Using Query String Parameters in ASP.NET

       4 minute read

Before reading…

  • Target Audience: This reference document targets developers with beginner to intermediate experience, whom are familiar with Microsoft .NET and web development.
  • Scenario: I provide an overview of query string parameters, how they’re used in ASP.NET, and a scenario that explains how to use them, including a code sample.
  • Sources: I wrote 100% of the content, including code samples, without an editor providing input. The information was obtained through my own experience, a few RFCs and Microsoft documentation on MSDN and TechNet.

…and here’s the sample.

When developing a web application, you often have scenarios that require input from users. Or you might need to pass information from one part of your application to another, such as between html pages or aspx web forms. Perhaps you need to process a name, address, product name, a combination of these things, or many others. Using a Query String parameter is a simple and efficient manner of communicating this information.

  1. Overview
  2. How to use them in ASP.NET
  3. Scenario
  4. Code sample
  5. Summary
  6. Further resources

Overview of query strings

The query string is part of the Uniform Resource Locator (URL) in the browser address field. Query string parameters are tagged on to the end of the URL address, following a question mark (?). The parameters consist of field-value pairs, which contain the attribute and its value. In the following example, the bold portion is the query string.

     http://www.yourcompany.com/products?product=widget

The key components to the query string are:

     ? – The question mark tells the web app to expect the string parameters

     Field – The attribute name, which usually describes the value it contains (product in the preceding example).

     Value – The value assigned to the field (widget in the preceding example)

Multiple parameters may be submitted by separating them with an ampersand (&), like so:

     http://www.yourcompany.com/products?product=widget&location=seattle

Here’s a sample using a search for “do you feel lucky” at Google.com:

     https://www.google.com/search?q=do%20you%20feel%20lucky

The ? tells Google to expect a query string; the q= provides the name of the field, and do%20you%20feel%20lucky is the value for the field.

Note:   %20 is the URL encoded value for a space character, as seen in the example of “do you feel lucky”

According to RFC 7230 Section 3.1.1 (Hypertext Transfer Protocol – HTTP/1.1), there is no limitation to how many characters can be used in an URL. Given that standard, there is no limit to the number of query strings that can be submitted. Realistically though, the different browsers and web servers impose practical limitations, not covered in this article.

How to use query strings in ASP.NET

Query strings are processed in Microsoft .NET using the QueryString Property of the HttpRequest Class. The QueryString Property is a NameValueCollection, which means that like an array, it can be referenced by the field name or position. For example:

     http://www.yourcompany.com/products?product=widget&location=seattle

The contents, or value, of the product field may be referenced either of these two ways:

  • By name: Request.QueryString[“product”]

  • By position (zero [0] based): Request.QueryString[0]

Scenario

Going a little further into how to use this with .NET, imagine that you want to use the values of product and location to see if a product is in stock at a specific warehouse. The user would select their product and preferred pickup location from drop-down lists on your web page. When they click submit, it would open a link to a URL, like the following.

     http://www.yourcompany.com/warehouse?product=widget&location=seattle

This URL takes them to a page called ‘warehouse,’ which will tell them if the product is available for pickup at that location. In your web application, the C# code behind ‘warehouse’ would have a method called CheckQueryStrings, as shown in the following code sample. The method reads the query strings and submits a request to the business layer of your app.

Code sample

1  private void CheckQueryStrings()
2  {
3      if (!Request.QueryString.Count.Equals(0))
4      {
5          string productName = Request.QueryString["product"];
6          string warehouseLocation = Request.QueryString["location"];
7          if (!string.IsNullOrEmpty(productName) && !string.IsNullOrEmpty(warehouseLocation))
8          {
9              CheckAvailability(productName, warehouseLocation);
10         }
11         else
12         {
13             MessageBox.Show("Please select a product and warehouse location.");
14         }
15     }
16 }

Line 3 – Verifies that query string parameters were submitted by checking the length of the collection.

Lines 5 & 6 – Create and populate string variables for the product and location query strings.

Line 7 – Before taking action on the query strings, verifies they are not null or empty.

Line 9 – The query strings contain characters, call the method CheckAvailability. Presumably, this method would live in the business layer of your application. It would handle the business logic of the request, calling into the data layer of your application to retrieve the results and process them.

Line 13 – The query strings do not contain characters, are null or empty, then show a dialog box to the user.

Summary

In this document, you’ve learned how to use query string parameters in ASP.NET with the following benefits.

  • The ability to use multiple query strings in a single URL, allows you to scale easily with the demands of your web application. Although, keep in mind that browsers and web servers have limitations in overall URL lengths.

  • Handling query string parameters in the C# code behind your ASP.NET pages is straightforward; allowing you to use the information throughout your web application.

As you can see, query string parameters are a simple and efficient method of communicating information throughout your web application.

Further resources

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