Entities are simply the code reprentations of the main concepts in your application, the data structures you're going to be working with.

When designing an app, you probably have a set way of doing things, but chances are you're going to:

OO design makes complex application design more manageable by providing the following concepts:

DB_DataObject is a package from PEAR that takes care of entity management for you. In the words of the author Alan Knowles:

DataObject performs 2 tasks:

The core class is designed to be extended for each of your tables so that you put the data logic inside the data classes. Included is a generator to create your configuration files and your base classes.

At one time or another your web application is going to require you to manage your entities in some way, usually modifying the object state by performing one the the following basic operations:

The term in parentheses is the SQL analogy. What DataObjects (DO) does is to encapsulate the way you interact with your data, making it a lot easier to manage object state. The package has the following workflow:

DB_DataObject Version 0.3 introduced the ability to create link ini files so you can map rows to other database columns using an ini file. This ini file should have the name '(databasename).links.ini', and be placed in the (Seagull)/var/cache/entities/ folder.

The (databasename).links.ini file contains a section for each table, then the primary and foreign key mappings for each.

If you use a 'full stop' in the key (link from column), getLinks() will look up in the table with the field name matching the string to the left of the 'full stop', and replace the 'full stop' with an underscore and assign the object variable to that name. Or you may wish to use the selectAs() method to decide how you want columns from different objects to be returned, when using joinAdd().

;       for table person
[person]
;       link value of eyecolor to table colors, match name column
eyecolor = colors:name
;       link value of owner to table grp, match id column
owner = grp:id
;       link value of picture to table attachments, match id column
picture = attachments:id

;       for a sales example with multiple links of a single column
[sales]
;       for autoloading the car object into $sales->_car_id
car_id = car:id
;       for autoloading the part number object into $sales->_car_id_partnum
car_id.partnum = part_numbers:car_id

$person = new DataObjects_Person();
$person->eyeColour = 'red';
$person->find();
while ($person->fetch()) {

// use the links.ini file to automatically load
// the car object into $person->_car
$person->getLinks();

    echo "{$person->name} has red eyes and owns a {$person->_car->type}\n";
}

// and finally the most complex, using SQL joins and select as.
// the example would look like this.

$person = new DataObjects_Person();
$person->eyeColour = 'red';

// first, use selectAs as to make the select clauses match the column names.
$person->selectAs();

// now lets create the related element
$car = new DataObjects_Car();

// and for fun.. lets look for red eys and red cars..
$car->colour = 'red';

// add them together.
$person->joinAdd($car);

// since both tables have the column id in them, we need to reformat the query so
// that the car columns have a different name.
$person->selectAs($car,'car_%s');

$person->find();
while ($person->fetch()) {
    echo "{$person->name} has red eyes and owns a {$person->car_type}\n";
}