Interview Tips Interview Tips, Interview Questions and Answers

Filtering Data in Web Forms Model Binding

To enable filtering, we’ll update our GetProducts() method to take a keyword parameter like below:

public IQueryable<Product> GetProducts([QueryString]string keyword)

{

    IQueryable<Product> query = db.Products;

 

    if (!String.IsNullOrWhiteSpace(keyword))

    {

        query = query.Where(p => p.ProductName.Contains(keyword));

    }

 

    return query;

}

If the keyword is empty or null, then the method returns all of the products in the database.  If a keyword is specified then we further filter the query results to only include those product’s whose names contain the keyword.

Understanding Value Providers

One of the things you might have noticed with the code above is the [QueryString] attribute that we’ve applied to the keyword method argument.  This instructs the Model Binding system to attempt to “bind” a value from the query string to this parameter at runtime, including doing any type conversion required.

These sources of user values are called “Value Providers”, and the parameter attributes used to instruct the Model Binding system which Value Provider to use are called “Value Provider Attributes”. The next version of Web Forms will ship with value providers and corresponding attributes for all the common sources of user input in a Web Forms application, e.g. query string, cookies, form values, controls, viewstate, session and profile. You can also write your own custom value providers.  The value providers you write can be authored to work in both Web Forms and MVC.

By default, the parameter name will be used as the key in the value provider collection, so in this case, a value will be looked for in the query string with the key “keyword”, e.g. ~/Products.aspx?keyword=chef. This can be easily overridden by passing the desired key in as an argument to the parameter attribute. In our example, we might like the user to be able to use the common “q” query string key for specifying the keyword:

public IQueryable<Product> GetProducts([QueryString("q")]string keyword)