Services, Mappers, Models: Enterprise Thinking in PHPAaron Saray - MKEPUG

Why trust this guy?● 21 years:

programmer● 12 years: internet

programmer● PHP Design

Patterns - WROX● Manager of Web

Team @ LPi

● So handsome

Disclaimer!!I don't have a BS CS. But that doesn't matter. Best practices exist in programming.Not everyone programs the same way.There is more than one way to solve a problem.Understand the core concepts, don't get hung up on the minutiae.For every solution I have, you can do it a different way too. Yours may work too!

What are we talking about today?● Services, Mappers, Models

○ Go by a few different names○ Mix and max

● Future proofing our solutions○ separation of concerns○ enterprise thinking

● Making life easier by investments up front

What are Models?● Represent a true entity in your business

○ user, visitor○ box, ps3, blu-ray movie

● They know about themselves in their current state○ they don't know if they're incomplete○ they don't know how they're populated

● Do logic from the business○ logical transformation that makes sense in your

realm

What are Models? (cont)Examples:

● User:○ first name, last name, age

■ calculates fullname■ calculates user requires adult consent

● PS3○ serial number, model number

■ calculates date manufactured from serial #

What are Models? (cont 2)Out of the realm of model:

● Have I been saved to the database?

● Have I been created from a form input or a MySQL result set?

● How can I get more information about myself?

What are Mappers?● Mappers map data to a model

● Mappers know about models. Models do not know about mappers.

● Mappers are dependent on the data source○ Swap data sources? Introduce a new mapper!

What are Mappers? (cont)● Mapper interprets a request and creates a

corresponding call to MySQL○ request for a package with ID #7, create MySQL call

for that, get results, apply to the model I received.

● Mapper applies data results to a model in the proper way

● Mappers are very foreign to most○ Most Frameworks provide generic ones with "magic"○ Most custom code lacks mappers

What are Services?● Services are the way that the rest of the

code requests objects

● Services know about a Model, and it's corresponding Mapper. Models and Mappers don't know about services.

● Services interpret requests, create new models, and invoke mappers to populate models.

What are Services? (cont)● Services understand logical identifiers of

models○ fetchById()

● Services can create containers or single result sets○ fetchPaginator(), fetchByEmail()

● Services retrieve and persist data○ fetching / saving / updating

What are Services? (cont2)● Services rarely change once created

○ Mappers change with new data sets○ Models change with new logic○ Retrieval methods are relatively stoic○ Persistence methods CAN change more often

Show me an example!

UserService::fetchById(5)

Show User Details for User # 5

UserMapper MySQL query ID = 5

new User();

Apply fetchAssoc to model

Yay!

Example Code:● It's easy for me to show you a perfect

situation○ But unless you're making something brand new, it's

not really feasible

● Let's look at some novice PHP code○ and refactor to Enterprise Thinking code!

What we're accomplishing?● Will use MySQL to retrieve user information

● Want to show the full name, email address, of user 5 on the screen

● Don't do this!

Controller Code

Class Code - Part 1

Class Code - Part 2

So What's Wrong With This?● From my introduction, you can spot some

things

● What are they?

Bad Things:

Seems like the User model is in charge of retrieving data based off the ID

More Bad Things

I'm not sure if this data is coming from the database - where the rest is. It's a one-off

Yup, the user has to populate itself, plus it has to understand that this is a key.

More Bad Things:

The model is now forever tied to the data source, and must be modified if it changes.

Here logic is being done in the model. That's fine. However, it's using map-able data. :(

The model is mapping itself to the data set results. If a data source is changed, even the creation of "full name" is lost.

Save me!● Model should be only concerned with itself

○ full name is logic

● Mapper should connect and retrieve MySQL data and apply it to the model

● Service should be initialized in the controller and retrieve the proper user of ID 5

A Simpler User Model

Creating a full name is actually a logical calculation. For example, American name, this is correct. Latino heritage full name may contain multiple last names.

No population. Only stores data, and calculations (see below).

Mapper for MySQLOnly for MySQL - this is important!!

Mapper creates connection.

Mapper understands ID, but has to receive a new user instance. Can't create one itself.

Retrieve data, and apply it to the object.

User Service

Initialize a User for the mapper.

Get new mapper. Send to mapper the user and the data access pointer(user id).

Return the properly populated model to the requestor.

Updated Controller CodeInstead of creating a new User object, create a new service object. Then, ask the service for the user of ID #5.

Don't forget! The full name is not really a property - so now it's a method call in our code.

What was gained?● Model now only deals with business

information

● Service can easily ask for and interpret requests for particular models

● Bound our mapper to MySQL○ made it easier to swap out data sources

Ruh Roh!● Requirements change!

● Choose your poison:○ your boss said to new partner "it won't be a big deal,

of COURSE we can use your feed instead of our database"

○ your client says "omg omg omg we now need to use this feed because it's the newest thing do it now!"

Requirement Change:Instead of using MySQL, now all user data must be retrieved from a XML feed request.

Using a GET request, call the feed URL with a parameter of the user ID.

You can expect an XML document with one node with the attribute as the ID, and nodes for the user information.

What We Used to Have to Do● Back in the day

○ Open up the User class and modify code○ Possibly delete old code and lose it○ Modify the model even though nothing has changed○ Cry

What we will do now● Create a new mapper class named after the

Remote XML feed○ note: we don't have to get rid of any old code

■ what if boss changes his mind back?

● Change one line in Service class

● To summarize:○ One line change of existing code○ Rest is brand new code

■ SUCH A SMALL IMPACT

Fine: I did change the controller

The only change is including the new file instead. A good autoloader would have made this a non-issue. But, I had to show you this. Ignore it as a required 'change'

One line change in Service

See? Simple little change. If I want to go back to the old code, I can change this mapper back.

New Mapper Class

Same method call, just different data retrieval and preparation.

Final Thoughts● Probably should create a mapper interface -

so that all mappers now have a mapFromId() method

● It is easy to swap back and forth with different data sources

● Business req changes are now easier○ least impact on each individual part

The End

Questions?

Aaron SarayMilwaukee PHP Web Developer

http://aaronsaray.com

@aaronsaray