Rails - Apr 2005 - Uploading a File and an Easy "link_to" Question, Please Help

My problem comes with uploading a picture on my website.

Right now I would like to have a form where a user can upload a picture 
and the server will move that picture to public/images. After the 
picture is moved I would like to store the path to this file in my MySQL 
server - so potentially I could just call something like: <img
src="<%=
@post.file %>" in one of my views. If possible, I would also like to 
validate that the uploaded file is an actual JPEG/JPG file under 5 
megabytes.

I have included any information that could potentially be helpful.

Absolute path of public/images:

/mnt/lshare/www/ruby/photoblog/app/public/images

app/controllers/post_controller.rb:

class PostController < ApplicationController
    before_filter :login_required, :except => [:index]
   
    def new
        @post = Post.new
    end

    def create
        @post = Post.new(@params["post"])
        if @post.save
            redirect_to :action => "show", :id => @post.id.to_s
        else
            render_action ''new''
        end
    end
   
    def show
        @post = Post.find(@params["id"])
    end

end

views/post/new.rhtml:

<form action="/post/create" method="post"
enctype="multipart/form-data">
    <p><label for="title">Title:</label><br />
    <%= text_field "post", "title" %></p>
    <p><label
for="description">Description:</label><br />
    <%= text_field "post", "description" %></p>
    <p><label for="file">File:</label><br />
    <% file_field "post", "file" %><input
id="post_file"
name="post[file]" type="file"></p>
    <p><input type="submit" value="Post
It."></p>
<%= end_form_tag %>

photoblog.sql:

CREATE TABLE posts (
 id int(6) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
 title text NOT NULL,
 description text,
 created_on timestamp NOT NULL,
 updated_on timestamp NOT NULL,
 file text NOT NULL
);

CREATE TABLE users (
 id int(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
 login varchar(80) default NULL,
 password varchar(40) default NULL
);


And just one more actually easy question!
When I show the picture, I would like a link to the previous picture. I 
have tried to doing this by putting the id as (@params["id"] - 1) but 
that doesn''t work. It might be a syntax error or something.

views/post/show.rhtml:

<p>The title is: <%= @post.title %></p>
<p>The description is: <%= @post.description %></p>
<p>The post was made on: <%= @post.created_on.strftime "%e %B %Y |
%I:%M
%p" %></p>
<p>The file is:<%= @post.file %>
<br />
<br />
<p><%= link_to "Previous post.", :action =>
"show", id => (@params["id"]
- 1) %>

If you get sick of looking at all this e-mailed code the actual project 
can be found:
http://swilly.tk/~klein/RoRphotoblog.zip (Does not include the database 
file.)



A sincere thanks to everyone who can help! If you can only help with one 
of the two questions I''m still very thankful.
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