Zend Framework Data Layer Architecture

Question

I'm following the Zend QuickStart guide, and am a bit confused by the architecture for connecting to a database. I see 4 layers:

ModelClass
ModelClass_Mapper
ModelClass_DbTable
Actual MySQL Database

I've used an architecture before where there is one file that has properties that map directly to the database, and an extended class that holds all of the custom code for hooks and database action events.

Where can I find a good explanation of why it's necessary to have three files like this, instead of just having ModelClass inherit DbTable?

RockyFord · Accepted Answer · 2012-06-04 05:21:24Z

3

The ZF quickstart provides an example of The Data Mapper pattern that seems to work reasonably well with ZF 1.x. It is not required that you implement a Data Mapper to use Zend_Db. You can get quite good functionality just using the DbTable models and the methods provided by Zend_Db_Table_Abstract.

To explain a bit:

Application_Model_Guestbook: would be a simple Domain Model (the object you interact with).

Application_Model_GuestbookMapper: would be the data mapper to map the database columns to the propeties of the domain model.

Application_Model_DbTable_Guestbook: is the gateway model that provides the connection between the database and the database adapter. This is where you can specify options for your database table and relationships with other tables.

It took me a little experience with ZF and Models before I figured out how the data mapper applied to my applications. I really began to understand how these pieces fit together when I started building objects that depended on more then one database table.
'

You'll notice that a number of experienced ZF developers recommend Doctrine or some other ORM right away, for them that is probably the correct choice (and seems to be reflex for some). I just feel that I shouldn't start using an ORM until I understand at least the basics of what that ORM is doing.

[EDIT]

fetchAll() equivalent method in base mapper class, pass in instance of Zend_Db_Table_Abstract to the __constructor

public function findAll($order = NULL) {
        $select = $this->_getGateway()->select();
        if (!is_null($order)) {
            $select->order($order);
        }
        $rowset = $this->_getGateway()->fetchAll($select);
        $entities = array();
        foreach ($rowset as $row) {
            //abstract method required in each table mapper, this instantiates the domain model
            $entity = $this->createEntity($row);
            //identiy map allows lazy loading of certain members
            $this->_setMap($row->id, $entity);
            $entities[] = $entity;
        }
        //returns an array of domain models instead
        return $entities;
    }

the createEntity() method from of my table specific mappers

public function createEntity($row) {

        $data = array(
            'id'     => $row->id,
            'name'   => $row->name,
            'art'    => $row->art,
            'year'   => $row->year,                
        );

        $entity = new Music_Model_Album($data);
        //set artist id to reference map for lazy loading
        $entity->setReferenceId('artist', $row->artist_id);
        return $entity;
    }

Good Luck

edited Jun 4, 2012 at 5:21

answered Jun 1, 2012 at 10:39

RockyFord

8,5191 gold badge17 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

John Zumbrum Over a year ago

Okay, I get that the Application_Model_DbTable_Guestbook is really slim, and mostly contains stuff like the table name, and foreign key constraints, as well as providing common, non-sql dependent methods such as insert, update, etc. through inheritance.

John Zumbrum Over a year ago

I'm still confused as to the usage of the Application_Model_GuestBookMapper. In the example there are a few methods, fetchAll(), find(), that map from the db_table to the Guestbook object, but this seems to be violating DRY. Shouldn't this be done as a Mapper.Property = "StringNameofDBTableProperty"; or some such? Seems horribly inefficient to rewrite the mapping on every method, especially if the table column name is the same as the object property name.

RockyFord Over a year ago

In normal usage you would override these methods so you could create instances of your domain models instead of just getting the result set from the database. Very often a base class will work for most methods but would be extendable to handle variations in the data each model needed to perfrom the business logic. I added an example to my answer.

Config · Accepted Answer · 2012-06-01 08:09:40Z

2

A very good explanation is given here: http://martinfowler.com/eaaCatalog/dataMapper.html

A short quote:

The Data Mapper is a layer of software that separates the in-memory objects from the database. Its responsibility is to transfer data between the two and also to isolate them from each other. With Data Mapper the in-memory objects needn't know even that there's a database present; they need no SQL interface code, and certainly no knowledge of the database schema. (The database schema is always ignorant of the objects that use it.) Since it's a form of Mapper (473), Data Mapper itself is even unknown to the domain layer.

answered Jun 1, 2012 at 8:09

Config

1,69212 silver badges12 bronze badges

Comments

moteutsch · Accepted Answer · 2012-05-31 21:17:33Z

0

Personally, though I love the Zend Framework, I find the data layer libraries to be rather poor. What I now use is Doctrine combined with Bisna to integrate the two. Perhaps you should take a look at those as well?

answered May 31, 2012 at 21:17

moteutsch

3,8334 gold badges31 silver badges35 bronze badges

Comments

Ismael Vacco · Accepted Answer · 2012-05-31 22:28:10Z

0

The Zend_Db_Table solution is an implementation of the » Table Data Gateway pattern. The solution also includes a class that implements the » Row Data Gateway pattern.

You can look whose patterns in Table Data Gateway and Row Data Gateway

answered May 31, 2012 at 22:28

Ismael Vacco

1,0301 gold badge10 silver badges25 bronze badges

Collectives™ on Stack Overflow

Zend Framework Data Layer Architecture

4 Answers 4

3 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related