3.Inserting Data to Database using LINQ to SQL

STEP 1: Creating a new Website in Visual Studio

To get started then lets go ahead and fire up Visual Studio 2008 and create a new WebSite by selecting File > New WebSite.

STEP 2: Adding a DBML file

Since we are going to use L2S then we need to add .dbml file. To do this, just right click on the application root and select Add New Item. On the template select LINQ to SQL Classes file. See below screen shot:

 

Now rename your dbml file the way you want it and then click OK. Note that I’m using the Northwind database for this demo and on that case I renamed the dbml file to Northwind to make it friendlier.

Now open up server explorer in Visual Studio and browse the database that you wan’t to work on (in this case the Northwind database). Just for the purpose of this example I’m going to use the Customers table from the northwind database and drag it to the Northwind.dbml design surface. See the screen shot below:

 

That’s simple! Isn’t it?

What happens there is that by time you drag a table in the design surface, L2S will automatically generates the Business object for you within the DataContext and let you query against it.The DataContext is the main gateway by which you retrieve objects from the database and resubmit changes. You use it in the same way that you would use an ADO.NET Connection. In fact, the DataContext is initialized with a connection or connection string you supply. The purpose of the DataContext is to translate your requests for objects into SQL queries made against the database and then assemble objects out of the results. The DataContext enables language-integrated query by implementing the same operator pattern as the standard query operators such as Where and Select

STEP 3: Setting up the GUI

Now let’s go ahead and create our form for data entry. For the simplicity of this demo, I just set up the form like below:

<html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server">     <title>Untitled Page</title>     <style type="text/css">         .style1{width: 400px;}         .style1 td {width:200px;}     </style> </head> <body>     <form id="form1" runat="server">     <asp:Literal ID="LiteralMessage" runat="server"></asp:Literal>     <table class="style1">         <tr>             <td>Company ID</td>             <td><asp:TextBox ID="TextBoxID" runat="server"/></td>         </tr>         <tr>             <td>Company Name</td>             <td><asp:TextBox ID="TextBoxCompanyName" runat="server"/></td>         </tr>         <tr>             <td>Contact Name</td>             <td><asp:TextBox ID="TextBoxContactName" runat="server"/></td>         </tr>         <tr>             <td>Contact Title</td>             <td><asp:TextBox ID="TextBoxContactTitle" runat="server"/></td>         </tr>         <tr>             <td>Address</td>             <td><asp:TextBox ID="TextBoxAddress" runat="server"/></td>         </tr>         <tr>             <td>City</td>             <td><asp:TextBox ID="TextBoxCity" runat="server"/></td>         </tr>         <tr>             <td>Region</td>             <td><asp:TextBox ID="TextBoxRegion" runat="server"/></td>         </tr>         <tr>             <td>Postal Code</td>             <td><asp:TextBox ID="TextBoxPostalCode" runat="server"/></td>         </tr>         <tr>             <td>Country</td>             <td><asp:TextBox ID="TextBoxCountry" runat="server"/></td>         </tr>     </table>     <asp:Button ID="Button1" runat="server" Text="Save" onclick="Button1_Click" />     </form> </body> </html>

STEP 4: Creating the SaveCustomerInfo() method

After setting up our GUI then let’s go ahead and create the method for inserting the data to the database using L2S. Here are the code blocks below:

using System; using System.Configuration; using System.Data; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.HtmlControls; using System.Web.UI.WebControls; using System.Xml.Linq; public partial class _Default : System.Web.UI.Page {     protected void Page_Load(object sender, EventArgs e)     {     }     protected void Button1_Click(object sender, EventArgs e)     {         SaveCustomerInfo();     }     private void SaveCustomerInfo()     {         using (NorthwindDataContext context = new NorthwindDataContext())         {             //Create a new instance of the Customer object             Customer cust = new Customer();             //Add new values to each fields             cust.CustomerID = TextBoxID.Text;             cust.CompanyName = TextBoxCompanyName.Text;             cust.ContactName = TextBoxContactName.Text;             cust.ContactTitle = TextBoxContactTitle.Text;             cust.Address = TextBoxAddress.Text;             cust.City = TextBoxCity.Text;             cust.Region = TextBoxRegion.Text;             cust.PostalCode = TextBoxPostalCode.Text;             cust.Country = TextBoxCountry.Text;             //Insert the new Customer object             context.Customers.InsertOnSubmit(cust);             //Sumbit changes to the database             context.SubmitChanges();             //Display Message for successful operation             LiteralMessage.Text = "<p style='color:Green;'>Information Successfully saved!</p>";         }     } }

As you can see, the code above was very straight forward. First we have created a new instance of the DataContext which we had created on STEP 2 and wrapped it inside the “using” block; this is to ensure that the DataContext will be disposed after its processing. Second we created a new instance of the Customer object that was defined within the DataContext, this object has properties which will be filled with values that comes from the user inputs. Third we inserted a new Customer object to the Customers set and then call the context.SubmitChanges to update our database. Lastly, L2S will do the rest for you ;).

Note: The Customer and Customers set objects are automatically created once you’ve added the Customer table in the .dmbl design surface.

STEP 5: Run the code

Running the code above will look something like below on the browser:

From there we can fill in those fields with values we want. Just for this demo, notice that I have filled in those fields with a sample data. Hitting the save button will invoke the method SaveCustomerInfo() which is responsible for doing the insert operation. Now if we look at the database we can see that the data we entered was successfully being saved to the database. See the screen shot below:

http://geekswithblogs.net/dotNETvinz/archive/2010/03/11/inserting-data-to-database-using-linq-to-sql.aspx

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2.Fetch Data From Database(Using LINQ to SQL)

STEP 1: Setting up the GUI

To get started, add a new WebForm to your application and set up the GUI. Again just for the simplicity of this demo,I just set up the GUI like this:

<html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server">     <title>LINQ to SQL Demo Part 2</title>     <style type="text/css">         .style1{width: 400px;}         .style1 td {width:200px;}     </style> </head> <body>     <form id="form1" runat="server">         <asp:DropDownList ID="DropDownListCustomerID" runat="server"             AutoPostBack="true"             onselectedindexchanged="DropDownListCustomerID_SelectedIndexChanged">         </asp:DropDownList>         <br />         <table class="style1">             <tr>                 <td>Company Name</td>                 <td><asp:TextBox ID="TextBoxCompanyName" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>Contact Name</td>                 <td><asp:TextBox ID="TextBoxContactName" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>Contact Title</td>                 <td><asp:TextBox ID="TextBoxContactTitle" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>Address</td>                 <td><asp:TextBox ID="TextBoxAddress" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>City</td>                 <td><asp:TextBox ID="TextBoxCity" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>Region</td>                 <td><asp:TextBox ID="TextBoxRegion" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>Postal Code</td>                 <td><asp:TextBox ID="TextBoxPostalCode" runat="server" ReadOnly="true"/></td>             </tr>             <tr>                 <td>Country</td>                 <td><asp:TextBox ID="TextBoxCountry" runat="server" ReadOnly="true"/></td>             </tr>         </table>     </form> </body> </html>

If you notice, I set the ReadOnly attribute of each TextBox to True; this is because we don’t need users to edit the fields in the form once the TextBox is filled with data.

STEP 2: Populating the DropDownList with the list of Customers.

Now on our code behind page let’s go ahead and create the method for fetching the list of customers. Here’s the code block below:

private List<Customer> GetCustomers(){         using (NorthwindDataContext context = new NorthwindDataContext()){             return (from c in context.Customers select c).ToList();         }     }

The code above is the LINQ syntax for querying data. It basically query the Customers object that is generated from the DataContext and then fetch the results. 

Since we are done creating the method for fetching the list of customers then we can simply call that method and populate the DropDownList with the results. Typically we do this at Page_Load event within Not IsPostBack block like below:

protected void Page_Load(object sender, EventArgs e)     {         if (!Page.IsPostBack) {             DropDownListCustomerID.DataSource = GetCustomers();             DropDownListCustomerID.DataTextField = "ContactName";             DropDownListCustomerID.DataValueField = "CustomerID";             DropDownListCustomerID.DataBind();         }     }

As you can see the code above is very straight forward and self explanatory. Running the code above will display something like below:

 

Let’s proceed and continue with the next Step.

STEP 3: Populating the form with Customer’s Information

The next step is we are going to populate the form with the customer information based on the CustomerID selected from the DropDownList.

Note: Since the form will be populated based on the selected item from the DropDownList then you’ll need to set up the AutoPostBack attribute to TRUE in the DropDownList so that the SelectedIndexChanged event will fire up.

Here’s the code block below for fetching the customer information based on customer ID:

private List<Customer> GetCustomerInfo(string customerID) {         using (NorthwindDataContext context = new NorthwindDataContext()){             return(from c in context.Customers                    where c.CustomerID == customerID                    select c).ToList();         }     }

The code above is the LINQ syntax for querying data. As you can see we created a new instance of the DataContext and query the Customers object based on the parameter we passed on the GetCustomerInfo() method. Once we invoke the LINQ ToList() function, this LINQ query will issue a parameterize SQL query to the database in which the SQL Server can understand and then bring back the results to the DataContext.

One of the cool things about L2S is we don’t need to worry about how the query is being constructed because L2S will take care of that for you including mapping of the data types from your table columns, mapping relationships between tables, etcetera, etcetera and etcetera. Always keep in mind that L2S is an ORM (Object Relational Mapper) and so we don’t need to deal directly with databases, tables and columns but instead we deal with the objects that is in the DataContext and query the data against it using LINQ syntax.

STEP 4: Populating the Forms with Data

The next step is to populate our form with data based on the selected value from the DropDownList. To do this, we can simply call the method GetCustomerInfo() at the SelectedIndexChanged event of DropDownList like below:

protected void DropDownListCustomerID_SelectedIndexChanged(object sender, EventArgs e) {         var customerInfo = GetCustomerInfo(DropDownListCustomerID.SelectedValue);         TextBoxCompanyName.Text = customerInfo[0].CompanyName;         TextBoxContactName.Text = customerInfo[0].ContactName;         TextBoxContactTitle.Text = customerInfo[0].ContactTitle;         TextBoxAddress.Text = customerInfo[0].Address;         TextBoxCity.Text = customerInfo[0].City;         TextBoxRegion.Text = customerInfo[0].Region;         TextBoxPostalCode.Text = customerInfo[0].PostalCode;         TextBoxCountry.Text = customerInfo[0].Country;     }

The code above calls the method GetCustomerInfo() and pass the selected value of the DropDownList as a parameter to that method. We then store it a customerInfo implicit typed variable and assign each TextBox with the corresponding data returned from the query.

When you run the code above and select an item in the DropDownList, you will see that the textbox fields will be populated with data based from what you have selected in the DropDownList.

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