The Indicia warehouse code fulfills several objectives, including providing a user interface for managing the back-end data required for online recording as well as the web-services required to support the client websites. To do this, the code needs to respond to calls to certain web addresses, load information from the database, apply business logic and return appropriate output. Any development framework worth its salt aims to make development of this sort of application as simple as simple as possible, by
making the code easier to write.
limiting the amount of code you have to write so development is quick.
simplifying coding which tends to make things more reliable and easier to maintain.
The obvious way in which a framework can achieve these goals is to provide a set of classes or other library code which can perform the everyday tasks without you needing to write substantial amounts of code. The Kohana framework goes beyond being a simple library of useful code functions in several ways, not only because being an MVC framework, it expects you to split your code into models, views and controllers. Kohana also makes good use of on the principle of convention over configuration, that is, it relies on the notion that the developer should follow a set of conventions when writing code in order to allow Kohana to make certain assumptions. For example, in a traditional framework one might have to write a configuration file with content such as the following fictitious example in order to use a database access class:
This would enable the framework to work on the name of the PHP file to include and the class name to instantiate when it needs to load the class responsible for accessing survey data. There are several problems with this approach:
There is quite a lot of configuration to write to support the whole system.
There is a risk of inconsistency in the naming conventions, file locations and so forth. There is nothing stopping a model class being stored in a different folder or having a typo in the file name for example.
The principle of convention over configuration means that the Kohana framework avoids the necessity for extensive configuration files by publishing conventions regarding things like class names, file names and locations. The framework code can then be written with the assumption that the conventions are followed and because the code will simply not work if conventions are not followed, it forces consistency. It also saves time once the developer has learnt these conventions since there is no need to write the configuration for each thing you do. Rather than go into detail about all the conventions here you can read about them in the Kohana 101 documentation.
Folder Structure Conventions¶
There are a few conventions regarding the folder structure it would be handy to mention at this stage:
The Kohana framework code is kept in the system folder. This code should not be touched.
The code for the application you write is kept in the application folder.
Code for models (classes which provide access to an entity in the database) is kept in application/models.
Code for views (code which provide the user interface) is kept in the application/views folder.
Code for controllers (classes which provide business logice and the glue between models and views) is kept in the application/controllers folder.
The application can be extended by modules. Each module is represented by a single folder in the modules folder. Modules can contain their own models, views and controllers in subfolders of the same name.
When you write code that requires the Kohana framework to load a particular piece of code, Kohana will autoload the required PHP file. It will first look in the enabled modules, then the application folder, then the system folder. This means that modules can override existing application functionality by providing different versions of the code files.
How do URLs relate to controllers?¶
When you access a website, you do so by hitting certain web addresses which then return appropriate responses, normally HTML. Kohana has a simple convention allowing it to map web addresses you write. All web addresses actually go to a single PHP file called index.php in the root folder and the path given after this address dictates which bit of code is used to provide the response. For example there might be a web address available on your website:
When this web address is accessed, Kohana’s framework code will look through the
available controller code files for one called survey.php. It will first look in
the controllers folder for each of the enabled modules, then it will look in the
application/controllers folder, finally it will look in the system/controllers
folder. Once it finds the appropriate PHP file, it then loads the file and
attempts to create an instance of a class called
is the name we must give to our controller class for providing the ‘glue’
required for the database’s surveys table according to the Kohana conventions.
Once the class has been created, the Kohana framework code then calls the create method in the class, because if you look back at the URL we are accessing you will see that was the name given in the second part of the URL path. This method provided by the controller is often called the action. Therefore we could summarise the web addresses which our Kohana based site using the following pattern:
So, each controller declares a class with public methods that map to a single URL path in the application. The controller code is responsible for coordinating the database access logic in the model with the view template code to produce the required output.