Large UDTs

Artikkel
09/15/2021

User-defined types (UDTs) 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.

Note

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 CLR User-Defined Types.

Retrieving UDT Schemas Using GetSchema

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

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 and later
`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

SqlDataReader Considerations

The SqlDataReader has been extended beginning 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 ConnectionString.

The following methods of SqlDataReader will return a SqlBinary instead of a UDT when the Type System Version is set to SQL Server 2005:

The following methods will return an array of Byte[] instead of a UDT when the Type System Version is set to SQL Server 2005:

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

Specifying SqlParameters

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.

Retrieving Data Example

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
}

Using connection As New SqlConnection( _
    connectionString, commandString)
    connection.Open()
    Dim command As New SqlCommand(commandString, connection)
    Dim reader As SqlDataReader
    reader = command.ExecuteReader

    While reader.Read()
      ' Retrieve the value of the Primary Key column.
      Dim id As Int32 = reader.GetInt32(0)

      ' Retrieve the value of the UDT.
      Dim udt As LargeUDT = CType(reader(1), LargeUDT)

     ' You can also use GetSqlValue and GetValue.
     ' Dim udt As LargeUDT = CType(reader.GetSqlValue(1), LargeUDT)
     ' Dim udt As LargeUDT = CType(reader.GetValue(1), LargeUDT)

      ' Print values.
      Console.WriteLine("ID={0} LargeUDT={1}", id, udt)
    End While
    reader.Close()
End Using

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