Essential ADO.NET

5.10. DataSets and Nonrelational Data Types Revisited

In Chapter 4, you learned about using nonrelational data types, such as Object, with DataSet. There I note that DataColumn supports only a certain subset of data types. Object is not among them, although you can define and use a DataColumn of type Object (or Person) with only minor difficulties. In this chapter you've started using DataSet with nonrelational types by virtue of using SqlDataAdapter, which supports SQL Server's SQL_VARIANT type. The data type mappings in Appendix A map this data type to the CLR type Object.

The SQL_VARIANT data type was added to SQL Server to support the use of OLE DB providers such as the Exchange OLE DB Provider, which exposes heterogeneous hierarchies and ...