tailieunhanh - Microsoft SQL Server 2005 Developer’s Guide- Part 21

Microsoft SQL Server 2005 Developer’s Guide- P21:SQL Server 2005 is a feature-rich release that provides a host of new tools and technologies for the database developer. This book is written to help database developers and DBAs become productive immediately with the new features and capabilities found in SQL Server 2005. | Chapter 6 Developing Database Applications with 179 DataView Figure 6-2 The DataSet architecture When changes are made to the data contained in a DataTable object the ColumnChanging ColumnChanged RowChanging and RowChanged events are fired. When data is deleted from a DataTable object the RowDeleting and RowDeleted events are fired. New rows are added to a DataTable by calling the DataTable s NewRow method and passing it a DataRow object. The maximum number of rows that can be stored in a DataTable is 16 777 216. The DataTable is also used as a basis to create DataView objects. DataColumn The DataColumn class is located in the .NET Framework at . The DataColumn class represents the schema of a column in a DataTable object. The DataColumn class contains several properties that are used to define the type of data contained in the DataColumn object. For example the DataType property controls the type of data that can be stored in the DataColumn object the DataValue property contains the DataColumn s value the AllowDBNull property specifies whether the DataColumn can contain NULL values the MaxLength property sets the maximum length of a Text DataType and the Table property specifies the DataTable object that 180 Microsoft SQL Server 2005 Developer s Guide the DataColumn belongs to. DataColumns can be made to contain unique values by associating a UniqueConstraint object with the DataColumn object. In addition you can relate a DataColumn object to another DataColumn object by creating a DataRelation object and adding it to the DataSet s DataRelationCollection. DataRow Found in the .NET Framework at the DataRow class represents a row of data in the DataTable object. The DataRow class and the DataColumn class represent the primary objects that make up the DataTable class. The DataRow object is used to insert update and delete rows from a DataTable. Rows can be added to a DataTable by either creating a new DataRow object .

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