Introduction to Working with a Database in ASP.NET Web Pages (Razor) Sites

Imagine a typical address book. For each entry in the address book (that is, for each person) you have several pieces of information such as first name, last name, address, email address, and phone number.

A typical way to picture data like this is as a table with rows and columns. In database terms, each row is often referred to as a record. Each column (sometimes referred to as fields) contains a value for each type of data: first name, last name, and so on.

For most database tables, the table has to have a column that contains a unique identifier, like a customer number, account number, etc. This is known as the table's primary key, and you use it to identify each row in the table. In the example, the ID column is the primary key for the address book.

With this basic understanding of databases, you're ready to learn how to create a simple database and perform operations such as adding, modifying, and deleting data.

Relational Databases

You can store data in lots of ways, including text files and spreadsheets. For most business uses, though, data is stored in a relational database.

This article doesn't go very deeply into databases. However, you might find it useful to understand a little about them. In a relational database, information is logically divided into separate tables. For example, a database for a school might contain separate tables for students and for class offerings. The database software (such as SQL Server) supports powerful commands that let you dynamically establish relationships between the tables. For example, you can use the relational database to establish a logical relationship between students and classes in order to create a schedule. Storing data in separate tables reduces the complexity of the table structure and reduces the need to keep redundant data in tables.

Creating a Database

This procedure shows you how to create a database named SmallBakery by using the SQL Server Compact Database design tool that's included in WebMatrix. Although you can create a database using code, it's more typical to create the database and database tables using a design tool like WebMatrix.

1. Start WebMatrix, and on the Quick Start page, click Site From Template.
2. Select Empty Site, and in the Site Name box enter "SmallBakery" and then click OK. The site is created and displayed in WebMatrix.
3. In the left pane, click the Databases workspace.
4. In the ribbon, click New Database. An empty database is created with the same name as your site.
5. In the left pane, expand the SmallBakery.sdf node and then click Tables.
6. In the ribbon, click New Table. WebMatrix opens the table designer.
7. Click in the Name column and enter "Id".
8. In the Data Type column, select int.
9. Set the Is Primary Key? and Is Identify? options to Yes. As the name suggests, Is Primary Key tells the database that this will be the table's primary key. Is Identity tells the database to automatically create an ID number for every new record and to assign it the next sequential number (starting at 1).
10. Click in the next row. The editor starts a new column definition.
11. For the Name value, enter "Name".
12. For Data Type, choose "nvarchar" and set the length to 50. The var part of nvarchar tells the database that the data for this column will be a string whose size might vary from record to record. (The n prefix represents national, indicating that the field can hold character data that represents any alphabet or writing system — that is, that the field holds Unicode data.)
13. Set the Allow Nulls option to No. This will enforce that the Name column is not left blank.
14. Using this same process, create a column named Description. Set Data Type to "nvarchar" and 50 for the length, and set Allow Nulls to false.
15. Create a column named Price. Set Data Type to "money" and set Allow Nulls to false.
16. In the box at the top, name the table "Product". When you're done, the definition will look like this:
17. Press Ctrl+S to save the table.

Adding Data to the Database

Now you can add some sample data to your database that you'll work with later in the article.

1. In the left pane, expand the SmallBakery.sdf node and then click Tables.
2. Right-click the Product table and then click Data.
3. In the edit pane, enter the following records:

Remember that you don't have to enter anything for the Id column. When you created the Id column, you set its Is Identity property to true, which causes it to automatically be filled in. When you're finished entering the data, the table designer will look like this:

Displaying Data from a Database

Once you've got a database with data in it, you can display the data in an ASP.NET web page. To select the table rows to display, you use a SQL statement, which is a command that you pass to the database.

1. In the left pane, click the Files workspace.
2. In the root of the website, create a new CSHTML page named ListProducts.cshtml.
3. Replace the existing markup with the following:

@ < var db = Database.Open("SmallBakery"); var selectQueryString = "SELECT * FROM Product ORDER BY Name"; >    table, th, td 
Small Bakery Products
 @foreach(var row in db.Query(selectQueryString)) <  >
 
 
Id
 
Product
 
Description
 
Price
 
 
 
@row.Id
 
@row.Name
 
@row.Description
 
@row.Price
 
 
   

In the first code block, you open the SmallBakery.sdf file (database) that you created earlier. The Database.Open method assumes that the .sdf file is in your website's App_Data folder. (Notice that you don't need to specify the .sdf extension — in fact, if you do, the Open method won't work.)

Note The App_Data folder is a special folder in ASP.NET that's used to store data files. For more information, see Connecting to a Database later in this article.

SELECT * FROM Product ORDER BY Name 

Structured Query Language (SQL)

SQL is a language that's used in most relational databases for managing data in a database. It includes commands that let you retrieve data and update it, and that let you create, modify, and manage database tables. SQL is different than a programming language (like the one you're using in WebMatrix) because with SQL, the idea is that you tell the database what you want, and it's the database's job to figure out how to get the data or perform the task. Here are examples of some SQL commands and what they do:

SELECT Id, Name, Price FROM Product WHERE Price > 10.00 ORDER BY Name

This fetches the Id, Name, and Price columns from records in the Product table if the value of Price is more than 10, and returns the results in alphabetical order based on the values of the Name column. This command will return a result set that contains the records that meet the criteria, or an empty set if no records match.

INSERT INTO Product (Name, Description, Price) VALUES ("Croissant", "A flaky delight", 1.99)

This inserts a new record into the Product table, setting the Name column to "Croissant", the Description column to "A flaky delight", and the price to 1.99.

DELETE FROM Product WHERE ExpirationDate < "01/01/2008"

This command deletes records in the Product table whose expiration date column is earlier than January 1, 2008. (This assumes that the Product table has such a column, of course.) The date is entered here in MM/DD/YYYY format, but it should be entered in the format that's used for your locale.

The Insert Into and Delete commands don't return result sets. Instead, they return a number that tells you how many records were affected by the command.

For some of these operations (like inserting and deleting records), the process that's requesting the operation has to have appropriate permissions in the database. This is why for production databases you often have to supply a username and password when you connect to the database.

There are dozens of SQL commands, but they all follow a pattern like this. You can use SQL commands to create database tables, count the number of records in a table, calculate prices, and perform many more operations.

Inserting Data in a Database

This section shows how to create a page that lets users add a new product to the Product database table. After a new product record is inserted, the page displays the updated table using the ListProducts.cshtml page that you created in the previous section.

The page includes validation to make sure that the data that the user enters is valid for the database. For example, code in the page makes sure that a value has been entered for all required columns.

1. In the website, create a new CSHTML file named InsertProducts.cshtml.
2. Replace the existing markup with the following:

@ < Validation.RequireField("Name", "Product name is required."); Validation.RequireField("Description", "Product description is required."); Validation.RequireField("Price", "Product price is required."); var db = Database.Open("SmallBakery"); var Name = Request.Form["Name"]; var Description = Request.Form["Description"]; var Price = Request.Form["Price"]; if (IsPost && Validation.IsValid()) < // Define the insert query. The values to assign to the // columns in the Product table are defined as parameters // with the VALUES keyword. if(ModelState.IsValid) < var insertQuery = "INSERT INTO Product (Name, Description, Price) " + "VALUES (@0, @1, @2)"; db.Execute(insertQuery, Name, Description, Price); // Display the page that lists products. Response.Redirect("~/ListProducts"); >> >    label fieldset legend .validation-summary-errors 
Add New Product
 @Html.ValidationSummary("Errors with your submission:") 
 
Add Product
 
Name: 
 
Description: 
 
Price: 
 
  
 
 
   

The body of the page contains an HTML form with three text boxes that let users enter a name, description, and price. When users click the Insert button, the code at the top of the page opens a connection to the SmallBakery.sdf database. You then get the values that the user has submitted by using the Request object and assign those values to local variables. To validate that the user entered a value for each required column, you register each element that you want to validate:

Validation.RequireField("Name", "Product name is required."); Validation.RequireField("Description", "Product description is required."); Validation.RequireField("Price", "Product price is required."); 

The Validation helper checks that there is a value in each of the fields that you've registered. You can test whether all the fields passed validation by checking Validation.IsValid() , which you typically do before you process the information you get from the user:

if (IsPost && Validation.IsValid()) < // Process information here >

(The && operator means AND — this test is If this is a form submission AND all the fields have passed validation.) If all the columns validated (none were empty), you go ahead and create a SQL statement to insert the data and then execute it as shown next:

var insertQuery = "INSERT INTO Product (Name, Description, Price) VALUES (@0, @1, @2)"; 

Note As a security precaution, always pass values to a SQL statement using parameters, as you see in the preceding example. This gives you a chance to validate the user's data, plus it helps protect against attempts to send malicious commands to your database (sometimes referred to as SQL injection attacks).

To execute the query, you use this statement, passing to it the variables that contain the values to substitute for the placeholders:

db.Execute(insertQuery, Name, Description, Price); 

After the Insert Into statement has executed, you send the user to the page that lists the products using this line:

Response.Redirect("~/ListProducts"); 

If validation didn't succeed, you skip the insert. Instead, you have a helper in the page that can display the accumulated error messages (if any):

@Html.ValidationSummary("Errors with your submission:") 

Testing the Insert Page

1. View the page in a browser. The page displays a form that's similar to the one that's shown in the following illustration.
2. Enter values for all the columns, but make sure that you leave the Price column blank.
3. Click Insert. The page displays an error message, as shown in the following illustration. (No new record is created.)
4. Fill the form out completely, and then click Insert. This time, the ListProducts.cshtml page is displayed and shows the new record.

Updating Data in a Database

After data has been entered into a table, you might need to update it. This procedure shows you how to create two pages that are similar to the ones you created for data insertion earlier. The first page displays products and lets users select one to change. The second page lets the users actually make the edits and save them.

Important In a production website, you typically restrict who's allowed to make changes to the data. For information about how to set up membership and about ways to authorize users to perform tasks on the site, see Adding Security and Membership to an ASP.NET Web Pages Site.

1. In the website, create a new CSHTML file named EditProducts.cshtml.
2. Replace the existing markup in the file with the following:

@ < var db = Database.Open("SmallBakery"); var selectQueryString = "SELECT * FROM Product ORDER BY Name"; >    table, th, td 
Edit Small Bakery Products
 @foreach (var row in db.Query(selectQueryString)) <  >
 
 
 
 
Name
 
Description
 
Price
 
 
 
Edit
 
@row.Name
 
@row.Description
 
@row.Price
 
 
   

The only difference between this page and the ListProducts.cshtml page from earlier is that the HTML table in this page includes an extra column that displays an Edit link. When you click this link, it takes you to the UpdateProducts.cshtml page (which you'll create next) where you can edit the selected record. Look at the code that creates the Edit link:

Edit Edit Edit 

Notice that the href attribute is set to UpdateProducts/n , where n is a product number. When a user clicks one of these links, the resulting URL will look something like this: http://localhost:18816/UpdateProducts/6 In other words, the product number to be edited will be passed in the URL.

@ < Validation.RequireField("Name", "Product name is required."); Validation.RequireField("Description", "Product description is required."); Validation.RequireField("Price", "Product price is required."); var Name = ""; var Description = ""; var Price = Decimal.Zero; var ProductId = UrlData[0]; if (ProductId.IsEmpty()) < Response.Redirect("~/EditProducts"); >var db = Database.Open("SmallBakery"); if (IsPost && Validation.IsValid()) < var updateQueryString = "UPDATE Product SET Name=@0, Description=@1, Price=@2 WHERE ; Name = Request["Name"]; Description = Request["Description"]; Price = Request["Price"].AsDecimal(); db.Execute(updateQueryString, Name, Description, Price, ProductId); Response.Redirect(@Href("~/EditProducts")); >else < var selectQueryString = "SELECT * FROM Product WHERE var row = db.QuerySingle(selectQueryString, ProductId); Name = row.Name; Description = row.Description; Price = row.Price; >>    label < float: left; width: 8em; text-align: right; margin-right: 0.5em;>fieldset < padding: 1em; border: 1px solid; width: 35em;>legend < padding: 2px 4px; border: 1px solid; font-weight: bold;>.validation-summary-errors 
Update Product
 @Html.ValidationSummary("Errors with your submission:") 
 
Update Product
 
Name: 
 
Description: 
 
Price: 
 
  
 
 
   

SELECT * FROM Product WHERE 

var ProductId = UrlData[0]; 

var row = db.QuerySingle(selectQueryString, ProductId); 

var Name = row.Name; var Description = row.Description; var Price = row.Price; 

UPDATE Product SET Name=@0, Description=@1, Price=@2, WHERE 

db.Execute(updateQueryString, Name, Description, Price, ProductId); 

Response.Redirect(@Href("~/EditProducts")); 

Deleting Data in a Database

This section shows how to let users delete a product from the Product database table. The example consists of two pages. In the first page, users select a record to delete. The record to be deleted is then displayed in a second page that lets them confirm that they want to delete the record.

Important In a production website, you typically restrict who's allowed to make changes to the data. For information about how to set up membership and about ways to authorize user to perform tasks on the site, see Adding Security and Membership to an ASP.NET Web Pages Site.

1. In the website, create a new CSHTML file named ListProductsForDelete.cshtml.
2. Replace the existing markup with the following:

@ < var db = Database.Open("SmallBakery"); var selectQueryString = "SELECT * FROM Product ORDER BY Name"; >    table, th, td 
Delete a Product
 
 @foreach (var row in db.Query(selectQueryString)) <  >
 
 
 
 
Name
 
Description
 
Price
 
 
 
Delete
 
@row.Name
 
@row.Description
 
@row.Price
 
 
 
   

This page is similar to the EditProducts.cshtml page from earlier. However, instead of displaying an Edit link for each product, it displays a Delete link. The Delete link is created using the following embedded code in the markup:

@ < var db = Database.Open("SmallBakery"); var ProductId = UrlData[0]; if (ProductId.IsEmpty()) < Response.Redirect("~/ListProductsForDelete"); >var prod = db.QuerySingle("SELECT * FROM PRODUCT WHERE ProductId); if( IsPost && !ProductId.IsEmpty()) < var deleteQueryString = "DELETE FROM Product WHERE db.Execute(deleteQueryString, ProductId); Response.Redirect("~/ListProductsForDelete"); >>     
Delete Product - Confirmation
 
Are you sure you want to delete the following product?
 
Name: @prod.Name 
Description: @prod.Description 
Price: @prod.Price
 
   

This page is called by ListProductsForDelete.cshtml and lets users confirm that they want to delete a product. To list the product to be deleted, you get the ID of the product to delete from the URL using the following code:

var ProductId = UrlData[0]; 

The page then asks the user to click a button to actually delete the record. This is an important security measure: when you perform sensitive operations in your website like updating or deleting data, these operations should always be done using a POST operation, not a GET operation. If your site is set up so that a delete operation can be performed using a GET operation, anyone can pass a URL like http:///DeleteProduct/4 and delete anything they want from your database. By adding the confirmation and coding the page so that the deletion can be performed only by using a POST, you add a measure of security to your site. The actual delete operation is performed using the following code, which first confirms that this is a post operation and that the ID isn't empty:

if( IsPost && !ProductId.IsEmpty()) < var deleteQueryString = "DELETE FROM Product WHERE db.Execute(deleteQueryString, ProductId); Response.Redirect("~/ListProductsForDelete"); >

The code runs a SQL statement that deletes the specified record and then redirects the user back to the listing page.

Connecting to a Database

You can connect to a database in two ways. The first is to use the Database.Open method and to specify the name of the database file (less the .sdf extension):

var db = Database.Open("SmallBakery");

The Open method assumes that the .sdf file is in the website's App_Data folder. This folder is designed specifically for holding data. For example, it has appropriate permissions to allow the website to read and write data, and as a security measure, WebMatrix does not allow access to files from this folder.

The second way is to use a connection string. A connection string contains information about how to connect to a database. This can include a file path, or it can include the name of a SQL Server database on a local or remote server, along with a user name and password to connect to that server. (If you keep data in a centrally managed version of SQL Server, such as on a hosting provider's site, you always use a connection string to specify the database connection information.)

In WebMatrix, connection strings are usually stored in an XML file named Web.config. As the name implies, you can use a Web.config file in the root of your website to store the site's configuration information, including any connection strings that your site might require. An example of a connection string in a Web.config file might look like the following. Note $CREDENTIAL_PLACEHOLDER$ is a placeholder for the password key/value pair:

In the example, the connection string points to a database in an instance of SQL Server that's running on a server somewhere (as opposed to a local .sdf file). You would need to substitute the appropriate names for myServer and myDatabase , and specify SQL Server login values for username and password . (The username and password values are not necessarily the same as your Windows credentials or as the values that your hosting provider has given you for logging in to their servers. Check with the administrator for the exact values you need.)

The Database.Open method is flexible, because it lets you pass either the name of a database .sdf file or the name of a connection string that's stored in the Web.config file. The following example shows how to connect to the database using the connection string illustrated in the previous example:

As noted, the Database.Open method lets you pass either a database name or a connection string, and it'll figure out which to use. This is very useful when you deploy (publish) your website. You can use an .sdf file in the App_Data folder when you're developing and testing your site. Then when you move your site to a production server, you can use a connection string in the Web.config file that has the same name as your .sdf file but that points to the hosting provider's database — all without having to change your code.

Finally, if you want to work directly with a connection string, you can call the Database.OpenConnectionString method and pass it the actual connection string instead of just the name of one in the Web.config file. This might be useful in situations where for some reason you don't have access to the connection string (or values in it, such as the .sdf file name) until the page is running. However, for most scenarios, you can use Database.Open as described in this article.

Additional Resources

• SQL Server Compact
• Connecting to a SQL Server or MySQL Database in WebMatrix
• Validating User Input in ASP.NET Web Pages Sites