Active Record
Active Records are objects that wrap a row in a database table or view,
encapsulates the database access and adds domain logic on that data.
The basics of an Active Record is a business object class, e.g., a
Products class, that match very closely the record structure
of an underlying database table. Each Active Record will be responsible for
saving and loading data to and from the database.
Info:
The data structure of an Active Record should match exactly that of a table
in the database.
Each field in the class must correspond to one column in the table.
When to Use It
Active Record is a good choice for domain logic that isn't too complex,
such as creates, reads, updates, and deletes. Derivations and validations
based on a single record work well in this structure. Active Record has the
primary advantage of simplicity. It's easy to build
Active Records, and they are easy to understand.
However, as your business logic grows in complexity, you'll soon want
to use your object's direct relationships, collections, inheritance, and so
forth. These don't map easily onto Active Record, and adding them piecemeal
gets very messy.
Another argument against Active Record is the fact that it couples the object
design to the database design. This makes it more difficult to refactor as a project goes forward.
The alternative is to use a Data Mapper that separates the roles of the
business object and how these objects are stored.
Prado provides a complimentary choice between Active Record and
SqlMap Data Mapper.
A SqlMap Data Mapper can be used to load Active Record objects, in turn, these
Active Record objects can be used to update the database.
The "relationship" between Active Records and SqlMap is illustrated in the
following diagram. More details regarding the SqlMap Data Mapper can be found in
the SqlMap Manual.
alt="Active Records and SqlMap DataMapper" id="fig:diagram.png" class="figure"/>
The Active Record class has methods that do the following:
- Construct an instance of the Active Record from a SQL result set row.
- Construct a new instance for later insertion into the table.
- Finder methods to wrap commonly used SQL queries and return Active Record objects.
- Update existing records and insert new records into the database.
The Active Record implementation utilizes the Prado DAO classes for data access.
The current Active Record implementation supports
MySQL,
Postgres SQL and
SQLite databases.
Support for other databases can be provided when there are sufficient demand.
Defining an Active Record
Let us
consider the following "users" table that contains two columns named "username" and "email",
where "username" is also the primary key.
CREATE TABLE users
(
username VARCHAR( 20 ) NOT NULL ,
email VARCHAR( 200 ) ,
PRIMARY KEY ( username )
);
Next we define our Active Record class that corresponds to the "users" table.
class UserRecord extends TActiveRecord
{
const TABLE='users'; //table name
public $username; //the column named "username" in the "users" table
public $email;
/**
* @return TActiveRecord active record finder instance
*/
public static function finder($className=__CLASS__)
{
return parent::finder($className);
}
}
Each property of the UserRecord class must correspond to a
column with the same name in the "users" table. The class constant
TABLE is optional when the class name is the same as
the table name in the database, otherwise TABLE must
specify the table name that corresponds to your Active Record class.
Note:
You may need to quote (specific to your database) the value of the TABLE.
E.g. MySQL uses back-ticks, TABLE = "`database1`.`table1`"
Since TActiveRecord extends TComponent, setter and
getter methods can be defined to allow control over how variables
are set and returned. For example, adding a $level property to the UserRecord class:
class UserRecord extends TActiveRecord {
... //existing definitions as above
private $_level;
public function setLevel($value) {
$this->_level=TPropertyValue::ensureInteger($value,0);
}
public function getLevel($value){
return $this->_level;
}
}
Info:
TActiveRecord can also work with database views by specifying the constant TABLE
corresponding to the view name. However, objects returned
from views are read-only, calling the save() or delete() method
will raise an exception.
The static method finder() returns an UserRecord instance
that can be used to load records from the database. The loading of records
using the finer methods is discuss a little later. The TActiveRecord::finder()
static method takes the name of the current Active Record class as parameter.
Setting up a database connection
A default database connection for Active Record can be set as follows.
See Establishing Database Connection for
futher details regarding creation of database connection in general.
//create a connection and give it to the ActiveRecord manager.
$dsn = 'pgsql:host=localhost;dbname=test'; //Postgres SQL
$conn = new TDbConnection($dsn, 'dbuser','dbpass');
TActiveRecordManager::getInstance()->setDbConnection($conn);
The default database connection can also be configured using a <module>
tag in the application.xml
or config.xml as follows.
Tip:
The
EnableCache attribute when set to "true" will cache the table
meta data, that is, the table columns names, indexes and constraints are
saved in the cache and reused. You must clear or disable the cache if you
wish to see chanages made to your table definitions. A
cache
module must also be defined for the cache to function.
A ConnectionID property can be specified with value corresponding
to another TDataSourceConfig module configuration's ID value. This allows
the same database connection to be used in other modules such as SqlMap.
Loading data from the database
The TActiveRecord class provides many convenient methods to find
records from the database. The simplest is finding records by matching primary keys.
See the for
more details.
findByPk()
Finds one record using only the primary key or composite primary keys.
$finder = UserRecord::finder();
$user = $finder->findByPk($primaryKey);
//when the table uses composite keys
$record = $finder->findByPk($key1, $key2, ...);
$record = $finder->findByPk(array($key1, $key2,...));
findAllByPks()
Finds multiple records using a list of primary keys or composite primary keys.
The following are equivalent for scalar primary keys (primary key consisting of only one column/field).
$finder = UserRecord::finder();
$users = $finder->findAllByPk($key1, $key2, ...);
$users = $finder->findAllByPk(array($key1, $key2, ...));
The following are equivalent for composite keys.
//when the table uses composite keys
$record = $finder->findAllByPks(array($key1, $key2), array($key3, $key4), ...);
$keys = array( array($key1, $key2), array($key3, $key4), ... );
$record = $finder->findAllByPks($keys);
find()
Finds one single record that matches the criteria. The criteria
can be a partial SQL string or a TActiveRecordCriteria object.
$finder = UserRecord::finder();
//:name and :pass are place holders for specific values of $name and $pass
$finder->find('username = :name AND password = :pass',
array(':name'=>$name, ':pass'=>$pass));
//using position place holders
$finder->find('username = ? AND password = ?', array($name, $pass));
//same as above
$finder->find('username = ? AND password = ?', $name, $pass);
//$criteria is of TActiveRecordCriteria
$finder->find($criteria); //the 2nd parameter for find() is ignored.
The TActiveRecordCriteria class has the following properties:
- Parameters -- name value parameter pairs.
- OrdersBy -- column name and ordering pairs.
- Condition -- parts of the WHERE SQL conditions.
- Limit -- maximum number of records to return.
- Offset -- record offset in the table.
$criteria = new TActiveRecordCriteria;
$criteria->Condition = 'username = :name AND password = :pass';
$criteria->Parameters[':name'] = 'admin';
$criteria->Parameters[':pass'] = 'prado';
$criteria->OrdersBy['level'] = 'desc';
$criteria->OrdersBy['name'] = 'asc';
$criteria->Limit = 10;
$criteria->Offset = 20;
findAll()
Same as find() but returns an array of objects.
findBy*() and findAllBy*()
Dynamic find method using parts of method name as search criteria.
Method names starting with findBy return 1 record only.
Method names starting with findAllBy return an array of records.
The condition is taken as part of the method name after findBy or findAllBy.
The following blocks of code are equivalent:
$finder->findByName($name)
$finder->find('Name = ?', $name);
$finder->findByUsernameAndPassword($name,$pass);
$finder->findBy_Username_And_Password($name,$pass);
$finder->find('Username = ? AND Password = ?', $name, $pass);
$finder->findAllByAge($age);
$finder->findAll('Age = ?', $age);
Tip:
You may also use OR as a condition in the dynamic methods.
findBySql()
Finds records using full SQL, returns corresponding array of record objects.
count()
Find the number of matchings records.
Inserting and updating records
Add a new record using TActiveRecord is very simple, just create a new Active
Record object and call the save() method. E.g.
$user1 = new UserRecord();
$user1->username = "admin"
$user1->email = "admin@example.com";
$user1->save(); //insert a new record
$data = array('username'=>'admin', 'email'=>'admin@example.com');
$user2 = new UserRecord($data); //create by passing some existing data
$user2->save(); //insert a new record
Tip:
The objects are update with the primary key of those the tables that contains
definitions that automatically creates a primary key for the newly insert records.
For example, if you insert a new record into a MySQL table that has columns
defined with "autoincrement", the Active Record objects will be updated with the new
incremented values.
To update a record in the database, just change one or more properties of
the Active Record object that has been loaded from the database and then
call the save() method.
$user = UserRecord::finder()->findByName('admin');
$user->email="test@example.com"; //change property
$user->save(); //update it.
Active Record objects have a simple life-cycle illustrated in the following diagram.
alt="Active Records Life Cycle" id="fig:cycle.png" class="figure"/>
We see that new ActiveRecord objects are created by either using one of the find*()
methods or using creating a new instance by using PHP's new keyword. Objects
created by a find*() method starts with clean state. New instance of
ActiveRecords created other than by a find*() method starts with new state.
When ever you
call the save() method on the ActiveRecord object, the object enters the clean
state. Objects in the clean becomes dirty whenever one of more of its
internal states are changed. Calling the delete() method on the object
ends the object life-cycle, no futher actions can be performed on the object.
Deleting existing records
To delete an existing record that is already loaded, just call the delete() method.
You can also delete records in the database by primary keys without
loading any records using the deleteByPk() method.
For example, to delete one or records with tables having a scalar primary key.
$finder->deleteByPk($primaryKey); //delete 1 record
$finder->deleteByPk($key1,$key2,...); //delete multiple records
$finder->deleteByPk(array($key1,$key2,...)); //delete multiple records
For composite primary keys (determined automatically from the table definitions):
$finder->deleteByPk(array($key1,$key2)); //delete 1 record
//delete multiple records
$finder->deleteByPk(array($key1,$key2), array($key3,$key4),...);
//delete multiple records
$finder->deleteByPk(array( array($key1,$key2), array($key3,$key4), .. ));
deleteAll() and deleteBy*()
To delete by a criteria, use deleteAll($criteria) and deleteBy*()
with similar synatx to findAll($criteria) and findAllBy*() as
described above.
//delete all records with matching Name
$finder->deleteAll('Name = ?', $name);
$finder->deleteByName($name);
//delete by username and password
$finder->deleteBy_Username_And_Password($name,$pass);
Transactions
All Active Record objects contains the property DbConnection
that can be used to obtain a transaction object.
$finder = UserRecord::finder();
$finder->DbConnection->Active=true; //open if necessary
$transaction = $finder->DbConnection->beginTransaction();
try
{
$user = $finder->findByPk('admin');
$user->email = 'test@example.com'; //alter the $user object
$user->save();
$transaction->commit();
}
catch(Exception $e) // an exception is raised if a query fails
{
$transaction->rollBack();
}
References
- Fowler et. al. Patterns of Enterprise Application Architecture,
Addison Wesley, 2002.
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