OleDbCommand and SqlCommand
When you call the Open method, you open a connection to the database. Now, you need to create a command to run against the database. You do this by creating an OleDbCommand object (or SqlCommand object if you are using a SqlConnection).
You have now established a connection to the database, and you have created a command to retrieve the records. As in ADO, 本文来自辣.文,论-文·网原文请找腾讯32491‘14 a couple of ways to access the records that result from a query. One is the DataSet you have already examined in some detail and will see again in a moment. This allows you to store the records in memory in a disconnected fashion。What if the amount of data you are retrieving is quite large and you don’t want to consume all that memory? ADO.NET provides another object, called the DataReader. The DataReader is just that: an object that reads the data. It reads the data one record at a time, in a forward-only, read-only stream. This allows you to examine one record at a time, and then move to the next. Only one record at a time is actually in memory, so this significantly cuts down on the memory required.
The DataSet
校园歌手大奖赛宣传资料The DataSet is the object you have been dealing with for some time. The DataSet actually contains one or more DataTable objects. A DataSet command can pull data from the database and store it in a DataTable inside a DataSet. Therefore, with ADO, a recordset is just what its name implies: a set of records. In ADO.NET, the DataSet acts as a collection for one or more data tables, and each data table may contain data from multiple tables in the underlying database. To create and fill a DataSet, you first must create a DataSetAdapter object and then set a reference back to the OleDbCommand or SqlCommand that will provide the records.
XML Integration
As you are aware, XML is currently “the big thing.” Everyone is talking about XML, even if they aren’t quite doing it yet. The idea behind XML is to provide a way to transfer structured or relational information in a text-only format. Beyond that, though, the data is self-describing and easy to manipulate into a different format.
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