---
title: "Implementing a Command Class for a Data Processing Extension | Microsoft Docs"
ms.date: 03/06/2017
ms.prod: reporting-services
ms.prod_service: "reporting-services-native"
ms.technology: extensions


ms.topic: reference
helpviewer_keywords: 
  - "data processing extensions [Reporting Services], commands"
  - "Command class"
  - "commands [Reporting Services]"
ms.assetid: 465ef8d1-c503-407c-8afd-58d620e344ee
author: maggiesMSFT
ms.author: maggies
---
# Implementing a Command Class for a Data Processing Extension
  The **Command** object formulates a request and passes it on to the data source. The command text can take many different syntactical forms, including text and XML. If results are returned, the **Command** object returns results as a **DataReader** object.  
  
 To create a **Command** class, implement <xref:Microsoft.ReportingServices.DataProcessing.IDbCommand>. Implement the <xref:Microsoft.ReportingServices.DataProcessing.IDbCommand.ExecuteReader%2A> method to return a result set as a **DataReader** object. The <xref:Microsoft.ReportingServices.DataProcessing.IDbCommand.ExecuteReader%2A> method of your **Command** class should include an implementation that takes a <xref:Microsoft.ReportingServices.DataProcessing.CommandBehavior> enumeration as an argument. If you deploy your data processing extension to Report Designer, provide an implementation that handles a <xref:Microsoft.ReportingServices.DataProcessing.CommandBehavior.SchemaOnly> case in the <xref:Microsoft.ReportingServices.DataProcessing.IDbCommand.ExecuteReader%2A> method. A schema-only implementation is used to supply Report Designer with a fields list. The **DataReader** object returned by the <xref:Microsoft.ReportingServices.DataProcessing.IDbCommand.ExecuteReader%2A> method needs to contain type and name information for the fields, or columns, in your result set.  
  
 Optionally, your **Command** class can implement <xref:Microsoft.ReportingServices.DataProcessing.IDbCommandAnalysis>. This interface enables an implementing class to analyze a query and return a list of parameters in the query. The functionality of the <xref:Microsoft.ReportingServices.DataProcessing.IDbCommandAnalysis> interface is only used in Report Designer. When you implement <xref:Microsoft.ReportingServices.DataProcessing.IDbCommandAnalysis>, you enable users of Report Designer to be prompted for parameters whenever a report is run in preview mode. In addition, you can view the parameters in the **Parameters** tab of the **Data Set** dialog.  
  
> [!NOTE]  
>  You should not implement <xref:Microsoft.ReportingServices.DataProcessing.IDbCommandAnalysis> if your custom data processing extension does not support parameters.  
  
 For a sample **Command** class implementation, see [SQL Server Reporting Services Product Samples](https://go.microsoft.com/fwlink/?LinkId=177889).  
  
## See Also  
 [Reporting Services Extensions](../../../reporting-services/extensions/reporting-services-extensions.md)   
 [Implementing a Data Processing Extension](../../../reporting-services/extensions/data-processing/implementing-a-data-processing-extension.md)   
 [Reporting Services Extension Library](../../../reporting-services/extensions/reporting-services-extension-library.md)