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)
ASP.NET 2.0 Interview Questions
24. While developing ASP.NET 2.0 web application you have a DataSet containing a Customer DataTable and an Order DataTable. You want to easily navigate from an Order DataRow to the Customer who placed the order. What object will allow you to easily navigate from the Order to the Customer? A. The DataColumn object B. The DataTable object C. The DataRow object D. The DataRelation object
25. Which of the following is a requirement when merging modified data into a DataSet? A. A primary key must be defined on the DataTable objects. B. The DataSet schemas must match in order to merge. C. The destination DataSet must be empty prior to merging. D. A DataSet must be merged into the same DataSet that created it.
26. You are working with a DataSet and want to be able to display data, sorted different ways. How do you do so? A. Use the Sort method on the DataTable object. B. Use the DataSet object’s Sort method. C. Use a DataView object for each sort. D. Create a DataTable for each sort, using the DataTable object’s Copy method, and then Sort the result.
27. Which of the following ways can you proactively clean up a database connection’s resources? A. Execute the DbConnection object’s Cleanup method. B. Execute the DbConnection object’s Close method. C. Assign Nothing (C# null) to the variable that references the DbConnection object. D. Create a using block for the DbConnection object.
29. What event can you subscribe to if you want to display information from SQL Print statements? A. InfoMessage B. MessageReceived C. PostedMessage D. NewInfo
30. To perform asynchronous data access, what must be added to the connection string? A. BeginExecute=true B. MultiThreaded=true C. MultipleActiveResultSets=trueD. Asynchronous=true
31. Which class can be used to create an XML document from scratch? A. XmlConvert B. XmlDocument C. XmlNew D. XmlSettings
32. Which class can be used to perform data type conversion between .NET data types and XML types? A. XmlType B. XmlCast C. XmlConvert D. XmlSettings
