#Here goes the description of what happens, below is the related code

#I edit User (with habtm on Program) and validates_presence_of :programs but, even when the validation is triggered, the join table
#gets inconsistent:

-> Original table:


mysql> select user_id,program_id,logname,p.name from programs_users pu,users u, programs p where user_id = u.id and program_id = p.id;
+---------+------------+----------+------+
| user_id | program_id | logname  | name |
+---------+------------+----------+------+
|       2 |          2 | iherrera | SIT  |
+---------+------------+----------+------+
1 row in set (0.00 sec)

-> Create a new user

mysql> select user_id,program_id,logname,p.name from programs_users pu,users u, programs p where user_id = u.id and program_id = p.id;
+---------+------------+----------+------+
| user_id | program_id | logname  | name |
+---------+------------+----------+------+
|       2 |          2 | iherrera | SIT  |
|       3 |          1 | Bar      | SAT  |
+---------+------------+----------+------+

-> Edit the user and remove all programs, I get validation error but the table gets hit anyway!!

1 error prohibited this user from being saved

There were problems with the following fields:

    * Programs cant be blank

but

mysql> select user_id,program_id,logname,p.name from programs_users pu,users u, programs p where user_id = u.id and program_id = p.id;
+---------+------------+----------+------+
| user_id | program_id | logname  | name |
+---------+------------+----------+------+
|       2 |          2 | iherrera | SIT  |
+---------+------------+----------+------+
1 row in set (0.01 sec)


#Models related in habtm

#$ more app/models/user.rb
class User < ActiveRecord::Base
  has_and_belongs_to_many :programs

  validates_presence_of :programs
end

#$ more app/models/program.rb
class Program < ActiveRecord::Base
        belongs_to :project
  has_and_belongs_to_many :users

  validates_presence_of :name, :project_id
  validates_presence_of :project, :message => "does not exist"
end

#Controller
  # POST /users
  # POST /users.xml
  def create

    prog_ids = params[:user][:programs]
    params[:user].delete(:programs)
    @user = User.new(params[:user])
    @user.programs = []
    if prog_ids != nil then
      prog_ids.each do |pi|
        @user.programs << Program.find(pi)
      end
    end

    respond_to do |format|
      if @user.save
        flash[:notice] = 'User was successfully created.'
        format.html { redirect_to(@user) }
        format.xml  { render :xml => @user, :status => :created, :location => @user }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @user.errors, :status => :unprocessable_entity }
      end
    end
  end
  # PUT /users/1
  # PUT /users/1.xml
  def update
    @user = User.find(params[:id])
    prog_ids = params[:user][:programs]
    params[:user].delete(:programs)
    @user.programs = []
    if prog_ids != nil then
      prog_ids.each do |pi|
        @user.programs << Program.find(pi)
      end
    end
    respond_to do |format|
      if @user.update_attributes(params[:user])
        flash[:notice] = 'User was successfully updated.'
        format.html { redirect_to(@user) }
        format.xml  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @user.errors, :status => :unprocessable_entity }
      end
    end
  end