so that we can call extra code like password encryption
before_save :encrypt_password
# Class methods
def self.authenticate(email, submitted_password)
user = find_by_email(email)
return nil if user.nil?
return user if user.has_password?(submitted_password)
end
def self.authenticate_with_salt(id, cookie_salt)
user = find_by_id(id)
(user && user.salt == cookie_salt) ? user : nil
end
# Public methods
def has_password?(submitted_password)
self.encrypted_password == encrypt(submitted_password)
end
def full_name
"#{self.lastname}, #{self.firstname}"
end
def self.active_users
# TODO
#User.find_
User.all
end
private
def encrypt_password
self.salt = make_salt if new_record?
self.encrypted_password = encrypt(password)
end
def encrypt (string)
secure_hash("#{salt}--#{string}")
end
def make_salt
secure_hash("#{Time.now.utc}--#{password}")
end
def secure_hash(string)
Digest::SHA2.hexdigest(string)
end
end
params hash on submit:
{"commit"=>"Submit",
"tran"=>{"total"=>"100",
"submitting_user"=>"1",
"description"=>"Description"},
"authenticity_token"=>"88qI+iqF92fo/M9rPfMs1CLpEXqFLGQXfj0c9krXXac=",
"utf8"=>"✓",
"user"=>"1"}
error:
User(#70040336455300) expected, got String(#70040382612480)
beginning of controller:
def create
#title = "Create Transaction"
#tran = Tran.new(params[:tran])
It crashes on the Tran.new line. Thanks so much!

Answer 1

Typically the User model would have has_many :transactions, :class_name => Tran
Then you would do this...
#user.transaction_create(params[:tran])
or
#user.build
it depends on what parameters are actually passed in params[:tran], but the idea is that the has_many side does the creating of the belongs_to.

Answer 2

I figured it out! The problem the whole time was that my db column name on my Trans table that linked to my Users table was submitting_user instead of submitting_user_id. Then, when I added the belongs_to association to submitting_user rails got confused and made that field a User, instead of an integer.