DataCommand.DeriveSchema Method (String)
Derives the schema returned from a specified command. The schema indicates the layout of items and blocks in a data reader.
Namespace: Microsoft.VisualStudio.Data.Framework
Assembly: Microsoft.VisualStudio.Data.Framework (in Microsoft.VisualStudio.Data.Framework.dll)
Syntax
'Declaration
Public Function DeriveSchema ( _
command As String _
) As IVsDataReader
public IVsDataReader DeriveSchema(
string command
)
public:
virtual IVsDataReader^ DeriveSchema(
String^ command
) sealed
abstract DeriveSchema :
command:string -> IVsDataReader
override DeriveSchema :
command:string -> IVsDataReader
public final function DeriveSchema(
command : String
) : IVsDataReader
Parameters
command
Type: System.StringA command for which to derive the schema that is specific to a data source.
Return Value
Type: Microsoft.VisualStudio.Data.Services.SupportEntities.IVsDataReader
An IVsDataReader object. This object provides a forward-only, read-only data stream that describes the layout of items and blocks, that is, the schema, for the reader object returned upon executing the specified command.
Implements
IVsDataCommand.DeriveSchema(String)
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | The command parameter is nulla null reference (Nothing in Visual Basic). |
Remarks
The schema of the data reader returned by this method must follow a specific format. For each result that will be returned when you execute the command, there should be a result in the data reader. Each of these results should contain blocks that describe the items that will be returned when you execute the command. The description should contain the following items:
Name (String): the name of the item.
Ordinal (Int32): the position of the item.
UserDataType (String): the user data type of the item (for example, "myType").
NativeDataType (String): the native data type of the item (for example, "nvarchar").
ProviderDataType (Int32): the provider data type of the item (for example, System.Data.SqlDbType.NVarChar).
ProviderDbType (Int32): the generic ADO.NET data type of the item (for example, System.Data.DbType.StringFixedLength).
FrameworkDataType (Type): the .NET Framework data type of the item (for example, System.Int32).
Length (Int32): the maximum length of the item, if applicable.
Precision (Int32): the precision of the item, if applicable.
Scale (Int32): the scale of the item, if applicable.
Nullable (Boolean): the nullability of the item.
Those items that a provider does not support (for example, some forms of the data type) should be present but set to nulla null reference (Nothing in Visual Basic).
Note
Other exceptions that occur indicate that the schema derivation failed for a provider-specified reason.
.NET Framework Security
- Full trust for the immediate caller. This member cannot be used by partially trusted code. For more information, see Using Libraries from Partially Trusted Code.