DataCommand Class

Artikel
10/02/2013

Provides the ability to build and execute data commands of various types against data sources, and to retrieve read-only results or a command status code.

Inheritance Hierarchy

System.Object
Microsoft.VisualStudio.Data.DataCommand

Namespace: Microsoft.VisualStudio.Data
Assembly: Microsoft.VisualStudio.Data (in Microsoft.VisualStudio.Data.dll)

Syntax

'Declaration
<GuidAttribute("E19F79F4-3219-423d-97A4-5A2B8A8F45F3")> _
Public MustInherit Class DataCommand

[GuidAttribute("E19F79F4-3219-423d-97A4-5A2B8A8F45F3")]
public abstract class DataCommand

[GuidAttribute(L"E19F79F4-3219-423d-97A4-5A2B8A8F45F3")]
public ref class DataCommand abstract

[<AbstractClass>]
[<GuidAttribute("E19F79F4-3219-423d-97A4-5A2B8A8F45F3")>]
type DataCommand =  class end

public abstract class DataCommand

The DataCommand type exposes the following members.

Constructors

	Name	Description
	DataCommand	Class constructor. Instantiates a new instance of the DataCommand class.

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Methods

	Name	Description
	CreateParameter	Creates a parameter object that can be passed into the DeriveSchema, Execute or ExecuteWithoutResultsmethods on a DataCommandclass instance.
	DeriveParameters	Derives the parameters that can be specified for a given command.
	DeriveSchema	Derives the schema returned from a specified command, indicating the layout of items and blocks in a data reader.
	Equals	Determines whether the specified object is equal to the current object. (Inherited from Object.)
	Execute	Executes a specified command, optionally with parameters, and returns read-only results.
	ExecuteWithoutResults	Executes a command, optionally with parameters, but does not request results, instead returning an integer indicating the outcome of the call.
	Finalize	Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as the default hash function. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Prepare	Prepares the specified command on the data source to be executed; the command may then be executed multiple times, with varying parameters.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

DDEX Providers can execute various types of commands against the data source. This may include, but is not limited to, SQL statements, procedures, and function calls. They may also expose the ability to prepare and derive parameters and schemas for commands.

The DataCommand class introduces the concept of a command type. A command type indicates a programmatic interpretation of a given command string. For example, a command type "Text" might tell the DDEX provider that the command string is a SQL statement that should be executed directly. On the other hand, a "TabularFunction" command type might tell the DDEX provider that the command string is the name of a table-valued function that should be executed using the appropriate method.

Underlying technologies like ODBC, OLE DB, and ADO.NET attempt to enumerate a set of allowable command types, typically as plain text, in table form, or as stored procedures. The DataCommand class extends this concept by relaxing the requirement that such a command type originate in a fixed enumeration. This provides enormous flexibility by allowing DDEX providers to add custom command types, including descriptions of how and when the commands can be used.

Note

To provide command execution capability, but asynchronously, use the DataAsyncCommandclass, which has a set of methods equivalent to those on the DataCommand class, but which operate asynchronously.

Classes derived from the DataCommand class should implement those methods that are supported by their DDEX provider implementation. The base implementation of each method simply throws a NotSupportedException.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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