The MVC principle in web programming. Public protective signs

In the room

protective element- Watermark: tradition and innovation

meeting point- This is the money of tomorrow

point of view- Premieres and trends

know-how- Two-faced defense

know-how- The whole secret is in the lenses

document- Canadian Passport: The Art of Technology

development- Protective fibers: new possibilities

stamps- Tiles, nickel and Brodsky's poems

signs of history- Postcards: the path from “postal telegram” to propaganda poster

excursion- Armenian dramas: money illustrates history

Easy to check, hard to repeat

IN last years Goznak actively develops and markets the most effective protective technologies. Among them, two directions stand out: to create elements visible to light, and features obtained through a combination of offset and metallography

Today, the banknote industry is in greater demand than ever for effective technological and security solutions. In recent years, Goznak has been paying special attention to the development and promotion to the market of such solutions, the concept of which can be formulated as follows: the development of security features that are easy to identify, but difficult to reproduce, obtained using standard equipment. We will illustrate this approach to the development of effective security technologies using the example of the development of two directions: obtaining optically variable features visible through transmission, and features obtained through a combination of offset and intaglio printing.

Enlightened Technologies

A watermark, observed in paper in transmitted light, remains the most popular security feature among the population. At the same time, it is technologically advanced, and the experience of producing paper with watermarks dates back to more than seven centuries. That is why in recent years, thanks to the emergence of new technologies for the manufacture of uniform products, this protective feature has received a new development. Multi-tone watermarks in almost all modernized banknotes have given way to watermarks obtained by combining multi-tone and filigree marks. And currently, the technology for obtaining watermarks using complex multi-level filigree is being actively implemented. The Watermark magazine has repeatedly talked about these watermarks. This technology makes it possible to obtain not only contrasting light areas of the mark, but also images with a high lineature, atypical for watermarks.

Security threads, like transmission-controlled watermarks, have, unlike the latter, a not so long history - a little more than a century and a half. However, they are firmly established at the top level of security technology. This is due both to the good manufacturability of paper with security threads and to their the broadest possibilities act as a carrier of various protective characteristics and effects. Despite the seemingly undeniable advantages over watermarks, the significantly higher cost of the security threads themselves reduces the effectiveness of their use, especially at low denominations, where, as a rule, the simplest and, accordingly, cheaper thread options are used. That is why one of the directions in the development of security threads at Goznak was the production of a large-area transparent window in paper by introducing a wide transparent polymer tape during paper casting, followed by the use of standard printing technologies to obtain protective effects in the window area. Since the polymer film from which the tape is made is a mass-produced product and does not contain exclusive protective features, its cost is significantly lower than the cost of threads that have color-variable, optically variable and other high-tech features. At the same time, similar highly secure optically variable features can be obtained using traditional printing technologies, which makes this technical solution more efficient.

This is exactly the approach that was implemented in the Sochi 2014 commemorative banknote. In a transparent window, obtained by introducing a wide polymer tape into the paper during low tide, an optically variable protective element “Zebra” is made using a metallographic method. When viewed in the light and smoothly rotate the banknote, you can see how the image of a snowflake in the window changes from negative to positive.

What if you do not introduce a polymer tape to obtain an optically variable feature controlled by transmission? Or, in another way, how to obtain a transmission-controlled optically variable element in paper using traditional banknote technologies? This is exactly the task that was set for the employees of the Directorate for protective technologies and specialists from the Goznak Research Institute in 2014. The goal is obvious: to get rid of the “additional” element - a wide polymer tape and the complex technology of its introduction into paper, i.e. to make security solution even more effective.

The task turned out to be very difficult, since, on the one hand, the final result was influenced a large number of factors, and, on the other hand, the main factors turned out to be not only closely related to each other, but also were in conflict with each other. We had to look for non-standard solutions. By the end of 2014, after research work, the fundamental possibility of obtaining such protective elements was proven. In 2015, FSUE Goznak issued an advertising banknote “Russian Avangard”, presented by the deputy general director on science and development by A. B. Kuryatnikov in the second issue of the magazine “Watermark” for 2015. The advertising banknote implements the “Silhouette” security element - an optically variable element, visible in transmitted light and made using traditional printing banknote technologies in a translucent window obtained using traditional technology making banknote paper. Currently, work is being carried out to improve the technology for obtaining a translucent window, and to optimize the design of printed elements.

Dice game

MVC, MVC+, HMC... These abbreviations for the names of security features developed at FSUE Goznak have regularly appeared on the pages of the magazine since 2004. And if you collect all the articles written on this topic, you will get a whole story of the birth, formation and development of one of the most effective, in our opinion, protective areas. The peculiarity of this direction is that to reproduce security elements, a combination is used in the form of geometrically coordinated lines printed by offset and intaglio printing methods.

The MVC Moire Variable Color security feature that appeared in the modernized banknotes of the Bank of Russia was intended primarily for copy protection. Let us recall how the feature works: on an initially homogeneous field, when the banknote is tilted, moire colored stripes appear. This optically variable effect is absent on the copy, i.e., either colored moire stripes do not appear, or are detected immediately, and the picture remains unchanged no matter how the banknote is tilted or rotated. The potential of this feature turned out to be much higher than originally expected due to its high resistance to imitation, manufacturability, wear resistance and the possibility of its further modernization. The simplicity of its implementation in banknotes of the city modernization series of 2004 and the rapid imitations expected by Goznak specialists in this regard forced the modernization of this security feature in the direction of creating a moiré pattern that is more difficult for counterfeiters to reproduce, due to the use of a nonlinear line structure and the use of a combination of inkless embossing and colorful intaglio print. This is how the next generation of the optically variable feature MVC+ appeared. This security element has two coordinated areas. In the lower area, the moire pattern is visible from any angle, and in upper area, as with MVC, it only appears at a certain angle. It is very important to know that when tilting the banknote, the moire pattern of the upper and lower parts should form one continuous picture without shifting the moire lines at the border of these two areas. In addition, this protective feature is enhanced by the cash level of protection. When viewing an MVC+ element under UV light, you can observe exactly the same moiré effect as in daylight. The MVC+ security element is used in Bank of Russia banknotes in denominations of 1000 and 5000 rubles, modernized in 2010.

In parallel with MVC+, development was carried out on a new protective element with greater visual effect. And by 2010, a new security feature, HMC (Hidden Multi Color), was created, which became an even more effective security element in this series of features. Due to the change in the geometric parameters of the offset and metallographic lines when the banknote is tilted, the initially homogeneous field is divided into separate fragments painted in different colors. Numbers, text symbols, geometric figures, any arbitrary areas. Usually no more than 2-3 colors are used. An important feature of this protective feature is the ability additional check its authenticity. If you remember the colors visible when the banknote is tilted, and then turn the banknote in its plane 180 degrees, you can see completely different colors of the fragments. This effect is achieved thanks to the special shape of the lines and the use of unique equipment for the manufacture of metallographic forms. Like the MVC+ element, the HMC security element has an additional cash level of authentication: when exposed to UV light, you can see exactly the same optically variable effects as in daylight. The HMC security element was introduced into the security complex of the Bank of Russia 500 ruble banknote of the 2010 modification.

To obtain protective elements of the MVC - HMC series, metallographic lines with a sufficiently large relief depth are used. Under very high pressure conditions during intaglio printing, the paper is deformed, taking the shape of the profile of intaglio lines. The resulting relief appears on both the front and back sides of the printed sheet. While the front side relief “works” in the security features of the MVC – HMC series, the reverse side relief was not used until recently. Goznak specialists proposed an interesting solution - the creation of optically variable elements on both the front and back sides of the banknote using intaglio printing only on the front side. Such an element was developed and implemented on the advertising banknote “195 years of Goznak”. Detailed description this element, called CHMC (Combined HMC), is given in the magazine “Watermark” No. 3 for 2013. In addition to obtaining optically variable features on both sides of the banknote through the use of an important technological feature of the offset printing machine - ensuring accurate registration of front and back printing sides - an element has been obtained to control the alignment of the front and back sides. Thus, CHMC is “three in one”, i.e. optical features on both sides of the banknote and an element to control the alignment of the front and back sides. An important feature of this element is that both MVC and HMC or a combination of both can be obtained independently on the front and back sides of the banknote. Thus, on the advertising banknote “Russian Avangard” the HMC element is used on the front side, and a combination of MVC and HMC is used on the reverse side.

To obtain the best visual effect when creating MVC - HMC series features, especially HMC, it is necessary to use bright, contrasting colors when printing offset lines. The ideal case is to use CMY colors. However, often when upgrading banknotes, the customer does not allow colors to be changed or such bright colors to be used for offset printing. Therefore, a compromise has to be made between design and visual effect. This is especially true for the HMC element. It is for such “complex” banknotes in terms of color that two- and even single-color optically variable HMC elements were developed. In this case, a one-color element is formally two-color, since a space, i.e., the color of the paper, is used as the second paint. Therefore, when the banknote is tilted, the color does not change; a positive or negative image appears.

In addition, any of the elements of the MVC - HMC series can be supplemented with a hidden or latent image.

Thus, today a series of effective optically variable protective elements produced by a combination of offset and intaglio printing has been created. This is a kind of set of cubes that can be used to build a unique security complex for various banknotes.

The development of optically variable protective elements of the MVC - HMC series continues. There are new ideas. And it is quite possible that a new implementation of a security feature based on a combination of offset and intaglio printing will soon appear in a new advertising banknote or any circulation product.

Application development according to the template MVC design(model-view-controller) is typical for Java and, when applied to DroidScript, seems incomprehensible and unnecessary. Why complicate everything? MVC acquired an aura of complexity and “magic” due to the use of beautiful but incomprehensible words (concept, model, business logic, pattern) and complex demonstrations in the context of Java when considering it. Everything is much simpler: MVC is one of the design patterns that produces additionalcode sharing in object-oriented environment.

The central element of the MVC model is the controller - normal application DroidScript, from which the code related to the visual markup and appearance of widgets, as well as data and methods for accessing them, are derived. By data we are accustomed to understanding information stored in arrays, files, and databases. But in concept MVC data are understood in the broad sense of the word - this is everything that is not application code:

• external data from files and databases - metadata, text, graphics, sounds, music, etc.
• internal application data - lines with labels on buttons and other controls, text in dialog boxes, description of styles, constants, software generated graphics, etc.

From the user's point of view, his experience with the application does not change when using MVC: he also clicks on buttons, selects data and how it is displayed. Changes may concern facilities this work. And on the development side, the changes are noticeable: the interaction between data and its display in the MVC concept occurs through the controller and under its control.

Let's first look at a simple example of using MVC in a single-file application.

Single-file implementation of the MVC model

Let's take a simple application.

Function OnStart())( var _lay = app.CreateLayout("linear", "VCenter,FillXY"); var _btnShowVersion = app.CreateButton("Show version", 0.3, 0.1); _btnShowVersion.SetBackColor("#66778976"); _btnShowVersion.SetMargins(0, 0.05, 0, 0); _btnShowVersion.SetOnTouch(function())( _btnShowVersion.SetText("Application version 1.0"); ));

At first glance, everything seems good, but suppose that you need to change color scheme applications and display text in several languages. This will lead to complications, since all the data in the example shown are fixed values ​​(literals). This significantly reduces the flexibility of the code and complicates its debugging and support.

Another drawback is that the data - the labels on the button, the markup - methods for displaying widgets, and the action - the block of code that changes the label on the button when it is clicked are located in one block and in one file. That is, to change the label you need to open this file and gain access to the entire application code. It's like changing a car tire requires disassembling the body of the car to gain access to all the contents. For what? During the process of disassembling the car body, you can accidentally catch something and render it inoperative. It is also possible in the code: I wanted to replace the line name in one place, but the replacement occurred throughout the entire file, which led to a scattering of errors. Or you just wanted to change the color of the button, but accidentally caught the code nearby and the entire application stopped working.

One of the tasks of the MVC pattern is precisely to differentiate access: first, the module (or block of code) that is the source of the error is identified, and then access is given only to it. Why give access to the electronics and engine of a car if you need to change a tire?

If development is carried out in one file, then this often happens like this: new functions are placed in place, at the very beginning or end of the code, which over time leads to their mixing. Let’s add here the mixing of code in the functions themselves, and in a month even with comments it will be difficult to understand all this.

Let's implement the example shown above in the context of MVC. To do this, all the code needs to be divided and grouped in appropriate blocks. The order of the blocks in the code is not important, but it is better to adhere to the logic: for the controller to work, both data and elements for displaying them are necessary, so it is placed last. When the data is displayed, it must exist. This means that the model block comes first:

1. Model
2. Performance
3. Controller

//+++ model (function())( var _obj = ; //+++ data var _version = "Application version 1.0"; var _titleShowVersion = "Show version"; //--- data
//+++ public methods for accessing data _obj.getVersion = function())( return _version; ) _obj.btnGetTitle = function())( return _titleShowVersion; ) // --- open methods for accessing data window.model = _obj; // open access to the local object ))(); //--- model //+++ presentation (function ()( var _lay = app.CreateLayout("linear", "VCenter,FillXY"); var _btnShowVersion = app.CreateButton(window.model.btnGetTitle(), 0.3, 0.1); _btnShowVersion.name = "_btnShowVersion"; _btnShowVersion.SetBackColor("#66778976"); dLayout(_lay);

))(); //--- presentation //+++ controller (function(p_object)( var _obj = ; // public object search method _obj.findObjectById = function(p_name)( var _objectList = app.GetObjects(); for (var _i in _objectList)( if(_objectList[_i].name == p_name)( return _objectList[ _i]; ) ) return null; window.control = _obj))(); function OnStart())( var _buttonShowVersion = window.control.findObjectById("_btnShowVersion"); //+++ action _buttonShowVersion.SetOnTouch(function())( this.SetText(window.model.getVersion()); )); / / --- action ) //--- controller

Due to the separation of functions, the application code has increased several times.

Initially, all variables are made private and only at the end, if necessary, access to them is made via global object window, which allows you to do without global variables.

The example implements a widget search, as in Java, but you can do it simpler and make the code more efficient by opening access to the object through the global associative array:

Window.controls = ;
window.controls.buttonShowVersion = _btnShowVersion;

The data, its display and reaction to actions are located in different blocks, without mixing with each other, which allows the developer to work with them easier. The easier it is to work with data and code, the fewer errors there will be, the easier it will be to debug, support and scale.

It is not necessary to separate all these three components from each other. There are several variations of MVC, as well as incomplete implementations of this model. For example, you can separate the data and combine the action code with the controls using anonymous functions callback.

When working in an object-oriented environment, the separation of code and data is already present initially: data and actions are grouped in classes, objects interact with each other through open methods etc. MVC allows for a finer, more explicit separation of code and data into their core functions.

To better understand the benefits of using the MVC model, let's look at dividing the code into separate files.

Three-file implementation of the MVC model

Code division by different files used for more comfortable work with him. Great amount The small files you see in MVC projects may call this statement into question, but seeing the files is one thing, working with them is another. At each moment of time, the developer interacts with one file from some small set of them. To do this, you need to have a good understanding of the project organization structure and constantly monitor three files- model, view and controller, so as not to accidentally edit third-party code. Due to limitations of the DroidScript editor, such grouping is only possible by file names in the root directory, for example:

myproject_model.js - model
myproject_view.js - view
myproject_control.js - controller

Below is an example of dividing the code of the previous example into files.

myproject_model.js - model(function())( var _obj = ; //+++ data var _version = "Application version 1.0"; //--- data //+++ string resource var _titleShowVersion = "Show version"; //+++ string resource _obj.getVersion = function() ( return _version; ) _obj.btnGetTitle = function() ( return _titleShowVersion; ) window.model = _obj ))(); myproject_view.js - view(function ()( var _lay = app.CreateLayout("linear", "VCenter,FillXY"); var _btnShowVersion = app.CreateButton(window.model.btnGetTitle(), 0.3, 0.1); _btnShowVersion.name = "_btnShowVersion" ; _btnShowVersion.SetBackColor("#66778976"); _btnShowVersion.SetMargins(0, 0.05, 0, 0); _lay.AddChild(_btnShowVersion(_lay)); myproject_control.js - controller app.LoadScript("myproject_model.js"); app.LoadScript("myproject_view.js");(function(p_object)( var _obj = ; // object search method _obj.findObjectById = function(p_name)( var _objectList = app.GetObjects(); for (var _i in _objectList)( if(_objectList[_i].name = = p_name)( return _objectList[ _i]; ) ) return null; window.control = _obj; function OnStart())( var _buttonShowVersion = window.control.findObjectById("_btnShowVersion"); //+++ action _buttonShowVersion.SetOnTouch(function())( this.SetText(window.model.getVersion()); )); / / --- action )

This simple division of code into files was not easy. To do this, a connection with the model was established in advance through the public property of the global root object - window.model, and the connection with the view is through a global array _map through the method app.GetObjects.

The advantage of dividing the code into files is that you can now replace the code as a whole block, for example, for quick launch implement the project simple model, and then replace the file with another more functional one, but with the same name and interface. This approach is used, for example, when repairing equipment. If earlier repairs consisted of a slow and painstaking search and replacement of failed radio components, now standard units are being replaced. The cost of repairing a complex board is significantly higher than its quick replacement.

It follows from the above that a well-designed interface can significantly simplify the subsequent integration of modules.

IN JavaScript objects are passed by reference. Changing the widget properties in the controller will change the properties himself widget. Theoretically, it is possible to separate view objects from code objects, as is done in Java, where xml structures are used as the first, but there is little point in this for two reasons - absence in DroidScript visual editor interface and a limited set of available properties of API objects.

Multi-file implementation of the MVC model

Depending on the tasks assigned and the complexity of the project, the details of the separation of code and data, in general, can be different. You can further separate user data from resources, you can drill down into resources by type, group actions, etc. But the DroidScript editor does not allow you to work fully functionally using MVC.

MVC concept(Model-View-Controller: model-view-controller) has been mentioned very often in the world of web programming in recent years. Everyone who is in any way connected with web application development has come across this acronym in one way or another. Today we will understand what the MVC concept is and why it became popular.

Ancient history

MVC is not a project pattern, it is a design pattern that describes how to build the structure of our application, the responsibilities and interaction of each of the parts in this structure.

It was first described in 1979, of course, for a different environment. There was no concept of a web application back then. Tim Berners Lee sowed the seeds of World Wide Web(WWW) in the early nineties and changed the world forever. The template we use today is an adaptation of the original template for web development.

The wild popularity of this structure in web applications was due to its inclusion in two development environments that became very popular: Struts and Ruby on Rails. These two development environments set the path for hundreds of development environments that were created later.

MVC for web applications

The idea behind the MVC design pattern is very simple: we need to clearly separate responsibilities for the various functioning in our applications:

The application is divided into three main components, each of which is responsible for various tasks. Let's look at the components in detail using an example.

Controller

Controller manages user requests (received as HTTP GET or POST requests when the user clicks on interface elements to perform various actions). Its main function is to call and coordinate the action of the necessary resources and objects needed to perform actions specified by the user. Typically the controller calls the appropriate model for the task and selects suitable look.

Model

Model- These are the data and rules that are used to work with the data that represent the concept of managing the application. In any application, the entire structure is modeled as data that is processed in a certain way. What is a user for an application - a message or a book? Only data that must be processed according to rules (date cannot point into the future, email must be in a certain format, name cannot be longer than X characters, and so on).

The model gives the controller a representation of the data that the user has requested (message, book page, photo album, etc.). The data model will be the same no matter how we want to present it to the user. Therefore we choose any accessible view to display data.

The model contains the most important part of the logic of our application, the logic that solves the problem we are dealing with (forum, store, bank, etc.). The controller contains basically the organizational logic for the application itself (much like housekeeping).

View

View provides various ways representations of data that are obtained from the model. It can be a template that is filled with data. There may be several different types, and the controller chooses which one is suitable the best way for the current situation.

A web application typically consists of a set of controllers, models, and views. The controller can be designed as a main controller that receives all requests and calls other controllers to perform actions depending on the situation.

Let's look at an example

Let's say we need to develop an online bookstore. The user can perform the following actions: view books, register, buy, add items to current order, create or delete books (if he is an administrator). Let's see what happens when a user clicks on a category fantasy to view the titles of books that are available in our store.

We have a specific controller to handle all actions related to books (view, edit, create, etc.). Let's call it books_controller.php in our example. Also we need a model like book_model.php, which processes the data and logic associated with a store item. In conclusion, we need several views to represent the data, such as a book list, an edit page, and so on.

The following figure shows how a user's request to view a list of books on a topic is processed fantasy:

The controller (books_controller.php) receives the user request (HTTP GET or POST request). We can create a central controller, for example index.php, which receives the request and calls books_controller.php.

The controller checks the request and parameters and then calls the model(book_model.php), asking she has a list of available books on the topic fantasy .

The model receives data from the database (or another source that stores information), applies filters and the necessary logic, and then returns data that represents a list of books.

The controller uses the appropriate view to present data to the user. If the request comes from a mobile phone, the mobile phone view is used; if the user uses a certain interface design, then the corresponding view is selected, and so on.

What are the advantages?

The most obvious benefit we get from using the MVC concept is the clear separation of presentation logic (user interface) and application logic.

Support for different types of users who use different types of devices is common problem our days. The interface provided should be different if the request comes with personal computer or from a mobile phone. The model returns the same data, the only difference is that the controller selects different kinds to output data.

In addition to isolating views from application logic, the MVC concept significantly reduces complexity large applications. The code is much more structured, making it easier to maintain, test, and reuse solutions.

Why use the work environment?

When you use the workbench, the basic MVC structure is already prepared and all you have to do is expand the structure by placing your files in the appropriate directories to match the MVC pattern. Plus, you'll have a set of features that are already written and well tested.

Let's take cakePHP as an example working environment MVC. After installation you will have three main directories:

• cake/
• vendors/

Folder app is where your files are located. This is the place to develop your part of the application.

In folder cake cakePHP files (workbench functionality) are hosted.

Folder vendors serves for storage PHP libraries third party developers.

Yours working space(app directory) has the following structure:

• app/
  • config/
  • controllers/
  • locale/
  • models/
  • plugins/
  • tests/
  • vendors/
  • views/
  • webroot/

You need to place your controllers in a directory controllers, models in the directory models and types in the directory views!

Once you start using the production environment, it will immediately become clear where almost every part of your application that needs to be created or modified resides. This organization in itself greatly simplifies the process of developing and maintaining an application.

Using the workbench for our example

Because this lesson is not intended to show the process of creating an application using cakePHP, we will only show the code for the model, controller and view with comments about the benefits of using the MVC workbench. The code is deliberately simplified and unsuitable for use in a real application.

Remember, we were looking at a bookstore and a curious user who wanted to see full list books on the topic fantasy. The controller received the user's request and coordinated the necessary actions.

So, as soon as the user clicks the button, the browser requests the given url:

www.ourstore.com/books/list/fantasy

CakePHP formats URL using a pattern /controller/action/param1/param2, Where action is a function that is called by the controller. In the old classic form, the url will look like this:

www.ourstore.com/books_controller.php?action=list&category=fantasy

Controller

In the cakePHP working environment, our controller will look like this:

class BooksController extends AppController (

Function list($category) (

$this->set("books", $this->Book->findAllByCategory($category));

Function add() ( ... ... )

Function delete() ( ... ... )

... ... } ?>

Simple, isn't it? This controller will be saved as books_controller.php and posted in /app/controllers. It contains a list of functions that perform the actions for our example, as well as other functions for performing book-related operations (add a new book, delete a book, and so on).

The work environment provides us with many ready-made solutions and you just need to create a list of books. There is a base class that already defines the basic functionality of the controller, so you need to inherit the properties and functions of this class ( AppController is the heir Controller).

All you have to do in the action list is call the model to get the data and then select a view to present it to the user. Here's how it's done.

this->Book- this is our model, and part of the code:

$this->Book->findAllByCategory($category)

tells the model to return a list of books on the selected topic (we'll look at the model later).

Method set in line:

$this->set("books", $this->Book->findAllByCategory($category));

The controller passes data to the view. Variable books accepts the data returned by the model and makes it available to the view.

Now all that remains is to display the view, but this function is done automatically in cakePHP if we use the default view. If we want to use a different type, we must explicitly call the method render.

Model

The model is even simpler:

class Book extends AppModel (

Why is it empty? Because it inherits from a base class that provides the required functionality and we need to use CakePHP's naming convention to have the runtime handle all other tasks automatically. For example, cakePHP knows based on the name that this model used in BooksController, and that it has access to a database table named books.

With this definition, we will have a model that can only read, delete, or store data in the database.

Save the code as book.php in folder /app/models.

View

All we need to do now is create a view (by at least, one) for a list of actions. The view will have HTML code and a few (as few as possible) lines of PHP code to loop through the array of books that the model provides.

Name	Author	Price

As you can see, the view does not create a full page, but only a fragment of HTML (a table in in this case). Because CakePHP provides another way to define the page template, and the view is inserted into this template. The workbench also provides us with some helper objects to perform common tasks while creating parts of the HTML page (inserting forms, links, Ajax or JavaScript).

Save the view as list.ctp(list is the action name and ctp means CakePHP template) in the folder /app/views/books(because it's a view for a controller action).

This is how all three components are executed using the CakePHP workbench!

Model-View-Controller (MVC, “Model-View-Controller”, “Model-View-Controller”) - a scheme for dividing application data, user interface and control logic into three individual components: model, view and controller - in such a way that modification of each component can be carried out independently.

Encyclopedic YouTube

• 1 / 5

  The MVC concept was described by Trygve Reenskaug in 1978, who worked at the Xerox PARC research center on the Smalltalk programming language. Later, Steve Burbeck implemented the pattern in Smalltalk-80.

  Subsequently, the design pattern began to evolve. For example, a hierarchical version of HMVC was introduced; MVA, MVVM.

  After implementation by the company Apple technology WebObjects, implemented in Objective-C, began to popularize the pattern on the web [ ] .

  When WebObjects was ported to Java, the pattern became popular there too. More recent frameworks like Spring (October 2002) still have MVC implementation [ ] .

  A further round of popularity was brought by the development of frameworks focused on fast deployment, on Python languages and Ruby, Django and Rails, respectively [ ] . As of 2017, frameworks with MVC took a prominent position in relation to other frameworks without this pattern.

  Differences in template concept description

  With the development of object-oriented programming and the concept of design patterns, a number of modifications of the MVC concept were created, which, when implemented by different authors, may differ from the original. For example, Erian Vermi in 2004 described an example of a generalized MVC.

  In the preface to Richard Pawson's dissertation Naked Objects, Trygve Reenskaug mentions his unpublished most earlier version MVC, according to which:

  • The model referred to the user's "mind";
  • By view we meant an editor that allows the user to view and update information;
  • The controller was a tool for linking views together and was used by the user to solve his problems.

  Purpose

  The main purpose of applying this concept is to separate the business logic ( models) from its visualization ( representation, kind). Due to this separation, the possibility of reusing code increases. This concept is most useful when the user needs to see the same data simultaneously in different contexts and/or from different perspectives. In particular, the following tasks are performed:

  1. To one models you can attach several species, without affecting the implementation models. For example, some data may be presented simultaneously as a spreadsheet, a histogram, and a pie chart;
  2. Without affecting the implementation species, you can change reactions to user actions (mouse clicking on a button, entering data) - to do this, just use another controller;
  3. A number of developers specialize in only one of the areas: either developing a graphical interface or developing business logic. Therefore, it is possible to ensure that programmers developing business logic ( models), will not be aware at all of what performance will be used.

  Concept

  The MVC concept allows you to separate the model, view and controller into three separate components:

  Model

  The model provides data and methods for working with them: queries to the database, checking for correctness. The model is independent of the view - does not know how to visualize the data - and the controller - has no points of interaction with the user - simply providing access to and manipulation of the data.

  The model is built in such a way as to respond to requests by changing its state, and notification of “observers” can be built in.

  A model, due to its independence from visual representation, can have several different representations for one “model”.

  Performance

  The view is responsible for fetching the required data from the model and sending it to the user. The view does not process user input [ ] .

  A view can influence the state of a model by telling the model about it.

  Controller

  The controller provides “communications” between the user and the system. Controls and directs data from the user to the system and vice versa. Uses a model and a view to implement the required action.

  Functionality and discrepancies

  Since MVC does not have a strict implementation, it can be implemented in different ways. There is no generally accepted definition of where business logic should be located. It can be located both in the controller and in the model. In the latter case, the model will contain all business objects with all data and functions.

  Some frameworks strictly define where the business logic should be located, others do not have such rules.

  It is also not specified where the verification of user input should be located. Simple Validation can even occur in a view, but they are more common in a controller or model.

  Internationalization and formatting of data also does not have clear location guidelines.

  Conditional modifications

  To implement the “Model-View-Controller” scheme, enough big number design templates (depending on the complexity architectural solution), the main ones being “observer”, “strategy”, “linker”:

  The most typical implementation is in which the view is separated from the model by establishing an interaction protocol between them using the “event apparatus” (notation "events" certain situations that arise during the execution of the program - and sending notifications about them to all those who have subscribed to receive): with each special change in internal data in the model (denoted as an “event”), it notifies those views that depend on it about it, who are subscribed to receive such an alert - and the view is updated. This is how the "observer" pattern is used;

  When processing the user's reaction, the view selects, depending on the reaction, the desired controller, which will provide one or another connection with the model. This is done using the "strategy" pattern, or can be modified using the "command" pattern instead;

  To enable uniform handling of subobjects of a complex hierarchical type, the “linker” template can be used. In addition, other design patterns can be used - for example, the “factory method”, which will allow you to set the default controller type for the corresponding view.

  Most common mistakes

  Novice programmers very often interpret the MVC architectural model as a passive MVC model: the model acts solely as a set of functions for accessing data, and the controller contains business logic. As a result, the model code is in fact a means of obtaining data from the DBMS, and the controller is a typical module filled with business logic (see “script” in web programming terminology). As a result of this understanding, MVC developers began to write code that Pádraic Brady (known in the Zend Framework community) characterized as “Fat Stupid Ugly Controllers”:

  The average TTUK received data from the database (using the database abstraction layer, pretending that it was a model) or manipulated, checked, recorded, and also passed data to the View. This approach has become very popular because using such controllers is similar to the classic practice of using a separate PHP file for each page of the application.

  But object-oriented programming uses an active MVC model, where the model is not only a collection of data access code and

  What is MVC?

  So, MVC is about user interface(UI). Not necessarily graphic voice control good too. Let's not forget that a program may not have a user interface, but may have software interface(API) or have none at all and still be useful.

  But if we have a user, then there must be a user interface. What is an interface? This is the contiguous boundary between two systems. In our case: on the one hand - the program, on the other - the user. Here they are.

  The program is completely abstract, any subject code. It can do something useful, and the user has needs that can be satisfied with the help of this program. Then pieces of logic appear that “know” how, using this program, to do directly what the user wants. The pieces are not subject-specific, subject-specific logic in the program. They are more relevant to the user with his specific needs, and are combinations of calls and calls to the program.

  Use cases

  As an example, imagine a terminal for trading on an exchange. The terminal user submits an application in which he indicates that he wants to buy 20 shares of the Svetly Put company at a price of 1,500 rubles per share. It also indicates that the application is valid for four hours, and from which of his accounts the money will be debited if the transaction is successful.

  A tangible number of attributes. Some time passes, and he realizes that he will not be able to buy at this price and is ready to raise the price to 1,550 rubles, leaving all other values. Then he selects this application, clicks the “edit” button, indicates new price, Yes. It's comfortable.

  But on the exchange you cannot change an order; in the subject area there is no such concept. An application can only be submitted and cancelled. To give the user the opportunity to change an order in one click, you need to remember the old values, remove the order, let them edit what they remembered, and place a new order. Such a combination. But for the user it looks like one simple action: changing the application. This is called a use case.

  Let's supplement our diagram with space for use cases.

  

  The user should also be given the opportunity to pull these use cases and get results. These can be buttons and other graphical input/output elements, gestures, speech recognition and synthesis. Any option for exchanging data and commands. Voila:

  

  The user pulls one of the use cases, which, in turn, manipulates the program. The program publishes the result or changes in its state.

  So where is MVC anyway?

  All that remains is to give familiar names to the resulting components.

  

  When the model publishes changes, it doesn't care for whom, it doesn't know anything about View. Instead of or together with View, there may be another subsystem on the other end.

  Now a few details.

  It was a classic version of MVC - Active Model. It also happens that the model does not notify about changes. Then the controller takes on this responsibility. He knows what manipulations he performs on the model, and, obviously, he knows what changes in the state of the model may follow. This is Passive Model.

  And one moment. The division of code into subject and non-subject is conditional and depends on how pedantically we want to model subject area. Sometimes it's rational decision- include some kind of use case in the model. Perhaps this will reduce the amount of code overall and simplify it.

  We thank our subscriber Stanislav Ilyichev for the material