db_accessor

Article
01/03/2018

The latest version of this topic can be found at db_accessor.

Groups db_column attributes that participate in IAccessor-based binding.

Syntax

  
      [ db_accessor(   
   num,   
   auto   
) ]

Parameters

num
Specifies the accessor number (a zero-based integer index). You must specify accessor numbers in increasing order, using integers or defined values.

auto
A Boolean value that specifies whether the accessor is automatically retrieved (TRUE) or not retrieved (FALSE).

Remarks

db_accessor defines the underlying OLE DB accessor for subsequent db_column and db_param attributes within the same class or function. db_accessor is usable at member level and is used to group db_column attributes that participate in OLE DB IAccessor-based binding. It is used in conjunction with either the db_table or db_command attributes. Calling this attribute is similar to calling the BEGIN_ACCESSOR and END_ACCESSOR macros.

db_accessor generates a rowset and binds it to the corresponding accessor maps. If you do not call db_accessor, accessor 0 will automatically be generated, and all column bindings will be mapped to this accessor block.

db_accessor groups database column bindings into one or more accessors. For a discussion of the scenarios in which you need to use multiple accessors, see Using Multiple Accessors on a Rowset. Also see "User Record Support for Multiple Accessors" in User Records.

When the consumer attribute provider applies this attribute to a class, the compiler will rename the class to _YourClassNameAccessor, where YourClassName is the name you gave the class, and the compiler will also create a class called YourClassName, which derives from _YourClassNameAccessor. In Class View, you will see both classes.

Example

The following example uses db_accessor to group columns in the Orders table from the Northwind database into two accessors. Accessor 0 is an automatic accessor, and accessor 1 is not.

// cpp_attr_ref_db_accessor.cpp  
// compile with: /LD /link /OPT:NOREF  
#define _ATL_ATTRIBUTES  
#include <atlbase.h>  
#include <atldbcli.h>  
  
[ db_command(L"SELECT LastName, FirstName FROM Orders") ]  
class CEmployees {  
public:  
   [ db_accessor(0, TRUE) ];  
   [ db_column("1") ] LONG m_OrderID;  
   [ db_column("2") ] TCHAR m_CustomerID[6];  
   [ db_column("4") ] DBTIMESTAMP m_OrderDate;   
  
   [ db_accessor(1, FALSE) ];  
   [ db_column("8") ] CURRENCY m_Freight;  
};

Requirements

Attribute Context

Applies to	Attribute blocks
Repeatable	No
Required attributes	None
Invalid attributes	None

For more information about the attribute contexts, see Attribute Contexts.

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