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title: "db_source | Microsoft Docs"
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---
# db_source
Creates a connection to a data source.  
  
## Syntax  
  
```  
  
      [ db_source(   
   db_source,   
   name,   
   hresult   
) ]  
```  
  
#### Parameters  
 *db_source*  
 The connection string used to connect to the data source. For the format of the connection string, see [Connection Strings and Data Links](https://msdn.microsoft.com/en-us/library/ms718376.aspx) in the Microsoft Data Access Components (MDAC) SDK.  
  
 *name* (optional)  
 When you use `db_source` on a class, *name* is an instance of a data source object that has the `db_source` attribute applied to it (see example 1). When you use `db_source` inline in a method implementation, *name* is a variable (local to the method) that can be used to access the data source (see example 2). You pass this *name* to the `source_name` parameter of **db_command** to associate the data source with a command.  
  
 `hresult` (optional)  
 Identifies the variable that will receive the `HRESULT` of this database command. If the variable does not exist, it will be automatically injected by the attribute.  
  
## Remarks  
 `db_source` creates a [CDataSource](../data/oledb/cdatasource-class.md) and a [CSession](../data/oledb/csession-class.md) object, which together represent a connection with an OLE DB consumer data source.  
  
 When you use `db_source` on a class, the `CSession` object becomes a member of the class.  
  
 When you use `db_source` in a method, the injected code will be executed within method scope, and the `CSession` object is created as a local variable.  
  
 `db_source` adds data source properties to a class or within a method. It is used in conjunction with **db_command** (which takes the `db_source` *name* parameter as its `source_name` parameter).  
  
 When the consumer attribute provider applies this attribute to a class, the compiler will rename the class to \_*YourClassName*Accessor, where *YourClassName* is the name you gave the class, and the compiler will also create a class called *YourClassName*, which derives from \_*YourClassName*Accessor.  In Class View, you will see both classes.  
  
 For an example of this attribute used in an application, see the samples [AtlAgent](http://msdn.microsoft.com/en-us/52bef5da-c1a0-4223-b4e6-9e464b6db409) and [MultiRead](http://msdn.microsoft.com/en-us/5a2a915a-77dc-492f-94b2-1b809995dd5e).  
  
## Example  
 This sample calls `db_source` on a class to create a connection to the data source `ds` using the Northwind database. `ds` is a handle for the data source, which can be used internally to the `CMyCommand` class.  
  
```  
// db_source_1.cpp  
// compile with: /LD  
#include <atlbase.h>  
#include <atlplus.h>  
#include <atldbcli.h>  
  
[  
  db_source(L"my_connection_string", name="ds"),  
  db_command(L"select * from Products")  
]  
class CMyCommand {};  
```  
  
## Requirements  
  
### Attribute Context  
  
|||  
|-|-|  
|**Applies to**|**class**, `struct`, member, method, local|  
|**Repeatable**|No|  
|**Required attributes**|None|  
|**Invalid attributes**|None|  
  
 For more information about the attribute contexts, see [Attribute Contexts](../windows/attribute-contexts.md).  
  
## See Also  
 [OLE DB Consumer Attributes](../windows/ole-db-consumer-attributes.md)