Connecting an MVC application to a database Jim Warren, COMPSCI 280 S Enterprise Software Development

Today’s learning objectives  To be able to program the key components of a C#/.NET MVC application for  Establishing a database connection  Defining a data model for its tables  Querying the database  Presenting the user a view of the results  To gain familiarity with use of the MVC pattern and its application to a Web application in practice COMPSCI 2802

The Model-View-Controller approach  Last lecture we introduced the MVC pattern and instantiated a default Internet Application template for MVC in C#/.NET  Today we want to learn more about the MVC components and other supporting files of the application so we can integrate the application with our own database  The Model will define the database connection and map C# classes to the database tables  The View will be tailored to present information from a table  The Controller will execute database queries and return data as parameter to the View COMPSCI 2803 See

Getting MySQL and.NET to play together  Principles are the same regardless of the database solution  Get the infrastructure (DBMS and its tools)  Set up a database and get its server running  Establish interoperability of the database and the.NET environment .NET is proprietary to Microsoft, so they’d prefer you ran Microsoft SQL Server (‘Express’ version is included Visual Studio) rather than a competitor such as the free MySQL  Add to your program a ‘connection’  This specifies the running DBMS service, which database (set of tables, views etc.) you want and your ‘login’ as an authorised user on that database COMPSCI 2804

Specifics  Get MySQL running  I did this by installing XAMPP to get MYSQL, Apache, XAMPP Control Panel and PHPMyAdmin  Then just start Apache* and MySQL in XAMPP Control Panel  Used PHPMyAdmin to build an employee database with an employee table, and also to add a user “jim”  Establish interoperability of the technologies  Installed MySQL Connector Net  Did Project/Add Reference/Browse in VS to add the MySql.Web.dll and MySql.Data.dll from ConnectNet's Assemblies\v4.5 subdirectory * Apache only needed for PHPMyAdmin -.NET will use Internet Information Server (IIS) Express to serve the applications Web pages COMPSCI 2805

Add a connection  Go into Web.config (from Solution Explorer)  It’s an XML file with project metadata  There’s already a connection defined  It’s used for the user accounts that are built into this project by default  We’ll put in another ‘add’ COMPSCI 2806 The connection name will come up in the Model Part of that DLL we got from MySQL Connector Net The MySQL user we defined (and its password! – note you can encrypt part of configuration for security: us/library/ms254494(v=vs.110).aspx

Our Model: Employee.cs Handout 01COMPSCI using System.Data.Entity; using System.ComponentModel.DataAnnotations; using System.ComponentModel.DataAnnotations.Schema; namespace MvcLetsConnect.Models { public class EmployeesContext : DbContext { public EmployeesContext() : base("MySqlConnection") { } public DbSet Employees { get; set; } } [Table("employee")] public class Employee { [Key] public int IDnum { get; set; } public string Surname { get; set; } public string GivenNames { get; set; } public DateTime DateOfBirth { get; set; } } First ‘using’ directive is added for referencing the DbContext object; next two are for the ‘key’ and ‘table’ decorators Use that connection we added to the Web.config file Our context’s DbSet ‘Employees’ will be a collection of objects of type Employee The table in MySQL is named ‘employee’ Define properties of this class with names matched to table fields in MySQL ([Key] identifies IDnum as the primary key as set in MySQL) Entity Framework can create the table entity definitions graphically/automatically for SQL server, but still in beta for MySQL

Our Controller  The HomeController.cs file includes the handler for the index (home) page  Creating an instance of the Employees context initiates the database connection  Putting it in a ‘using’ statement is tidy – invokes the connection’s dispose method, which closes the connection when we’re done serving up the page  We can then invoke methods on the Employees collection such as to.Count() them or assign the whole collection as an enumerable list to be pointed to by an implicitly typed (‘var’) element that we pass to the View COMPSCI 2808 public ActionResult Index() { using (EmployeesContext db = new EmployeesContext()) { int j = db.Employees.Count(); ViewBag.j = String.Format("We have {0} records.",j); var data = db.Employees.ToList(); return View(data); } C# moment: the.Format method of the String class is handy for laying out output

Our View  Using the Index.cshtml file we display the data for the user on the home page COMPSCI ViewBag.Title = "People"; WebGrid grid = new WebGrid(Model); new [] { grid.Column("Surname","Last Name"), grid.Column("GivenNames","Given Names"), grid.Column("DateOfBirth","Date of Birth") }) keyword in Razor says that the data passed to the View will be interpreted as an enumerable list of Employee objects as defined in the Model section of the project Using C#-like syntax in a Razor code block we instantiate an instance of the WebGrid helper on the Model data Razor functions put the text of element ‘j’ of the ViewBag and the instance of a WebGrid into the body of the HTML. Each WebGrid Column is instantiated on an exact property name of the Employee class from the model

The result Handout 02COMPSCI 28010

The result: a closer look Handout 02COMPSCI In Chrome, if you right-click and select ‘Inspect Element’ it’ll open a window showing the HTML (bottom left) and the CSS styles that have been applied (bottom right)

A closer look (contd.)  The WebGrid and ViewBag aren’t there  Just as the C# code has been converted to CIL for the CLR, the View’s Razor syntax has been converted to HTML for the browser to consume  HTML moment: The tag defines the start of a table, with a to start each row and a (‘table data’) to start each cell  Note that Chrome’s Inspect Element navigation has opened the elements directly leading to the cell we inspected but, for instance, has the table header definition (‘thead’) closed Handout 02COMPSCI 28012

A closer look (contd. again)  If we inspect the ‘Given Names’ column header, we see that the WebGrid helper did even more for us  It built a hyperlink (HTML ‘a’ – for ‘anchor’ – tag) which sends back to the Controller a request for the page in a different sort order (and the Controller automatically knows how to handle this, too!)  Note how the Employee class property name (‘GivenNames’) is used in the URL  If we had had more rows, the WebGrid would’ve also built us links for paging the data Handout 02COMPSCI 28013

Making your mark with style  We can add a style parameter to the constructor for a grid.Column  In the Site.css file (under Content in the Solution Explorer) we can create a corresponding style definition to apply to any element of class surname  And the VS intelli-sense greatly assists writing the CSS code!  We can also change any HTML tag’s styling for the whole site by editing in Site.css  E.g. to make all the rows of any table amber (not depicted in next slide) Handout 02COMPSCI new [] { grid.Column("Surname","Last Name",style:"surname"),.surname { font-style: italic; width: 150px; } tr { background-color: #ffe030; }

Styling result Handout 02COMPSCI The class attribute of each body cell in the Last Name column has been given the value we specified Chrome has picked up to apply the style to the content (note how the Inspect Element tooltip [left] shows the cell as ‘td.surname’) n.b. You’ll probably need to hit Refresh on your browser to get the style change to show up

Another query syntax: LINQ  Language Integrated Query (LINQ)  Can modify our HomeController.cs to read:  Very similar to SQL, but actually part of.NET (i.e. integrated with the C# language)  Differs in leading with ‘from’ and ending with ‘select’ (a better order for the intelli-sense!)  Note that the class of the objects returned by the query (each row, the members pointed to by emp ) has to align to in the View definition Handout 02COMPSCI using (EmployeesContext db = new EmployeesContext()) { var emp = from e in db.Employees where e.DateOfBirth.Year < 1975 select e; return View(emp.ToList()); }

Where we’re up to  We’ve now been introduced to the MVC approach in C#/.NET  And we’ve seen how to connect it to a MySQL database  Now…  Work the first labsheet (if you haven’t already)  Look at Assignment 2 (if you haven’t already)  Make a start – use your break time wisely and don’t be afraid to read ahead into weeks 7 and 8  In weeks 7 and 8 we’ll extend what we can do with MVC in C#/.NET and get a firmer understanding of what we’ve used so far Handout 02COMPSCI 28017