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File: fwphp/glomodul/mkd/02/01_fwphp/PHP_DIP_DI.txt
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Class: B12 PHP FW
Manage database records with a PDO CRUD interface
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Building a Basic Blog Domain Model Defining the relationships between domain objects, as well as their own rules, data, and behavior is up to the developer. Good OOP practices : involved objects have just a few, well-defined responsibilities, and model doesn't get its pristine (clean, pure) ecosystem polluted with database logic. Add to this that shifting the model from one infrastructure to another can be done in a fairly painless fashion, and you'll get to see why this approach is very appealing when developing applications that must scale well. ************************* 11111 ********************** February 24, 2012 By Alejandro Gervasio HOW TO CONSUME MODEL - Putting the Domain Model to Work blog domain model : underlying INTERFACES AND CLASSES living in happy ignorance about the existence of any type of persistence mechanism that may be implemented down the line, be it a database, a web service, or anything else network of rules and rich relationships with each other current domain object implementations can be replaced with custom ones without much fuss In this case each object graph is spawned by using plain Dependency Injection, which is sufficient for demonstrative purposes. If the situation warrants, however, object graph creation should be delegated to more versatile structures, such as a Dependency Injection Container or a Service Locator. In either case, at this point the model is already doing its business as expected. ************************* 22222 ********************** March 16, 2012 By Alejandro Gervasio Basic mapping module which will allow you to move data easily between the blog's model and a MySQL database, all while keeping them neatly isolated from one other. We'll be trying to connect a batch of mapping classes to a blog's domain model. Idea is to set up from scratch a basic Data Access Layer (DAL) so that domain objects can easily be persisted in a MySQL database, and in turn, retrieved on request through some generic finders. DAL in question will be made up of just a couple of components: the first one will be a simple database adapter interface, whose contract is interface DatabaseAdapterInterface. Contract allows us to create different database adapters at runtime and perform a few common tasks, such as connecting to the database and running CRUD operations without much fuss. Now we need at least one implementer of the interface that does all these cool things. The proud cavalier that will assume this responsibility will be a non-canonical class PdoAdapter implements DatabaseAdapterInterface. ALTER TABLE `admins` ADD `email` VARCHAR(60) NULL AFTER `username`; CREATE TABLE posts ( id INTEGER UNSIGNED NOT NULL AUTO\_INCREMENT, title VARCHAR(100) DEFAULT NULL, content TEXT, PRIMARY KEY (id) ); CREATE TABLE users ( id INTEGER UNSIGNED NOT NULL AUTO\_INCREMENT, name VARCHAR(45) DEFAULT NULL, email VARCHAR(45) DEFAULT NULL, PRIMARY KEY (id) ); CREATE TABLE comments ( id INTEGER UNSIGNED NOT NULL AUTO\_INCREMENT, content TEXT, user_id INTEGER DEFAULT NULL, post_id INTEGER DEFAULT NULL, PRIMARY KEY (id), FOREIGN KEY (user_id) REFERENCES users(id), FOREGIN KEY (post_id) REFERENCES posts(id) ); At this point we've implemented a simple DAL which we can use for persisting the blog's domain model in MySQL without sweating too much during the process. Now we need to add the middle men to the picture, that is data mappers, so any impedance mismatches can be handled quietly behind the scenes. Implementing a Bi-directional Mapping Layer - relational mappers Quite a ways away from being trivial. That's why ORM libraries like Doctrine live. Encapsulating as much mapping logic as possible within abstract class AbstractDataMapper - couple of generic finders, all of the logic required for pulling in data from a specified table, which is then used for reconstituting domain objects in a valid state. Because reconstitutions should be delegated down the hierarchy to refined implementations, the createEntity() method has been declared abstract. 5. Set of concrete mappers that will deal with blog posts, comments, and u sers : PostMapperInterface and class PostMapper extends AbstractDataMapper implements PostMapperInterface CommentMapperInterface and class CommentMapper extends AbstractDataMapper implements CommentMapperInterface UserMapperInterface and class UserMapper extends AbstractDataMapper implements UserMapperInterface PostMapper extends its abstract parent and injects in the constructor a comment mapper (still undefined), in order to handle in sync both posts and comments without revealing to the outside world the complexities of creating the whole object graph. CommentMapper class behaves quite similar to its sibling PostMapper. In short, it asks for a user mapper in the constructor, so that a specific comment can be tied up to the corresponding commenter. We build up from scratch an easy-to-manage mapping layer, capable of moving data back and forward between a simplistic blog domain model and MySQL. Mapping the Blog's Domain Objects to and from the DAL Mappers' APIs do the actual hard work and HIDE UNDERLYING DB FROM MODEL. This ability, though, is best appreciated from app. layer's perspective. Let's wire up all the mapper graphs together: ************************* 33333 If you have to write your own code to call the framework components, then it is not a framework, it is a library. A "true" FRAMEWORK IS MINI-APPLICATION TO GENERATE AND RUN YOUR APP COMPONENTS. Eg templating libraries to deal with creating markup, image libraries... Framework brings together all (or most) of the common functionality needed to build an app usually providing a more consistent API and often some of the boilerplate code to wire components together GENERATE AND RUN YOUR APP COMPONENTS fw definition is more definition of a Rapid Application Development (likely where Radicore gets its name) RAD framework, which is a PARTICULAR KIND OF FRAMEWORK, some of which allow u sers to build (or, more accurately, customize) an application via a GUI WITHOUT HAVING TO KNOW HOW TO PROGRAM. Of course, the apps you can build with such a framework are limited by the supplied components. I doubt you would be able to build an online image editing app, for example, using Radicore. What is SW fw (Software framework) provides a STANDARD WAY TO BUILD and deploy applications is abstraction in which SW providing GENERIC FUNCTIONALITY can be selectively applied / changed by additional user-written code, thus providing application-specific SW is universal, REUSABLE SW environment that provides particular functionality as part of a larger SW platform to facilitate development of SW applications key distinguishing features that separate SW fw from SW libraries IoC (INVERSION OF CONTROL) is key difference to a library: IoC is about who initiates control messages - DOES YOUR CODE CALL INTO A FW, or does it plug something into a framework, and then the framework calls back? Hollywood principle "Don't call us, we'll call you (details)." Eg game knows when a player can make decisions and prompts the player accordingly, rather than the player making the decision. Unlike in (set of) libraries intended to provide reuse or in normal user apps, CODE FLOW (OF CONTROL MESSAGES) IN SW FW IS DICTATED BY SW FW, not by the caller method. If you're using a library, objects and methods implemented by the library are instantiated and invoked by your custom app. You need to know which objects to instantiate / call. If you're using a framework, you implement objects and methods that are custom to your app and they are instantiated and invoked by fw. Fw defines the flow of control for app - embodies some abstract design, with more behavior built in. In order to use it you need to insert your behavior into various places in the framework either by subclassing or by plugging in your own classes. Fw code then calls your code at these points. DIP (Dependency Inversion Principle) high-level modules should not depend on Low-level modules, both should depend on abstractions abstractions should not depend on details, details should depend on abstractions Eg high-level module A --- uses ---> low-level module B. When applying DIP, both modules --- depend ---> on abstraction - interface, so A and B can be built, used, deployed independently (note that in UML diagrams all arrows point to dependency) Rationale When DIP is not applied, only the low-level modules can be reused independently. The higher-level modules depend on the others, so trying to reuse them makes it necessary to either also reuse the lower-level modules or to change the higher-level module. The former is often not wanted because reuse is often done in another context where the lower-level modules do not fit. And the latter is error-prone and requires additional work as it requires changes to already working modules. High-level module (your business logic), wants to be able to add or remove users to the DB. Instead of it talking to the database directly, it defines an interface called ClientRepository which contains the methods the business logic needs. Then a MySQLClientRepository concretion implements that interface and uses a database library to submit the queries. Since the interface is decided by the business logic, the high-level policy is protected from changes in the database library since the interface was defined by the business logic, it does not reveal anything about the underlying implementation, which allows different types of user repositories, such as a WebserviceClientRepository implementation (OCP) MySQLClientRepository and business logic can be built as well as deployed independently. class Mailer { // Methods for a Mailer class } class SendWelcomeMessage { private $mailer; public function __construct(Mailer $mailer) { // This is a violation of DIP as the method is relying upon a concretion rather than an abstraction. $this->mailer = $mailer; } } Term IoC was getting overloaded with different meanings - was the reason Fowler coined term DIP - early '90s. About libraries vs fws, inversion he's talking about is Hollywood principle "Don't call us, we'll call you (details)." 21 May 2013 Inversion is BOTTOMS UP DESIGN - reversal of direction in TOP-DOWN DESIGN : high-level design described by smaller parts and therefore it directly depends on them. Eg business requirement of reporting on energy savings depends on gathering data, which depends on executing Sql. Dependencies follow how the problem is decomposed. The more detailed something is, the more likely it will change. We have a high-level idea depending on something that is likely to change. In 2004, Martin Fowler published an article on Dependency Injection (DI) and Inversion of Control (IoC) . Is the DIP the same as DI, or IoC? No, but they play nice together. When Robert Martin first discussed DIP, he equated it a first-class combination of the Open Closed Principle and Liskov Substitution Principle, important enough to warrant its own name. DI is about wiring, IoC is about direction, and DIP is about shape. Dependency Injection is about how one object knows about another, dependent object (master table does not know about its details which have FK - knowlege about master). DI is about how one object acquires a dependency. IoC is about who initiates the call. If your code initiates a call, it is not IoC, if the container/system/library calls back into code that you provided it, is it IoC. DIP is about the level of the abstraction in messages sent from your code to the thing it is calling. To be sure, using DI or IoC with DIP tends to be more expressive, powerful and domain-aligned, but they are about different dimensions, or forces, in an overall problem. Several examples that all share common thread: raising abstraction level of a dependency to be closer to the domain, as limited by system needs. Hide DB Behind Something Domain-related A repository is a gateway to a conceptual (maybe actual) potentially large collection of durable objects. Typical interface might include basic CRUD operations (assuming the domain calls for them) but then we'll add methods that make sense for the needs of the system. Domain analysis is a form of Modeling. A key thing about modeling, is that you are only considering details that are important. Domain here is limited by some feature set rather than a mythical domain that exists outside of such context. In a sense, this is YAGNI applied to domain analysis. Not "best practices", but good ideas for a given context Design principles Should be "violated" sometimes Are often conflicting (at odds) with each other Often mix together for something even better than when used in isolation Often overlap with other ones There are no free lunches, all abstractions have a cost Like the term "best practices" I wonder if "design principles" even makes sense as a nikname (moniker = often a shortened name). In the case of the SOLID principles, I think of them more as up front ideas that I often come back to due to familiarity. I often fall back into the basics like COHESION and COUPLING, adding another level of indirection. By calling something a principle, when I'm pragmatic I will probably Preferable is to REPLACE "PRINCIPLE" WITH GUIDELINE. Whether we call something a principle or a guideline, the ability to make an informed decision to disregard a design principle (a so-called Journeyman behavior according to The Seven Stages of Expertise in Software, is a good place to strive towards. DIP like SOLID (five design principles intended to make software designs more understandable, flexible and maintainable) is simple to state but deep in its application. SOLID is subset of many principles stated by Robert C. Martin. Single responsibility principle - class should only have single r. that is, only changes to one part of the software's specification should be able to affect the specification of the class. Open-closed principle SW entities... should be open for extension, but closed for modification. Liskov substitution principle - Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program. See also design by contract. Interface segregation principle - Many client-specific interfaces are better than one general-purpose interface. Dependency inversion principle - One should "depend upon abstractions, [not] concretions See also : Code reuse Inheritance (object-oriented programming) Package principles DRY Don't repeat yourself GRASP (object-oriented design, not related to the SOLID design principle) General Responsibility Assignment Software Patterns (or Principles). Guidelines for assigning responsibility to classes and objects in OO Design. KISS principle (keep it simple, stupid - minimalist concept) YAGNI (You aren't gonna need it - ?ta ?e vam to npr excell a ne pdf izvje?taji) preprogramiravanje i preprojektiranje. Always implement things when you actually need them, never when you just foresee that you need them. YAGNI is a principle of XP (extreme programming), type of agile software development. HAS DEFAULT BEHAVIOR: must be some useful behavior and not a series of no-ops. NON-MODIFIABLE FW CODE: u sers should not modify SW fw code but can extend it EXTENSIBILITY: can be extended by the user usually by selective overriding or specialized by user code to provide specific functionality Component = Module like Oracle Forms .fmb tight group of related classes tasked with accomplishing a single task. components should be independent should SHARE A NAME SPACE so their classes don't need to make use statements to address each other. A task too small for a component is likely going to fall to a single class. Symfony's HttpFoundation is a good example - providing a basic I/O framework. It's not just used by Symfony, but also by Drupal 8, Laravel and Silex (that I know of). Packages or Bundles Packages are groups of related components. Twig is one example. Unlike a component which is usually a more or less drop it in decision, Packages tend to have more far reaching effects on the application since taking advantage of them will require some forethought and outside code will need to be aware of their API. The smallest frameworks and the largest packages is a very blurry line, frameworks style themselves to be more complete solutions than packages tend to be. Frameworks Frameworks provide a road map to solving a particular type of problem. There are general purpose frameworks - Symfony frameworks devoted to small scale websites - Silex and everywhere in between What makes Frameworks distinct from packages is they: Have a distinct over arching paradigm, either Model-View-Controller or Model-View-Presenter Have components and packages to implement the areas of that paradigm. Have a configuration methodology set up in PHP or non-PHP files, usually XML or INI or YAML. Largest frameworks are almost indistinguishable from apps and are ready to go from install, but the distinguishing line here is whether a non-programmer can be expected to set the code up and get it running. If not then, no matter how large and featured it is, it's still a framework, not an app. More framework can do, harder it is to customize it. This isn't always true though, and it also depends on what area of the app is being customized. The best frameworks tolerate having their components and packages switched out though the incoming packages will usually need a wrapper of some sort especially if the interface in that area hasn't been standardized. Apps If a non-programmer can be expected to install and configure the app without touching a single line of code then it's an App. Drupal 8 is one example, and a rather huge one at that. Apps may or may not have further customization possible, most popular ones have. The smaller apps out there can be smaller than some frameworks. The distinctive feature of an app is INSTALLER CODE that creates DB writes config file overall automates the setup process for a non-programmer user Frameworks don't have these though they might have tools for handling some parts of the install process, like creating blank model classes, route files or the like. Increasingly in the PHP world the leading applications bring together components and packages from various vendors. The only major PHP project that doesn't anymore is WordPress which can get away with this largely due to its marketshare - even then I've seen Wordpress plugins make use of component libraries. Given time even Wordpress will probably evolve over, though it's going to have to get rid of its horrid "The Loop" to do so. 44444 ********************** 08 May 2014 by Robert C. Martin (Uncle Bob) Breaking up a large piece of code into snippets : "sections" "modules" or "classes". Code is not responsible for bug fixes or refactoring but programmer is. To isolate your modules from the complexities of the organization, ee design your systems such that each module is responsible (responds to) the needs of just that one business function. : SRP (SINGLE RESPONSIBILITY PRINCIPLE) is about people (single person or tightly coupled group of people representing a single narrowly defined business function) who request method changes (many cooks spoil soup). Uncle Bob is saying that SRP has replaced SoC (SEPARATION OF CONCERNS) because SRP now includes ideas of Coupling and Cohesion which SoC did not. Ee: Gather together the things that CHANGE FOR THE SAME REASONS (PEOPLE !). Separate those things that change for different reasons. This is just another way to define cohesion and coupling. We want to increase the cohesion between things that change for the same reasons, and we want to decrease the coupling between those things that change for different reasons. Remember that the reasons for change are people. It is people who request changes. And you don't want to confuse those people, or yourself, by mixing together code that many different people care about for different reasons. This is the reason we SEPARATE CONCERNS (relevant things - responsibilities). Concern can be as general as details of HW the code is being optimized for, or as specific as name of a class to instantiate. we do not put SQL in JSPs we do not generate HTML in the modules that compute results business rules should not know the database schema Eg : public class Employee { public Money calculatePay(); //how much particular employee should be paid public void savePay(); //stores data managed by Employee object onto enterprise DB public String reportHours(); //returns string worked_number_of_hours } CEO = chief executive officer = chief operating officer = managing director =corporate executive responsible for the operations of the firm; reports to a board of directors; may appoint other managers (including a president) Reporting to that CEO are C-level executives eg : CFO = responsible for controlling the FINANCES of the company eg for calculatePay() COO = responsible for managing the OPERATIONS of the company eg for reportHours() CTO = responsible for the TECHNOLOGY infrastructure and development eg for savePay() 3-Tier Architecture - separating GUI logic, business logic and database logic is sufficient to satisfy SRP. Classes contain one method each, and each method contains one line of code : broken encapsulation low cohesion high coupling SRP == SoC + Coupling + Cohesion