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Large UDTs in SQL Server 2008 (ADO.NET)

User-defined types (UDTs) introduced in SQL Server 2005 allow a developer to extend the server's scalar type system by storing common language runtime (CLR) objects in a SQL Server database. UDTs can contain multiple elements and can have behaviors, unlike the traditional alias data types, which consist of a single SQL Server system data type.

NoteNote

You must install the .NET Framework 3.5 SP1 (or later) to take advantage of the enhanced SqlClient support for large UDTs.

Previously, UDTs were restricted to a maximum size of 8 kilobytes. In SQL Server 2008, this restriction has been removed for UDTs that have a format of UserDefined.

For the complete documentation for user-defined types, see the version of SQL Server Books Online for the version of SQL Server you are using.

SQL Server 2005

SQL Server 2008

CLR User-Defined Types

CLR User-Defined Types

The GetSchema method of SqlConnection returns database schema information in a DataTable. For more information, see SQL Server Schema Collections (ADO.NET).

GetSchemaTable Column Values for UDTs

The GetSchemaTable method of a SqlDataReader returns a DataTable that describes column metadata. The following table describes the differences in the column metadata for large UDTs between SQL Server 2005 and SQL Server 2008.

SqlDataReader column

SQL Server 2005

SQL Server 2008

ColumnSize

Varies

Varies

NumericPrecision

255

255

NumericScale

255

255

DataType

Byte[]

UDT instance

ProviderSpecificDataType

SqlTypes.SqlBinary

UDT instance

ProviderType

21 (SqlDbType.VarBinary)

29 (SqlDbType.Udt)

NonVersionedProviderType

29 (SqlDbType.Udt)

29 (SqlDbType.Udt)

DataTypeName

SqlDbType.VarBinary

The three part name specified as Database.SchemaName.TypeName.

IsLong

Varies

Varies

The SqlDataReader has been extended in SQL Server 2008 to support retrieving large UDT values. How large UDT values are processed by a [SqlDataReader] depends on the version of SQL Server you are using, as well as on the Type System Version specified in the connection string. For more information, see the "Type System Version Changes" section in New Features in SQL Server 2008 (ADO.NET).

The following methods of SqlDataReader will return a SqlBinary instead of a UDT instance in earlier versions of SQL Server, or when the Type System Version does not specify SQL Server 2008:

The following methods will return an array of Byte[] instead of a UDT instance in earlier versions of SQL Server, or when the Type System Version does not specify SQL Server 2008:

Note that no conversions are made for the current version of ADO.NET.

The following SqlParameter properties have been extended to work with large UDTs.

SqlParameter Property

Description

Value

Gets or sets an object that represents the value of the parameter. The default is null. The property can be SqlBinary, Byte[], or a managed object.

SqlValue

Gets or sets an object that represents the value of the parameter. The default is null. The property can be SqlBinary, Byte[], or a managed object.

Size

Gets or sets the size of the parameter value to resolve. The default value is 0. The property can be an integer that represents the size of the parameter value. For large UDTs, it can be the actual size of the UDT, or -1 for unknown.

The following code fragment demonstrates how to retrieve large UDT data. The connectionString variable assumes a valid connection to a SQL Server database and the commandString variable assumes a valid SELECT statement with the primary key column listed first.

using (SqlConnection connection = new SqlConnection( 
    connectionString, commandString))
{
  connection.Open();
  SqlCommand command = new SqlCommand(commandString);
  SqlDataReader reader = command.ExecuteReader();
  while (reader.Read())
  {
    // Retrieve the value of the Primary Key column.
    int id = reader.GetInt32(0);
      
    // Retrieve the value of the UDT.
    LargeUDT udt = (LargeUDT)reader[1];

    // You can also use GetSqlValue and GetValue.
    // LargeUDT udt = (LargeUDT)reader.GetSqlValue(1);
    // LargeUDT udt = (LargeUDT)reader.GetValue(1);

    Console.WriteLine(
     "ID={0} LargeUDT={1}", id, udt);
  }
reader.close
}
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