IVsDataCommand.DeriveSchema Method (String, DataCommandType)

When implemented by a class, 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.Services.SupportEntities
Assembly:  Microsoft.VisualStudio.Data.Services (in Microsoft.VisualStudio.Data.Services.dll)

Syntax

'宣言
Function DeriveSchema ( _
    command As String, _
    commandType As DataCommandType _
) As IVsDataReader

IVsDataReader DeriveSchema(
    string command,
    DataCommandType commandType
)

IVsDataReader^ DeriveSchema(
    String^ command, 
    DataCommandType commandType
)

abstract DeriveSchema : 
        command:string * 
        commandType:DataCommandType -> IVsDataReader 

function DeriveSchema(
    command : String, 
    commandType : DataCommandType
) : IVsDataReader

Parameters

• command
  Type: System.String
  A command for which to derive the schema that is specific to a data source.

• commandType
  Type: Microsoft.VisualStudio.Data.Services.SupportEntities.DataCommandType
  A value from the DataCommandType enumeration representing the command type for the indicated command, specifying how to interpret the contents of the command parameter.

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.

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.DbType.StringFixedLength).

• FrameworkDataType (Type): the 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).

注意

Other exceptions that occur indicate that the parameter 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.

See Also

Reference

IVsDataCommand Interface

DeriveSchema Overload

Microsoft.VisualStudio.Data.Services.SupportEntities Namespace