Subversion-Projekte lars-tiefland.prado

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<h1>Creating Active Record Classes</h1>

<p>

We need to create two <a href="http://www.pradosoft.com/demos/quickstart/?page=Database.ActiveRecord">Active Record</a> classes, <tt>UserRecord</tt> and <tt>PostRecord</tt>, to represent data records in the <tt>users</tt> and <tt>posts</tt> tables, respectively. Active Record classes must extend from the base class <tt>ActiveRecord</tt>, and must define property names that matches with the field names of the corresponding table.

</p>

<p>

To better organize our directories, we create a new directory <tt>protected/database</tt> to hold the class files. We also modify our application configuration by inserting the following lines. It is equivalent to adding the directory <tt>protected/database</tt> to PHP include_path, which allows us to use the classes without explicitly including them.

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<paths>

  <using namespace="Application.database.*" />

</paths>

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<p>

Instead of writing the classes manually, we will use the <a href="http://www.pradosoft.com/demos/quickstart/?page=GettingStarted.CommandLine">PRADO command line tool</a> again to generate the classes for us.

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<p>

Under the <tt>blog</tt> directory, run the following command to enter into the interactive mode of the command line tool:

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php path/to/prado-cli.php shell .

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<p>

We should see

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Command line tools for Prado 3.1.0.

** Loaded PRADO appplication in directory "protected".

PHP-Shell - Version 0.3.1

(c) 2006, Jan Kneschke <jan@kneschke.de>

>> use '?' to open the inline help

>>

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<p>

At the prompt, enter the following two commands to create <tt>UserRecord</tt> and <tt>PostRecord</tt> classes:

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>> generate users Application.database.UserRecord

>> generate posts Application.database.PostRecord

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<p>

Here we used the <a href="http://www.pradosoft.com/demos/quickstart/?page=Fundamentals.Components">namespace format</a> again to specify the classes to be created. The path <tt>Application.database.UserRecord</tt> indicates that we want the <tt>UserRecord</tt> class file to be <tt>protected/database/UserRecord.php</tt>.

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<p>

We should see the following directory structure with two new files under <tt>protected/database</tt>:

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<img src="<%~ directories2.gif %>" class="output" />

<p>

If we check the <tt>PostRecord</tt> class file, we should see the following content.

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class PostRecord extends TActiveRecord

{

    const TABLE='posts';

    public $post_id;

    public $author_id;

    public $create_time;

    public $title;

    public $content;

    public $status;

    public static function finder($className=__CLASS__)

    {

        return parent::finder($className);

    }

}

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<p>

As we see, for each field in the <tt>posts</tt> table, the class has a corresponding data member. The constant <tt>TABLE</tt> specifies the table name for the <tt>PostRecord</tt>. The static method <tt>finder()</tt> allows us to perform query and retrieve post data in terms of <tt>PostRecord</tt> objects.

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<p>

We can use the command line tool to do some testing with our newly created Active Record classes. Still in the interactive mode of the command line tool, we enter a PHP statement and should see the following. Interested readers may try some other PHP statements, such as <tt>UserRecord::finder()->findAll()</tt>.

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>> PostRecord::finder()->findAll()

array

(

    [0] => PostRecord#1

    (

        [post_id] => '1'

        [author_id] => 'admin'

        [create_time] => '1175708482'

        [title] => 'first post'

        [content] => 'this is my first post'

        [status] => '0'

        [TActiveRecord:_readOnly] => false

        [TActiveRecord:_connection] => null

        [TComponent:_e] => array()

    )

)

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<h1>Relationship Between Posts and Users</h1>

<p>

Recall that there was a foreign key relationship between the <tt>users</tt> and <tt>posts</tt> table. The entity-relationship diagram is shown below for convienence.

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<img src="<%~ ER.gif %>" class="output" />

<p>

From the entity-relationship diagram above, we see that the <tt>posts</tt> table contains a field named <tt>author_id</tt>. This <tt>author_id</tt> field is a foreign key to the reference table <tt>users</tt>. In particular, the values in the  <tt>author_id</tt> field should be of that from the <tt>users</tt> table's <tt>username</tt> field. One of the consequence of this relationship, thinking in terms of objects, is that each "post" belongs to an "author" and one "author" may have many "posts".

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<p>

We can model the relationship between <tt>posts</tt> and <tt>users</tt> table in Active Record by modifying the <tt>PostRecord</tt> and <tt>UserRecord</tt> classes as follows.

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class PostRecord extends TActiveRecord

{

    //... properties and methods as before

    public $author; //holds an UserRecord

    public static $RELATIONS=array

    (

        'author' => array(self::BELONGS_TO, 'UserRecord'),

    );

}

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<p>

The static <tt>$RELATIONS</tt> property of <tt>PostRecord</tt> defines that the property <tt>$author</tt> belongs to an <tt>UserRecord</tt>. In <tt>array(self::BELONGS_TO, 'UserRecord')</tt>, the first element defines the relationship type, in this case <tt>self::BELONGS_TO</tt>. The second element is the name of related record, in this case an <tt>UserRecord</tt>. The <tt>UserRecord</tt> is defined similarly below, the difference is that, the user record has many <tt>PostRecord</tt>s.

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class UserRecord extends TActiveRecord

{

    //... properties and methods as before

    public $posts=array(); //holds an array of PostRecord

    public static $RELATIONS=array

    (

        'posts' => array(self::HAS_MANY, 'PostRecord'),

    );

}

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<p>

An array of <tt>UserRecord</tt> with and its corresponding posts may be fetched as follows.

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$users = UserRecord::finder()->withPosts()->findAll();

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The method <tt>withXXX()</tt> (where XXX is the relationship property name, in this case, <tt>Posts</tt>) fetches the corresponding <tt>PostRecords</tt> using a second query (not by using a join). The <tt>withXXX()</tt> method accepts the same arguments as other finder methods of TActiveRecord, e.g. <tt>withPosts('status = ?', 0)</tt>.

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<p>

Further detailed documentation can be found in the quickstart <a href="http://www.pradosoft.com/demos/quickstart/?page=Database.ActiveRecord">Active Record</a> docs.

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