Instructor s Notes Web Data Management The MVC Pattern. Web Data Management The MVC Pattern

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1 Web Data Management The MVC Pattern Quick Links & Text References Overview Pages Controller Pages Including Files Pages Case Include Files Pages Model Pages Views Pages MVC Pseudocode Pages Multiple Form Buttons Pages Additional Book Examples Overview MVC: Model-View-Controller The MVC pattern is an organizational scheme used for complex web sites, particularly if they need database access. Similar to the 3-tier model used in desktop programming MVC web site pages and libraries are divided into three components Models Contains the business logic and provide database access PHP libraries No HTML Murach creates a separate library file to support each table in the database We will implement these in Unit 5 Views The GUI components of the web site Mostly HTML with PHP code to display data Controller the index.php file (only one file) Uses an action variable to determine what data (model) is needed and which view to use to display that data Show and discuss animated MVC PowerPoint Page 1 of 13

2 When the user (via a browser) requests information from this site, the browser request is always sent to the index page. Note this is the only page visible to the browser The index page uses the action variable (a hidden form variable) to determine what data the user requested. If the page doesn t require any data (rare), the data access steps below are skipped The data request is sent to the appropriate model library (Unit 6) The model passes the data request to the database The database returns the appropriate data to the data model which in turn passes it back to the index file The index file then passes the data to the appropriate view, again based on the action variable. The view (mostly HTML) is inserted into the index page (via an include), the data is displayed in the appropriate locations (PHP) and the customized index page is returned to the browser as an HTTP response. Note that each time the user requests information from the site, the index page morphs to display the data the user requested. Page 2 of 13

3 The Controller The controller is the heart of the MVC pattern The controller contains the following main components Determination of the desired action Case statement to process the appropriate action Links to Case Include files Generally, there is a case for each view created by the web site Each case includes the following Extraction of form variables (optional) Validation of form variables (if appropriate) Often a call to a validation model function Calls to the appropriate model CRUD functions Often calls to multiple functions Include statement to import the appropriate HTML to morph the index page as appropriate The controller contains no HTML HTML is included from view files Examples on page 171 and 247 See pseudocode below Page 3 of 13

4 Including Files MVC view files are typically stored in the views folder and each view (basically a page) is stored in its own file. The cases used in the switch statement of the controller can also be stored in include files To include a file in the controller, use the PHP include statement include('views/errorpage.php'); include('views/employeecases.php'); This must be included where you want the HTML injected. Make a copy of the final Unit 2 example project and rename it Unit 3 Update the structure of the project folder to include: css images javascript model views Include files typically include PHP and HTML required to appropriately display the view (page) require( )can be used to include PHP libraries (don t include HTML) Unit 4 A third option doesn t really include another file, but tells the browser to request a different page Unit 6 A page can t include a fresh copy of itself. This technique effectively bypasses that limitation by telling the browser to load the page again, maybe with different parameters. header('location:.'); Very common usage. Tells browser to reload the default page of this site. The dot (.) represents the current folder. Since no page name is specified, the default page in that folder is loaded BIG IMPORTANT NOTE When including files from other folders, the path designated must be based on the controller. All files are included from index.php. Same thing for images. For example: header.php is stored in the views folder and probably includes an image that is stored in the images folder. When you designate the path to the image, assume you are bringing the image into the index.php page because ultimately, you will be. Page 4 of 13

5 BIG IMPORTANT NOTE Don t include blank lines at the beginning or end of include files. These can cause problems when you transfer PHP pages to an actual server. See PHP Journal Case Include Files As mentioned above, controllers include a switch statement that includes cases (multiple) for the actions of each table in the database Some of the cases actually include another switch statement (see below) with even more cases. Even with only two tables, the controller can become very cluttered by the switch statement and as you add more tables the switch statement almost becomes unmanageable. In this unit, there re only a few cases in the switch statement, but we ll be expanding that significantly in Unit 6 so we ll break out the cases right away. In order for this technique to work, we ll need a little strategy. Each action variable for a table starts with the table name E.g: employeelist, employeedetails, employeesave, triplist, tripdetails, tripsave, etc. Since they all start with the table name, we can tell the switch statement to include a separate file (of cases) for each table based on what the action variable starts with. switch (true) { case strpos($action,"employee")===0: include("model/employeecases.php"); case strpos($action,"trip")===0: include("model/tripcases.php"); //more cases for the other tables here default: echo "Unexpected action $action found.<br>"; }//end switch Page 5 of 13

6 Each case checks to see if the action variable starts with the table name for that case. Note the (triple) ===. If the action variable doesn t include the designated table name at all, strpos returns false. false is equivalent (double ==) to 0. We only want to include the cases when the action variable starts with the table name. Triple === solves the problem. Next, we need to create an include file of cases for each table (employeecases and tripcases in the example above) I refer to these as cases files (my technique, my term) Each cases file first starts out with the require statements needed for the table handled by the cases file. These require statements link in the model files described below. After the require statements comes another switch statement to handle the cases for this table. Turns out you can t enter an include statement under a switch, only case statements Since we want all the cases for one table to be together, we ll have put them in their own switch statement (which is included under one case in the controller). This case statement will need its own default case in case we receive an action that starts with the appropriate table name but isn t recognized. //Cases file for tblemployees require("model/employees.php"); //Other model files may be required as well switch($action) { case "employeedetails": //some processing here case "employeelist": //some processing here case "employeedelete": //some processing here default: echo "Unexpected action $action found.<br>"; }//end switch Page 6 of 13

7 This code would be stored in a file named employeecases.php I put the cases files in the model folder (they define how each table is handled), but you might consider creating a separate cases folder to hold the cases files Note that all the case values start with the table name Also note that the cases file also includes a default case Action may start with employee but still be unknown (won t be caught the controller switch default) The Model The business model of an MVC pattern web site is really a collection of PHP function libraries. Unit 4 and Unit 6 Murach creates a library for all the functions required to manage (CRUD) data for each table in the database. Depending on the needs of the application, there are typically separate functions to: retrieve the data in multiple ways (one function each) update a record delete a record add a record Other, non-database functions may also be included as needed by the business model Remove the weights calculations from results.php and place in model/weights.php Page 7 of 13

8 The Views The views of MVC pattern web sites are actually web pages They are not however directly accessible by the user Security benefit? Instead, they are included into the index page (controller) to define the latest appearance (morph) of that page. Most of these pages also require access to form variables and/or database result sets. The index page PHP sets up this information before the view is included. Like Visual Studio GUIs, views should not do any processing (calculations, data retrieval), they should only display the results in an appropriate format. To provide a consistent appearance of pages throughout the web site, Murach recommends defining standard headers and footers. Each is stored in a separate include file (.php file) Each is included at the beginning and end of the view file The header include file includes the following tags <!DOCTYPE html> <html lang="en"> <head></head> <title></title> <meta> <link> to css <body> <header></header> Includes a common title and/or logo, etc. The footer include file includes the following tags <footer></footer> Includes whatever you want on the bottom of all your pages </body> </html> Move the appropriate HTML from the index.php to the header.php file and store in the views folder. Note JavaScript imports do not go in header. Not all pages need them they go in the appropriate cases file Move the appropriate HTML from the index.php file to the footer.php file and store in the views folder. Page 8 of 13

9 Each of the view files (.php) includes the header file at the beginning and the footer file at the end This allows you to use different headers/footers for different views if necessary. The header is followed by another section <section id="main"> which allows formatting (css) of the non-header/footer component of the page The main section contains the HTML and PHP (snippets) required to display the page Most pages include a form tag with a hidden action variable. This variable is sent to the next iteration of the index form to designate which action it should take Note the action attribute of the form tag can simply be the empty string The form should also include a submit button to send the form variables (including action) to the next iteration of the index form. Alternatively, you can define simple links (<a> tags) that link back to the index page. These links MUST include a value for the action variable <a href="?action=showcustomers">show Customer List</a> This sample links back to the index page (note no file name is supplied) and sets the action variable appropriately Note the text after action= is not surrounded by quotes or apostrophes If you need to send more than one variable/value, separate the values with & Remove the remaining index page code and save as weightsedit.php in the view folder. Add include statements in weightsedit for the header and footer. Demo how to include a simple form to return to the data entry form. Include a link to return to the data entry form.?action=showcustomer&customerid=$avariable Page 9 of 13

10 MVC Pseudocode Controller pseudocode If $_REQUEST action is set $action = $_REQUEST action Else $action = default action Endif Code index.php 2 cases weightsedit weightsresults Select Case $action starts with employee Include employeecases.php Case $action starts with trip: Include tripcases.php (repeat above for all tables) Case else Display error End Select Page 10 of 13

11 Cases File Pseudocode Require model files needed for this table Select $action Case tablelist Generate list data Include list view Case tabledetails Get record details Get support data (combo box data) Include details view Case tablenew Details = "" Get support data (combo box data) Include details view Case tablesavenew Case tableupdate Select selected button Case btnsave Call Validation If no errors If tableupdate Call update function Else Call insert function End If Display list view Else details = REQUEST Get support data (combo box data) Include details view End If Case btncancel Display list view Case btndelete Call function to delete record Display list view End Select Case Else Display error End Select Page 11 of 13

12 View Pseudocode Include header section main Display using HTML Button or link (with action) to return to index End section Include footer Dealing With Multiple Form Buttons Some forms may include multiple buttons multiple submit buttons (see pseudocode above). Example: an edit form might include the standard submit button, but also a cancel button if the user wishes to leave the form without saving their changes Determining which button was clicked, is a piece of cake. In the controller, check the $_REQUEST array. Only one of the submit buttons can be clicked, so the $_REQUEST array will only have one button in it. Add Hidden action variable to weightsedit form to display weightsresults next Modify the action (.) MOVE results page to views. Rename weightsresults Update to include header and footer Test //See if btnsubmit was clicked if(isset($_request['btnsubmit'])) //do stuff else //if other button is set //do other stuff Note each button must be given a name in the form. Page 12 of 13

13 Additional Examples Murach includes numerous, complete MVC pattern web site examples. Most are little complicated at this stage of your MVC experience but will become more clear and more valuable in the next couple of units. Some of the code included in the model files may be foreign to you, but you should still be able to use the examples to develop your own MVC pattern sites Product Catalog: Pages Task List Manager: Pages (nice short example) Shopping Cart Application: Pages Product Manager (OOP): Pages Registration Application: Pages Guitar Shop (advanced): Pages Product Manager (advanced): Pages ecommerce Web Site (advanced): Pages Page 13 of 13