Chapter 5. DataReaders
In the previous chapter, you learned to
execute simple nonquery commands to update the data source and
retrieve calculated values. You can also use queries to fetch a set
of rows from a data source in a single operation. In ADO.NET, there
are two ways to use query commands: with the disconnected
DataSet object, as discussed in later chapters,
and with the DataReader, which is the focus of
this chapter.
The DataReader is little more than a thin wrapper
over a cursor that retrieves query results in a read-only,
forward-only stream of information. The DataReader
won’t let you perform updates, see the results of
live updates, or move back and forth through a result set as a
server-side cursor does in traditional ADO programming. However, what
you sacrifice in flexibility, you gain in performance. Because this
cursor consumes few server resources and requires relatively little
locking, the DataReader is always a
performance-optimal way to
retrieve data.
In this chapter, you’ll learn how to use a
DataReader to retrieve data and schema
information, how to handle specialized data types such as binary
large objects (BLOBs), and how to write code that can access any type
of data source with the DataReader.
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