Finance on Rails Finale

Hi all,

It's been a while since a post has been made. We've finished our thesis and have officially graduated!

I'm now working in a company called First Rate doing SEO/SEM consulting.

This blog will now be officially inactive so please visit my new website at http://www.dannytalk.com/.

It's been fun and I hope this blog has helped users with MySQL and Ruby on Rails related problems!

Disable Foreign Key Check Under MySQL

Mysql::Error: #23000Cannot add or update a child row: a foreign key constraint fails
(`depot_development/line_items`, 
CONSTRAINT `fk_items_product` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`)
ON DELETE CASCADE): INSERT INTO line_items (`quantity`, `product_id`, `id`,
`unit_price`) VALUES (1, 1, 1, 29.95)

OR

ActiveRecord::StatementInvalid: Mysql::Error: 
Cannot delete or update a parent row: a foreign key constraint fails: 
DELETE FROM line_items WHERE id = 1

If you've ever gotten the above error message from unit testing with Rails, this is what you gotta do.

Turn off constraints when fixtures are loaded to run unit tests by adding the following to the end of test_helper.rb:

class Fixtures
  def delete_existing_fixtures_with_fk_checks_disabled
    @connection.update "SET FOREIGN_KEY_CHECKS = 0" 
    delete_existing_fixtures_without_fk_checks_disabled
    @connection.update "SET FOREIGN_KEY_CHECKS = 1" 
  end

  def insert_fixtures_with_fk_checks_disabled
    @connection.update "SET FOREIGN_KEY_CHECKS = 0" 
    insert_fixtures_without_fk_checks_disabled
    @connection.update "SET FOREIGN_KEY_CHECKS = 1" 
  end

  alias_method_chain :delete_existing_fixtures, :fk_checks_disabled unless method_defined?(:delete_existing_fixtures_without_fk_checks_disabled)
  alias_method_chain :insert_fixtures, :fk_checks_disabled unless method_defined?(:insert_fixtures_without_fk_checks_disabled)
end

Read more about it here.

Testing Stage

Seems like I've pretty much finished my coding. Perhaps a little bit of tweaking now and there.

Will begin to write up testing reports and fix any bugs that arises. Also commenting all of my code as I go along.

Marko and I will be integrating our code together tomorrow as he needs my user function and also my stylesheet.

8 days to go...

Gruff Graph Customisation

I've just managed to get my graph customisation up and running. You can now graph three different types of graph: pie, stackedbar and sidestackedbar.



The variables that you can customise are the width of the image in pixels, (automatically sets it to 4:3 ratio), graphing by project or job, data breakdown and specified flow.



Not all of these customisations are available to all graphs but the javascript control handles what the user can select. Different graphs work differently.

The way a pie graph handles data is by accepting a number, attached with the data identifier.

# Example of adding data to a pie graph.
g.data("Data Identifier", 50)

The way a sidestackedbar/stackedbar graph handles data is by accepting an array of values, attached with the data identifier.

# Example of adding data to a sidestackedbar/stackedbar graph.
g.data("Data Identifier", [1, 2, 5])

Of course there are so many other customisations that can be implemented but I don't think I have time to implement them. This will do for now.

For Gruff API reference, click here. Gruff samples can also be seen here.

Syntax Highlighter

I've just installed Google's Syntax Highlighter. This javascript allows you to highlight codes without formatting it manually.

To use, simply do

<pre name="code" class="language">
...some code here...
</pre>

A wiki of usage can be found here.

NOTE: One important thing to watch out for is opening triangular bracket <. It must be replaced with an HTML equivalent of < in all cases. Failure to do won't break the page, but might break the source code displayed.

Here's a list of supported languages and their aliases:

Language	Aliases
C++	cpp, c, c++
C#	c#, c-sharp, csharp
CSS	css
Delphi	delphi, pascal
Java	java
Java Script	js, jscript, javascript
PHP	php
Python	py, python
Ruby	rb, ruby, rails, ror
Sql	sql
VB	vb, vb.net
XML/HTML	xml, html, xhtml, xslt

Converting binary data to image in HTML

Let's say you were making an Ajax request for an image, and the response is a base64 encoded string which you want to use to create an image in HTML. A way of doing so is to use "data:image/png;base64," at the start of your image source, and append the encoded string.

For example,

<img='data:image/<image format>;base64,<encoded string>' />

This will correctly render the encoded string into an image that can be displayed on the browser.

Using Gruff to create graphs, the Gruff::Base has a method called to_blob which draws the graph and returns the graph as a rendered binary. Simply return a base64 encoded version of it to the Ajax call to be processed.

# Controller
g = Gruff::Pie.new(300)
.
.
.

render :text => encode64(g.to_blob)

Creating hover menus and closing them with Javascript + Prototype

First of all I created an empty div that will be used to contain my menu contents. For example,

<div id="accesslist" class="accessmenu">Hello there!</div>

With CSS,

div.accessmenu {
    position: absolute;
    background: #F5F5F5;
    border: 1px solid #888;
    margin: 0;
    padding: 3px;
    visibility: hidden;
}

Now it's up to you how you want to position the menu, but this is how I did it with Javascript.

$('accesslist').style.left = Position.positionedOffset(el)[0];
$('accesslist').style.top = Position.positionedOffset(el)[1] + el.offsetHeight;
$('accesslist').style.zIndex = 10;
$('accesslist').style.visibility = 'visible';

The code above will place the div directly below element 'el'. Now the problem is how do you close the menu when you click away from it? A simple solution can be found using prototype's Event class.

Event.observe(document.body, 'click', function(e) {
    if (!Element.descendantOf(Event.element(e), $('accesslist')))
        $('accesslist').style.visibility = 'hidden';
});

What this code does is that it observes 'click' events that occur on the document.body. The third function parameter checks if the event click happened on my menu element's descendants (i.e. down the tree hierarchy). If not, then close the menu.

Simple.