OOP - Advice on calling classes within classes

leatherback

Hi All,

After years of basic 'linear' PhP programming, where I defined most standard actions in functions, but no classes were used, I now have a project which I am using as a testbed for OOP.

To start with, I got a database class from the web (MySQL Singleton Class to allow easy and clean access to common mysql commands by ricocheting; http://www.ricocheting.com/). This is used to perform all sorts of database actions.

Now I am creating a class 'data_array' which I will use to store and manipulate all data that comes in arrays. in specific, I would like to extend this to a child class: 'label'. This will hold arrays with labels and ID values from lookup tables. Very usefull if you process large volumes of data, and you just want to get the ID values of your categorization labels for instance.

OK, enough about what I am building. The questions:

Am I correct in thinking that OOP main strong point compared to linear programming (But with all standard routines captured in functions) lays in the 'memory' of the objects; e.g., you can easily store and retreive information in an organized way?
When I need to insert a label, because the label is unknown, I need to call the database class to perform the insert operation. Would this fit within good OOP practice? That you create a database object within a class definition?

So, would this be ok to do:

Class Label extends data_array {

Public function InsertLabel($name)
  {
  $db = Database::obtain($db_host, $db_user, $db_password, $db_name);
  $db->connect();
  $recordid = $db->updateinsert(_LABEL_T_, $name, 'l_value');
  $db->close();
  // set label to array
  }

If not: How would one add a label to the database here?

laserlight

What is a label and what does it mean to insert a label?

leatherback

Basically a lookup table for categories etc:

Category label: "technology", with label ID = 1

Then:

item.id = item_to_cat_table.itemnr | item_to_cat_table.catnr = category.id

laserlight

Just to check: have you read any material on object oriented design?

It looks like your InsertLabel method should either be a static method that creates a label with the given name and updates the database, or it should not take a $name argument; rather, the constructor should take a $name argument.

leatherback

Hi Laser,

thanks for your input. This was just an example as to where I might need a database class, not the actual stuff I will put in there. So, yes. I have read up on OOP, and one of the things I read is that a class should not be dependent on outside classes. Therefore my question how to deal with the database layer.

laserlight

leatherback wrote:
This was just an example as to where I might need a database class, not the actual stuff I will put in there.

Then you would need to be clear as to what exactly is this database class, e.g., it is just meant to provide a uniform interface like PDO, or to provide an abstraction layer, etc.

leatherback wrote:
So, yes. I have read up on OOP, and one of the things I read is that a class should not be dependent on outside classes.

What does "should not be dependent on outside classes" mean to you? What do you understand concerning loose coupling?

leatherback

The database class provides general functions such as query(), insert, update, etc and handles my error capturing.

As for loose coupling: I have no idea what that means.

What I read is that a class should not need any outside classes to function. Which -if this is true- I could not call my database class from within my array handling class..?

laserlight

leatherback wrote:
The database class provides general functions such as query(), insert, update, etc and handles my error capturing.

Ah, then it is probably more like PDO, i.e., meant to provide an abstraction of the database programming interface, though not of the functionality.

leatherback wrote:
What I read is that a class should not need any outside classes to function.

That is not true. It is true that in an ideal world, a class should not need to know about any concrete classes, but it would typically make use of some kind of interface that the relevant concrete class(es) implement, e.g., an interface construct or an abstract base class.

leatherback wrote:
As for loose coupling: I have no idea what that means.

I suggest that you read these articles (in PDF format). C++ is the language used, but the concepts are applicable in PHP:
Open-Closed Principle
Liskov Substitution Principle
Dependency Inversion Principle
Interface Segregation Principle

Derokorian

Hey laserlight thanks for the great links. =D

/end-thread-hijacking

leatherback

ok, will do. Thx.