Auto-Expand div if textarea has content - php

Question

I am creating a blog using PHP / MySQL and there is an edit post function.
When clicking "Edit" the page "refreshes" (goes to the same page but the URL changes), the <div> expands and the text of the post they want to edit is now shown in the <textarea>.
With the help of another SO user I got part of this done. Only problem is that it's putting the editable text into every <texarea> box.
Here's a working example: http://thebulb.daysofthedead.net/testing.php
I have some thoughts on how to get this working but don't know how to do it since I am not good with jQuery or Ajax:
Add an ID to the <textarea> with the editable content and passing
that ID to the jQuery script.
Don't change pages, just use Ajax to
insert the text they want to edit into the <textarea>.
When they click "Edit" turn the box with the text into a <textarea> box with
submit form. I can get that part working by using an example I found
(http://jsfiddle.net/25Hay/2/) but I don't know how to submit that
to my PHP script for validation and insert into the database.
Here's the jQuery I currently use:
$(function(){
// Insert editable text into the <textarea> box
$('.blogcontainer textarea[name=postcontent]').filter(function(i) { return $.trim($(this).val()) != ""; }).closest('.postreplycontainer').slideDown("fast");
// Execute when Edit link is clicked
$(document).on('click', '.postreply', function(e) {
// Collapse all previous expanded <div>'s
$(this).closest('.blogcontainer').siblings('.blogcontainer').find('.postreplycontainer').slideUp("fast");
// Expand / Collapse <div>' when "Post Reply" is clicked
$(this).closest('.blogcontainer').find('.postreplycontainer').slideToggle("fast")
// Focus <textarea> when <div> is expanded
.find('textarea[name=postcontent]').focus();
});
});

Answer 1

1) Adding data-id to a textarea would be an easy approach. I see you already have post_id=5 in your URL when you want to edit a post, so I'm guessing you could use that (I can't find the script you use for updating the textareas)
2) and 3)
Ajax with jQuery is really easy to use. You can read more about it here http://api.jquery.com/jquery.ajax/
This is a JSFiddle example.
$.ajax({
url: '/echo/html/', // for JSfiddle only, here you will use the url that you normaly put in a form taget
data: {
textarea: textarea_value,
postID: post_id,
html: textarea_value // so jsFIDDLE can answer
}, // this is the data you send to that URL, in this case it's your value, in PHP you will then get them with $_POST['textarea'] or $_POST['postID']
type: 'post', // default is get, you can set it to post or head, text etc...
success: function (answer) {
// answer is what you get back from the server if the data was sent
alert(answer)
},
error: function () {
alert('something went wrong')
}
});