| A Multipart Series on ASP.NET 2.0's Data Source Controls |
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ASP.NET 2.0 introduced a number of new Web controls designed for accessing and modifying data.
These controls allow page developers to declaratively access and modify data without writing any
code to perform the data access. This article is one in a series of articles on ASP.NET 2.0's new data
source controls.
Data Source Control Basics - explores the concepts
and advantages of data source controls, and compares their usage in ASP.NET 2.0 to data access techniques in ASP.NET 1.x.
Accessing Database Data - shows how to use the
SqlDataSource and AccessDataSource controls to query data from a relational database.
Filtering Database Data with Parameters - learn how to
retrieve just a subset of database data based on hard-coded values and values from the querystring, other Web controls on the page,
session variables, and so on.
Retrieving XML Data with XmlDataSource Control - see how
to retrieve both remote and local XML data and display it in a data Web control.
Creating Custom Parameter Controls - learn how
to create your own custom, declarative Parameter controls for use in the data source controls' parameters collections.
Examining the Data Source Control's Events - explore the
events raised during a data source control's lifecycle.
Declaratively Caching Data - learn how to cache data
to the data cache simply by setting a couple of data source control properties.
Programmatically Accessing Data using the Data Source Controls -
programmatically retrieve, insert, delete, and update data using the SqlDataSource and AccessDataSource controls.
Inserting Data - learn how to insert data using
a SqlDataSource control. Also examines how to retrieve the IDENTITY column value for the just-inserted record.
Deleting Data - see how to delete data using
a SqlDataSource control. Also looks at how to programmatically cancel a delete.
Updating Basics - learn the basics of updating database data using a
SqlDataSource control. Also examines using the GridView to provide a web-based editing interface.
Customizing the Editing Interface - see how to
customize the GridView's columns to provide a customized editing interface that includes input validation and alternative
user interface elements.
Handling Database NULL Valuese - explore how to
extend the GridView's customized editing interface to handle database NULL values.
Using Optimistic Concurrency - see how to prevent
concurrent users from overwritting one anothers changes by using concurrency control.
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Because multiple users can visit the same web page concurrently, it is possible for a user visiting a data modification page to inadvertently overwrite
the modifications made by another user. Consider a page with an editable GridView. If two users visit this page simultaneously from different computers
and both edit the same row, whomever saves the first will have her changes overwritten by whomever saves the row last. This type of behavior is known as
"last write wins" and is the default behavior for web applications.
"Last write wins" is sufficient in applications where it is very rare for two users to be simultaneously working on the same data. If it is
commonplace for multiple users to be modifying the same set of data, you should consider implementing some form of concurrency control.
There are two flavors of concurrency control: optimistic and pessimistic. Optimistic assumes that concurrency violations are rare and that if such an error
occurs that it's adequate to ask one of the conflicting parties to re-enter their information. Pessimistic concurrency, on the other hand, implements
policies to ensure that concurrency violations cannot occur. These policies may add friction to the end user's data entry experience.
Microsoft offers a form of optimistic concurrency control from the SqlDataSource control that can be enabled by ticking a checkbox. This article looks
at different types of concurrency control and then shows how to implement the built-in optimistic concurrency control offered by the SqlDataSource control.
Read on to learn more!