From In-Portal Developers Guide

Revision as of 00:48, 12 April 2009

Системные классы
Статьи в этой категории
Работа с классом kDBItem KHTTPQuery

The kDBItem class is one of the base classes. It provides methods for working with data. Events are widely used to connect between objects of the kDBItem and other parts of the system. Events occurring during the execution of methods of the kDBItem class can be перехватывать - hooked (is this correct?) to execute needed actions. The other way around is also possible - the system has events whose execution triggers execution of methods of the kDBItem class.

Loading from the Database

The method Load is used to load data from the database. The method returns true if data was loaded successfully and false otherwise. If there is a need to check whether a single object was successfully loaded from the database, then the method isLoaded can be used, which returns the status (true or false) of loading the last object. Requirements for loading data are defined as the parameters of the method and can be simple or complex.

A simple requirement would be where the first parameter is the value of one of the fields of a record. Usually it's an Integer value of the primary key, in which case a second parameter isn't needed. If the value of a different field is passed in the first parameter, then the second parameter must be the name of the corresponding field.

// Obtain a reference to the object. The third parameter prevents the automatic load of data to the object
$user =& $this->Application->recallObject('u', null, Array('skip_autoload' => true));
/* @var $user kDBItem */
 
// Load the data of the object with ID = 23
$user->Load(23);
 
// Here there may be actions with the object
 
// Load user data to the object by his e-mail address
$user->Load('erik@intechnic.com', 'Email');

A complex requirement for loading data from the database can be where the first parameter passes an array containing the field names as keys and, as values, the values that should be in the corresponding fields of the loaded record.

$load_keys = Array(
	'FirstName' => 'Erik',
	'LastName' => 'Snarski'
);
 
$user->Load($load_keys);

As a result, to load this data, an SQL-query will be used with the following conditions:

WHERE FirstName = 'Erik' AND LastName = 'Snarski'

Changing Data

SetField and SetDBField are used to change the value of a field. SetDBField enters the value of the $value variable into the field exactly as it's passed. SetField before entering the record checks whether a formatter is assigned for the field, and if one is assigned, transforms the value of the field using the formatter's Parse method.

// For example, with formatting a date
$user->SetField('dob', '12/22/1971');
// The result will be the same as
$user->SetDBField('dob', 62197200);

Often, it's convenient to change the data for several fields at once. For example, to overwrite the value of several fields, that were received as a result of a form submission. For that we have the SetFieldsFromHash and SetDBFieldsFromHash functions. They accept an array as a parameter, that contains the names of the fields and the values for them. SetFieldsFromHash, just like the above SetField, calls the formatter's Parse method to transform a value.

$field_values = Array(
	'Email' => 'erik@intechnic.com',
	'FirstName' => 'Erik',
	'LastName' => 'Snarski',
	'dob' => '12/22/1971'
);
// Usually, an array like this is received from a request constructed like this
$items_info = $this->Application->GetVar( $event->getPrefixSpecial(true) );
list ($id, $field_values) = each($items_info);
 
// and, finally,to record the values into the object
$user->SetFieldsFromHash($field_values);

Sometimes, for example when importing data, we have to reuse the same object of the kDBItem class with different sets of data. The Clear method can be useful in such cases, which sets default values for all fields, thus guaranteeing that each data set will contain only its own data.

Discovering Changed Fields

Often, when changing an object's data, it's useful to check which fields were changed and which weren't. For example, if some actions only need to be performed if certain fields were changed. It's possible to get the value of a field before it was changed, right after loading the data from the database, with the help of the GetOriginalField method.

Valdiation

The Validate method is used to check an object's data. If, during the execution of the method, a discrepancy between data and requirements for the data is found, the object's FieldErrors property will contain an array, with the names of the fields used as key top-level elements, appended to second-level elements with the 'pseudo' keys. These are error codes that summarize the nature of the problem. It's possible to check whether a method has such error codes with the HasErrors method.

Error codes can be found in the debugger by opening it after an unsuccessful attempt to save data.

[Name] = Array
        (
            [pseudo] = required
        )

Sometimes it's necessary to not only make note of error information concerning fields, but to record it. For example, when writing functions that validate data that are specific to a particular programming problem. In that case, to represent an error in a field, the kDBItem class provides the SetError method.

For example, when editing data in a form, it's possible to choose a category from a list to which the object belongs. However, before saving to the database, it's a good idea to make sure that a category with such an ID really exists:

/**
 *
 * @param kEvent $event
 */
function OnBeforeItemUpdate(&$event)
{
	$object =& $event->getObject();
	/* @var $object kDBItem */
 
	$category_id = $object->getDBField('CategoryId');
	if (!$category_id) {
		// value not passed - validation not needed
		return;
	}
 
	if ($category_id == $object->GetOriginalField('CategoryId')) {
		// value did not change - validation not needed
		return;
	}
 
	$sql = 'SELECT COUNT(*)
		FROM ' . $this->Application->getUnitOption('c', 'TableName') . '
		WHERE ' . $this->Application->getUnitOption('c', 'IDField') . ' = ' . $this->Conn->qstr($category_id);
	if (!$this->Conn->GetOne($sql)) {
		$object->SetError('CategoryId', 'invalid_category', 'la_error_InvalidCategory');
	}
}

Saving to the Database

The methods Create and Update are used to save to the database. The Create method is for creating a new record. The Update method - for changing an existing record. By default, both of these methods, before saving data to the database, perform a valdiation using the Validate method, and make a record only if validation is successful. In the below example, a data import is being done and if the data of the user being created don't validate, then a record simply won't be created.

// Place data from an outside source into an array
$sql = 'SELECT username, password, email
	FROM user';
$users = $application->Conn->Query($sql);
 
// Create an object of the kDBItem class
$user =& $application->recallObject('u.-item', null, Array('skip-autoload' => true));
/* @var $user kDBItem*/
 
foreach ($users AS $user_data) {
	// Set default values by calling the Clear method
	$user->Clear();
 
	// Set field values for the record being imported
	$user->SetDBField('Login', $user_data['username']);
	$user->SetDBField('Email', $user_data['email']);
	$user->SetDBField('Password', $user_data['password']);
	$user->SetDBField('VerifyPassword', $user_data['password']);
 
	// Call the Create method to create the record in our system
	$user->Create();
}

Using Events

The four main methods of the kDBItem class that can directly connect to the database are:

• Create;
• Load;
• Update;
• Delete.

Each of these methods in certain situations calls events that can be used to connect an object of the kDBItem class with the rest of the system. All four of these methods can, while executing, call the events OnBeforeItem**** and OnAfterItem****, where **** is the name of the method. The OnBeforeItem**** event gets called before making the change in the database. The OnAfterItem**** event is called only after successfully performing the action in the database.

The Create and Update methods can also call the OnAfterItemValidate event. This happens in the case where a validation of the object's data was performed and the validation was successful. The OnAfterItemValidate is called before a query is made to the database. Below is an example of how the OnAfterItemDelete event can be used to perform additional actions after successfully deleting a record.

function OnAfterItemDelete(&$event)
{
	$object =& $event->getObject();
	/* @var $object kDBItem */
 
	// Despite the record in the database already being deleted, all its data is kept in memory and
	// depending on the value of the fields of the deleted record, it's possible to execute various actions
	$topic_id = $object->GetDBField('TopicId');
	if (!$topic_id) {
		// deleting non-existing post
		return ;
	}
 
	$post_helper =& $this->Application->recallObject('PostHelper');
	/* @var $post_helper PostHelper */
 
	// update posts count in topic
	$post_helper->updatePostCount($topic_id, -1);
}

Key Events That Use kDBItem Class

The key events that use the kDBItem class are located in the kDBEventHandler class.

These events, as a rule, are initialized from the web page, i.e. their names are passed in a request to the server.

• The OnNew event occurs when a form for entering new data to create a new record is opened.
• OnCreate - when sending data to the server to create a new record.
• OnUpdate - when sending data to the server to change existing record.

function OnUpdate(&$event)
{
	// Get a reference to an object of the kDBItem class.
	$object =& $event->getObject( Array('skip_autoload' => true) );
 
	// Get data from the request.
	$items_info = $this->Application->GetVar( $event->getPrefixSpecial(true) );
	if ($items_info) {
		foreach ($items_info as $id => $field_values) {
			// Load data from the database by its ID
			$object->Load($id);
 
			// Insert data from the request into the object.
			$object->SetFieldsFromHash($field_values);
 
			$this->customProcessing($event, 'before');
 
			// Call method from the kDBItem class.
			if ( $object->Update($id) ) {
				$this->customProcessing($event, 'after');
				$event->status=erSUCCESS;
			}
			else {
				$event->status=erFAIL;
				$event->redirect=false;
				break;
			}
		}
	}
	$event->setRedirectParam('opener', 'u');
}

See Also

• Debugger
• Formatters
• Hooks