Datasheet

Displaying Data on the Web

ADO.NET Architecture

You now know that ADO.NET draws on a long history of data access. Almost inevitably, this means

that there is quite a lot to learn. Thankfully, Microsoft has put a great deal of thought into its new data

access technology, making it more logical and structured than previous attempts, while still providing a

wealth of features.

ADO.NET is made up of a collection of objects, some of which are entirely new, and others of which

have evolved from ADO. The main difference between these and their predecessors is that there is

now generally only one way to accomplish a task – ADO was a little infamous for providing several

means to exactly the same end!

The next few pages are concerned with taking a look at the main ADO.NET objects, and how they

cooperate to provide data manipulation. Laid out below is a diagram of the five main object types that

you'll be dealing with when you use ADO.NET:

Data Store

Connection

ConnectionString

Command

Connection

CommandText

CommandType

DataAdapter

SelectCommand

UpdateCommand

InsertCommand

DeleteCommand

DataSet

DataReader

If we work our way back from the database, taking the objects one by one, we can see how these objects

work together, and what functions they perform:

❑ The connection object is the route through which all instructions to (and results from) the data

store are sent. The user can specify which database to connect to, what authentication to use,

and so on.

❑ The command object contains the instructions that specify what information should be sent to

(or retrieved from) the database. It also contains a link to the connection that it's going to use.

❑ The data reader object provides a way of 'getting at' the information that's been retrieved by

the command object. The information is provided on a read-only basis – so it can't be edited –

and only one item of data is read at a time. Data readers provide an efficient (if inflexible) way

of processing large amounts of data; they are sometimes described as providing connected

access, since the connection with the database must remain open for as long as the data reader

is in use.