Briefly introduce the MVC idea and the method of implementing MVC in PHP

The so-called MVC simply means classifying and layering the website source code.

The meaning of the three letters of MVC: M: Model model, responsible for database operations. V: View is responsible for calling the Model to retrieve data, and then calling the template to display the final effect. C: Controller, the entry point of the program, decides which View to call and tells the View what to do.

In this way, the execution order of the program is C-V-M or C-M, which is exactly the opposite of the name of MVC.

Why MVC?

1. It can make the physical structure of the website program more reasonable. When building a website with PHP, the stupidest way is to build each page into a PHP file. If your website only has three pages: index.php and menu.php.article.php, then you don’t need MVC. But when we make a general website, we often have dozens of pages. It is obviously not appropriate to put all the pages in the root directory. What we can accept, so you need a reasonable idea to classify your code, divide them into different directories according to functions, and intelligently load and call them by the program. This is what MVC will help you do.

2. Make the code easier to maintain. Let's look at a single page again. The stupidest way is to mix PHP code and HTML code. This is obviously not good enough. When maintaining the website, you have to distinguish between PHP and HTML. For a programmer, this is simply Only disaster. So many people use Smarty, so that they can separate "data processing" and "page display". This is really good, and many people are doing it, but this is not MVC. What MVC has to do is to separate "data processing" ” is further divided into “logical processing” and “database operations”, which is what is called layering. In this way, when your program has an error or you want to modify it, it becomes very easy. When the page displays an error, you can check V or the template file; when there is a problem with the logic, you can check C and V. ;When your database operation error occurs, check M. In fact, MVC generally divides a PHP page into 4 pages, namely C, V, M, and template. Each performs its own duties to facilitate management.

3. Conducive to code reuse. MVC will generally put a large function in a directory, which is managed by a C. For example, if we want to build a website with a membership system, we can put all the membership-related codes in the user directory and manage them uniformly by User_Controller. When another website of ours also needs a membership system, we can directly copy this directory. In the past, just modifying the interface was enough.

The idea of ​​implementing MVC in PHP

Three base classes are needed: Controller, View, and Model, and then different C, V, and M inherit them respectively to have corresponding properties and methods. If you don’t understand here, you can read an object-oriented book. To provide you with a design idea for the MVC base class, for reference only: 1. Design of Controller class A main() method, called by the program, mainly determines how to process it through the get and post variables. A getModel($model) method calls M in the corresponding directory when the database needs to be called. A display($view) method, called in the main() method, loads the corresponding V, and replaces the main() method of the corresponding V;

2.The design of View class is very similar to Controller A main() method, this method is called when C loads V so that the program can continue to execute. A getModel($model) method calls M in the corresponding directory when the database needs to be called. A display($template) calls the corresponding template file and passes the data to the template.

3. Design of Model class You can define some properties, such as which tables to operate, which fields to operate, etc. A getDB() method to obtain an instance of a database class (database classes are generally designed using the singleton mode) A load() method loads a data. An add() method can automatically construct SQL statements based on defined attributes and perform insertion operations. An eidt() method, same as above, but performs modification operations. A del() method, same as above, but performs a delete operation.

In order to enable novices to better understand the working principle of my idea, we now simulate a user login scenario to see how MVC works.

Now assume that all data is submitted to index.php,

Step one: We submit each get variable and tell index.php which C to use. For example, index.php can be like this? controller=user Then index receives the get variable, and does not need to do anything. It directly finds /user/controller.php and throws all the data to it. Originally GET and POST are global, so index.php does not need to do anything and directly calls C. The main function is enough, and the task of index.php is completed.

Step 2: The main function of C starts to execute, checks the variables, and finds the login operation that the user wants to perform (very simple, you just post the variable do=login), then calls getModel and loads the corresponding M class (for example, /user/models/ model.php), and instantiate it, call the load method of the instance, load the user's data, and determine whether it is consistent with the password submitted by the user. If the submitted data is incorrect, the header will jump to the error page. If it is correct, call display () method, load the corresponding V (such as /user/views/details.php), instantiate it, call its main() function, and enter the third step. At this point, the task of C has been completed, and the second operation is performed in the main function.

Step 3: You can choose to call getModel() to load M and rewrite the retrieved data, or you can pass the parameters (such as SESSION) when C instantiates V. After V has determined to get the data, display() and load Template, MVC execution is completed. Of course, due to word count and energy limitations, what is written here is only a very brief summary. There are many details to consider during actual implementation. But when I designed MVC, this was the general idea, and it has been used in practice, and it feels good.