I'll admit, I haven't unit tested much... but I'd like to. With that being said, I have a very complex registration process that I'd like to optimize for easier unit testing. I'm looking for a way to structure my classes so that I can test them more easily in the future. All of this logic is contained within an MVC framework, so you can assume the controller is the root where everything gets instantiated from.
To simplify, what I'm essentially asking is how to setup a system where you can manage any number of third party modules with CRUD updates. These third party modules are all RESTful API driven and response data is stored in local copies. Something like the deletion of a user account would need to trigger the deletion of all associated modules (which I refer to as providers). These providers may have a dependency on another provider, so the order of deletions/creations is important. I'm interested in which design patterns I should specifically be using to support my application.
Registration spans several classes and stores data in several db tables. Here's the order of the different providers and methods (they aren't statics, just written that way for brevity):
Provider::create('external::create-user') initiates registration at a particular step of a particular provider. The double colon syntax in the first param indicates the class should trigger creation on providerClass::providerMethod. I had made a general assumption that Provider would be an interface with the methods create(), update(), delete() that all other providers would implement it. How this gets instantiated is likely something you need to help me with.
$user = Provider_External::createUser() creates a user on an external API, returns success, and user gets stored in my database.
$customer = Provider_Gapps_Customer::create($user) creates a customer on a third party API, returns success, and stores locally.
$subscription = Provider_Gapps_Subscription::create($customer) creates a subscription associated to the previously created customer on the third party API, returns success, and stores locally.
Provider_Gapps_Verification::get($customer, $subscription) retrieves a row from an external API. This information gets stored locally. Another call is made which I'm skipping to keep things concise.
Provider_Gapps_Verification::verify($customer, $subscription) performs an external API verification process. The result of which gets stored locally.
This is a really dumbed down sample as the actual code relies upon at least 6 external API calls and over 10 local database rows created during registration. It doesn't make sense to use dependency injection at the constructor level because I might need to instantiate 6 classes in the controller without knowing if I even need them all. What I'm looking to accomplish would be something like Provider::create('external') where I simply specify the starting step to kick off registration.
The Crux of the Problem
So as you can see, this is just one sample of a registration process. I'm building a system where I could have several hundred service providers (external API modules) that I need to sign up for, update, delete, etc. Each of these providers gets related back to a user account.
I would like to build this system in a manner where I can specify an order of operations (steps) when triggering the creation of a new provider. Put another way, allow me to specify which provider/method combination gets triggered next in the chain of events since creation can span so many steps. Currently, I have this chain of events occurring via the subject/observer pattern. I'm looking to potentially move this code to a database table, provider_steps, where I list each step as well as it's following success_step and failure_step (for rollbacks and deletes). The table would look as follows:
# the id of the parent provider row
provider_id int(11) unsigned primary key,
# the short, slug name of the step for using in codebase
step_name varchar(60),
# the name of the method correlating to the step
method_name varchar(120),
# the steps that get triggered on success of this step
# can be comma delimited; multiple steps could be triggered in parallel
triggers_success varchar(255),
# the steps that get triggered on failure of this step
# can be comma delimited; multiple steps could be triggered in parallel
triggers_failure varchar(255),
created_at datetime,
updated_at datetime,
index ('provider_id', 'step_name')
There's so many decisions to make here... I know I should favor composition over inheritance and create some interfaces. I also know I'm likely going to need factories. Lastly, I have a lot of domain model shit going on here... so I likely need business domain classes. I'm just not sure how to mesh them all together without creating an utter mess in my pursuit of the holy grail.
Also, where would be the best place for the db queries to take place?
I have a model for each database table already, but I'm interested in knowing where and how to instantiate the particular model methods.
Things I've Been Reading...
Design Patterns
The Strategy Pattern
Composition over Inheritance
The Factory method pattern
The Abstract factory pattern
The Builder pattern
The Chain-of-responsibility pattern
You're already working with the pub/sub pattern, which seems appropriate. Given nothing but your comments above, I'd be considering an ordered list as a priority mechanism.
But it still doesn't smell right that each subscriber is concerned with the order of operations of its dependents for triggering success/failure. Dependencies usually seem like they belong in a tree, not a list. If you stored them in a tree (using the composite pattern) then the built-in recursion would be able to clean up each dependency by cleaning up its dependents first. That way you're no longer worried about prioritizing in which order the cleanup happens - the tree handles that automatically.
And you can use a tree for storing pub/sub subscribers almost as easily as you can use a list.
Using a test-driven development approach could get you what you need, and would ensure your entire application is not only fully testable, but completely covered by tests that prove it does what you want. I'd start by describing exactly what you need to do to meet one single requirement.
One thing you know you want to do is add a provider, so a TestAddProvider() test seems appropriate. Note that it should be pretty simple at this point, and have nothing to do with a composite pattern. Once that's working, you know that a provider has a dependent. Create a TestAddProviderWithDependent() test, and see how that goes. Again, it shouldn't be complex. Next, you'd likely want to TestAddProviderWithTwoDependents(), and that's where the list would get implemented. Once that's working, you know you want the Provider to also be a Dependent, so a new test would prove the inheritance model worked. From there, you'd add enough tests to convince yourself that various combinations of adding providers and dependents worked, and tests for exception conditions, etc. Just from the tests and requirements, you'd quickly arrive at a composite pattern that meets your needs. At this point I'd actually crack open my copy of GoF to ensure I understood the consequences of choosing the composite pattern, and to make sure I didn't add an inappropriate wart.
Another known requirement is to delete providers, so create a TestDeleteProvider() test, and implement the DeleteProvider() method. You won't be far away from having the provider delete its dependents, too, so the next step might be creating a TestDeleteProviderWithADependent() test. The recursion of the composite pattern should be evident at this point, and you should only need a few more tests to convince yourself that deeply nested providers, empty leafs, wide nodes, etc., all will properly clean themselves up.
I would assume that there's a requirement for your providers to actually provide their services. Time to test calling the providers (using mock providers for testing), and adding tests that ensure they can find their dependencies. Again, the recursion of the composite pattern should help build the list of dependencies or whatever you need to call the correct providers correctly.
You might find that providers have to be called in a specific order. At this point you might need to add prioritization to the lists at each node within the composite tree. Or maybe you have to build an entirely different structure (such as a linked list) to call them in the right order. Use the tests and approach it slowly. You might still have people concerned that you delete dependents in a particular externally prescribed order. At this point you can use your tests to prove to the doubters that you will always delete them safely, even if not in the order they were thinking.
If you've been doing it right, all your previous tests should continue to pass.
Then come the tricky questions. What if you have two providers that share a common dependency? If you delete one provider, should it delete all of its dependencies even though a different provider needs one of them? Add a test, and implement your rule. I figure I'd handle it through reference counting, but maybe you want a copy of the provider for the second instance, so you never have to worry about sharing children, and you keep things simpler that way. Or maybe it's never a problem in your domain. Another tricky question is if your providers can have circular dependencies. How do you ensure you don't end up in a self-referential loop? Write tests and figure it out.
After you've got this whole structure figured out, only then would you start thinking about the data you would use to describe this hierarchy.
That's the approach I'd consider. It may not be right for you, but that's for you to decide.
Unit Testing
With unit testing, we only want to test the code that makes up the individual unit of source code, typically a class method or function in PHP (Unit Testing Overview). Which indicates that we don't want to actually test the external API in Unit Testing, we only want to test the code we are writing locally. If you do want to test entire workflows, you are likely wanting to perform integration testing (Integration Testing Overview), which is a different beast.
As you specifically asked about designing for Unit Testing, lets assume you actually mean Unit Testing as opposed to Integration Testing and submit that there are two reasonable ways to go about designing your Provider classes.
Stub Out
The practice of replacing an object with a test double that (optionally) returns configured return values is refered to as stubbing. You can use a stub to "replace a real component on which the SUT depends so that the test has a control point for the indirect inputs of the SUT. This allows the test to force the SUT down paths it might not otherwise execute". Reference & Examples
Mock Objects
The practice of replacing an object with a test double that verifies expectations, for instance asserting that a method has been called, is referred to as mocking.
You can use a mock object "as an observation point that is used to verify the indirect outputs of the SUT as it is exercised. Typically, the mock object also includes the functionality of a test stub in that it must return values to the SUT if it hasn't already failed the tests but the emphasis is on the verification of the indirect outputs. Therefore, a mock object is lot more than just a test stub plus assertions; it is used a fundamentally different way".
Reference & Examples
Our Advice
Design your class to both all both Stubbing and Mocking. The PHP Unit Manual has an excellent example of Stubbing and Mocking Web Service. While this doesn't help you out of the box, it demonstrates how you would go about implementing the same for the Restful API you are consuming.
Where is the best place for the db queries to take place?
We suggest you use an ORM and not solve this yourself. You can easily Google PHP ORM's and make your own decision based off your own needs; our advice is to use Doctrine because we use Doctrine and it suits our needs well and over the past few years, we have come to appreciate how well the Doctrine developers know the domain, simply put, they do it better than we could do it ourselves so we are happy to let them do it for us.
If you don't really grasp why you should use an ORM, see Why should you use an ORM? and then Google the same question. If you still feel like you can roll your own ORM or otherwise handle the Database Access yourself better than the guys dedicated to it, we would expect you to already know the answer to the question. If you feel you have a pressing need to handle it yourself, we suggest you look at the source code for a number a of ORM's (See Doctrine on Github) and find the solution that best fits your scenario.
Thanks for asking a fun question, I appreciate it.
Every single dependency relationship within your class hierarchy must be accessible from outside world (shouldn't be highly coupled). For instance, if you are instantiating class A within class B, class B must have setter/getter methods implemented for class A instance holder in class B.
http://en.wikipedia.org/wiki/Dependency_injection
The furthermost problem I can see with your code - and this hinders you from testing it actually - is making use of static class method calls:
Provider::create('external::create-user')
$user = Provider_External::createUser()
$customer = Provider_Gapps_Customer::create($user)
$subscription = Provider_Gapps_Subscription::create($customer)
...
It's epidemic in your code - even if you "only" outlined them as static for "brevity". Such attitiude is not brevity it's counter-productive for testable code. Avoid these at all cost incl. when asking a question about Unit-Testing, this is known bad practice and it is known that such code is hard to test.
After you've converted all static calls into object method invocations and used Dependency Injection instead of static global state to pass the objects along, you can just do unit-testing with PHPUnit incl. making use of stub and mock objects collaborating in your (simple) tests.
So here is a TODO:
Refactor static method calls into object method invocations.
Use Dependency Injection to pass objects along.
And you very much improved your code. If you argue that you can not do that, do not waste your time with unit-testing, waste it with maintaining your application, ship it fast, let it make some money, and burn it if it's not profitable any longer. But don't waste your programming life with unit-testing static global state - it's just stupid to do.
Think about layering your application with defined roles and responsibilities for each layer. You may like to take inspiration from Apache-Axis' message flow subsystem. The core idea is to create a chain of handlers through which the request flows until it is processed. Such a design facilitates plugable components which may be bundled together to create higher order functions.
Further you may like to read about Functors/Function Objects, particularly Closure, Predicate, Transformer and Supplier to create your participating components. Hope that helps.
Have you looked at the state design pattern? http://en.wikipedia.org/wiki/State_pattern
You could make all your steps as different states in state machine and it would look like graph. You could store this graph in your database table/xml, also every provider can have his own graph which represents order in which execution should happen.
So when you get into certain state you may trigger event/events (save user, get user). I dont know your application specific, but events can be res-used by other providers.
If it fails on some of the steps then different graph path is executed.
If you will correctly abstract it you could have loosely coupled system which follows orders given by graph and executes events based on state.
Then later if you need add some other provider you only need to create graph and/or some new events.
Here is some example: https://github.com/Metabor/Statemachine
I am trying to use the new Eventmanager of the Zend Framework 2. I do understand the basic usage. But i´m not sure how to use this in a real project or rather where to go with the code.
For example:
In the introduction from Rob Allen (link above) he triggers two events in the "findById" Method. Where should the code for the listeners go to? In my opinion it doesn´t make sense to put this code also in the PhotoMapper class or am i wrong?
I confess that I have not played with it strongly yet, but I think you are right that the listener code should probably not be in the mapper. Rather, it can stand alone in an external class so it can really be a single-responsibility object - handling the events to which he subscribes - and the code can stay as DRY as possible.
As a first step, we can define what the listener needs to to do his job. Some things he knows on instantiation, others need to passed when the event is triggered.
For example, for a cache listener, I might instantiate him at Bootstrap with info about where to cache, lifetime, etc. Perhaps even grab a cache instance fully configured and ready to go from the cachemanager resource. These could be constructor params for the listener object.
Then, still probably at Bootstrap, I would register this listener with the event manager, subscribing to your event and attaching the method you wish to run when the event is triggered. Of course, that method signature needs to be compatible with the information that the event manager will give you.
I guess the idea is that this listener object has the potential benefits of:
being single-responsibilty, so lower complexity and easier to test
hopefully being sufficiently general so that this single listener can handle multiple events.
There is a little wrinkle here. It might seem like unreasonable performance hit to instantiate and register a listener just on the chance that some downstream process might trigger the event to which he is subscribed. That's where static listeners come in. Again, the registration is done early (like Bootstrap), but the listener is not instantiated until he is really needed.
Disclosure: I might have this completely wrong. So if someone wants to straighten me out, that would be great. ;-)
In PHP 5.2.x, mySQL 5.x
Im having a bit of an issue wrapping my head around what should and should not be an instance of a class in php because they are not persistent once the page is rendered.
Say I have a list of comments. To me, it would make sense that every comment be its own object because I can call actions on them, and they hold properties. If I was doing this in another language (one that has persistent state and can be interacted with), I would do it that way.
But it seems wasteful because to do that I have a loop that is calling new() and it would probably mean that I need to access the database for each instance (also bad).
But maybe im missing something.
Php just seems different in how I think about class and objects. When should something be a class instance, and when not?
This is a subjective issue, so I'll try to gather my thoughts coherently:
Persistence in PHP has sort of a different meaning. Your thinking that each comment should be an object because comments have actions which can be performed on them seems correct. The fact that the objects won't persist across a page load isn't really relevant. It isn't uncommon in PHP to use an object in one script, which gets destroyed when the script completes, and then re-instantiate it on a subsequent page load.
Object-oriented programming provides (among other things) code organization and code reuse. Even if an object is only really used once during the execution of a script, if defining its class aids in program organization, you are right to do so.
You usually needn't worry about resource wastefulness until it starts to become a problem; if your server is constantly taxed to where it degrades your user experience or limits your expansion, then it is time to optimize.
Addendum:
Another reason defining a class for your comments is that doing so could pay dividends later when you need to extend the class. Suppose you decide to implement something like a comment reply. The reply is itself just a comment, but holds some extra attributes about the comment to which it refers. You can extend the Comment object to add those attributes and additional functionality.
An Observer Design Pattern is the solution to loosely coupling objects so they can work together. In PHP you can easily implement this using just two classes.
Basically, you have a subject which is able to notify and update a list of observers of its state changes.
The problem I'm trying to solve is to know how to handler alerting the observers about different states of the object they are watching.
For example, lets say we have a file upload class to which we attach a logging class, websockets class, and a image resize class. Each of these classes that are watching want to know about different events in the upload process.
This file upload class might have three places where it needs to notify the classes listening that something has happend.
Error With Upload (alert logging class)
Upload success (alert websockets class)
Upload success and is image file (alert image resize class)
This is a very basic example, but how do you handle multiple events that different observers may need to know about? Calling notifyObservers() alone wouldn't be enough since each observer needs to know what it is being notified about.
One thought is that I could state with the call what type of event is being observed:
$this->notifyObservers('upload.error', this);
However, that would mean I would have to add custom switching to the observers themselves to know how to handle different events.
function observe($type, $object)
{
if($type === 'upload.error') $this->dosomething();
elseif($type === 'something.else') $this->otherthing();
...etc...
}
I find that very ugly as it starts to couple the observers back to the class they are observing.
Then again, if I just notify Observers without passing any information about what event just happens - they have to guess themselves what is going on which means more if() checks.
The observers aren't actually coupled to the class they are observing. The connection between the observer's handler and the observed object is made using literal string values (e.g. `upload.error'), which means that:
If you want to observe a specific object, you have to know from beforehand the names of the events it will publishing; this is the "coupling" that you don't like.
On the other hand, if you are interested in a specific event only, you can observe any type of object for that event without having any knowledge about that object.
Item 2 above is a benefit that you care about, but what to do about item 1?
If you think about it, there needs to be some way to differentiate between callbacks to the same observer if they represent different events taking place. These "identifiers", no matter what form they take, need to be packaged either into the observed object or be a part of the observer library code.
In the first instance (inside observed object) you would probably need a way for observers to query "do you ever publish event X?" before starting to observe a target for that event. The target can answer this question just fine. This leaves a bitter taste of coupling, but if you want any object to observe any other, and you have no idea what you will be observing beforehand, I don't think you can do any better.
In the second approach, you would have a number of well-known events defined (as const inside a class?) in your library. Presumably such a list of events can be made because the library tackles a concrete application domain, and that domain offers obvious choices for the events. Then, classes both internal to your library (which would end up being observed) and external to it (the observers which plug into the framework) would use these identifiers to differentiate between events. Many callback-based APIs (such as Win32) use an approach practically identical to this.
Dang-I know this is a subjective question so will probably get booted off/locked, but I'll try anyway, because I don't know where else to ask (feel free to point me to a better place to ask this!)
I'm just wrapping my head around oop with PHP, but I'm still not using frameworks or anything.
I'd like to create several small simple objects that I could use in my own websites to better get a feel for them.
Can anyone recommend a list or a resource that could point me to say 10 day-to-day objects that people would use in basic websites?
The reason I'm asking is because I'm confusing myself a bit. For example, I was thinking of a "database connection" object, but then I'm just thinking that is just a function, and not really an "object"??
So the question is:
What are some examples of objects used in basic PHP websites (not including "shopping cart" type websites)
Thanks!
Here's a few basic reusable objects you might have:
Session (identified by a cookie, stored server side)
User (username, password, etc.)
DBConnection (yes, this can be an object)
Comment (allow users to comment on things)
It sounds like you want to start to build your own web framework, which is a decent way to learn. Don't reinvent the wheel though. For a production site, you're probably better off using an existing framework.
Since you said you don't want to glue HTML and CSS again, you don't try this:
Create a WebForm class. This class is a container of form elements. It has methods to add and remove form elements. It has a getHTML() method that writes the form so that the user can input data. The same object is when a POST is made. It has a method to validate the input of the user; it delegates the validation to every form element and then does some kind of global validation. It has a process method that processes the form. It is final and checks whether validation has passed. If it passed it calls an abstract protected method that actually does the form-specific processing (e.g. insert rows into the DB). The form may be stored in the stored in session, or it may be re-built everytime (if it is stored in the session, it's easier to make multi-page forms).
Create a BaseFormElement and then several child classes like EmailElement, PhoneElement etc. These have also a getHTML() method that is called by WebForm::getHTML() and that prints the specific element. They have a validate() method that is called by WebForm::validate() and a getData() method that returns the properly validated and processed data of that element.
These are just some ideas. Some things may not make sense :p
I'd say database access would be the first most likely object - encapsulate your most common SQL requests into one class. If you make them abstract enough, you can use them for a wide variety of data access situations.
The way to think about class design/usage is to think of the class responsibility. You should be able to describe the class purpose in a short sentence (shorter than this...) i.e for database access object, you might say:
"provides API for common data access tasks"
If any of the methods in your data access class do something other than that, then you know they belong somewhere else.