User Records
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The latest version of this topic can be found at User Records.
To use a static accessor (that is, an accessor derived from CAccessor), your consumer must have a user record. The user record is a C++ class that contains data elements to handle input or output. The ATL OLE DB Consumer Wizard generates a user record for your consumer. You can add methods to the user record for optional tasks like handling commands.
The following code shows a sample record that handles commands. In the user record, BEGIN_COLUMN_MAP represents a data rowset passed to the consumer from a provider. BEGIN_PARAM_MAP represents a set of command parameters. This example uses a CCommand class to handle the command parameters. The data members in the map entries represent offsets into one contiguous block of memory for each instance of the class. The COLUMN_ENTRY macros correspond to the PROVIDER_COLUMN_ENTRY macros on the provider side.
For more information about the COLUMN_MAP and PARAM_MAP macros, see Macros for OLE DB Consumer Templates.
class CArtists
{
public:
// Data Elements
CHAR m_szFirstName[20];
CHAR m_szLastName[30];
short m_nAge;
// Column binding map
BEGIN_COLUMN_MAP(CArtists)
COLUMN_ENTRY(1, m_szFirstName)
COLUMN_ENTRY(2, m_szLastName)
COLUMN_ENTRY(3, m_nAge)
END_COLUMN_MAP()
// Parameter binding map
BEGIN_PARAM_MAP(CArtists)
COLUMN_ENTRY(1, m_nAge)
END_PARAM_MAP()
};
Wizard-Generated User Records
If you use the ATL OLE DB Consumer Wizard to generate a consumer, you have the choice of using OLE DB Templates or OLE DB Attributes. The generated code is different in each case. For more information about this code, see Consumer Wizard-Generated Classes.
User Record Support for Multiple Accessors
For a detailed discussion of the scenarios in which you need to use multiple accessors, see Using Multiple Accessors on a Rowset.
The following example shows the user record modified to support multiple accessors on the rowset. Instead of BEGIN_COLUMN_MAP and END_COLUMN_MAP, it uses BEGIN_ACCESSOR_MAP and BEGIN_ACCESSOR for each accessor. The BEGIN_ACCESSOR macro specifies the accessor number (offset from zero) and whether the accessor is an autoaccessor. Autoaccessors call GetData to retrieve data automatically on a call to MoveNext. Nonautomatic accessors require you to explicitly retrieve the data. Use a nonautomatic accessor if you are binding to a large data field (like a bitmap image) that you might not want to retrieve for every record.
class CMultiArtists
{
public:
// Data Elements
CHAR m_szFirstName[20];
CHAR m_szLastName[30];
short m_nAge;
// Column binding map
BEGIN_ACCESSOR_MAP(CMultiArtists, 2)
BEGIN_ACCESSOR(0, true) // true specifies an auto accessor
COLUMN_ENTRY(1, m_szFirstName)
COLUMN_ENTRY(2, m_szLastName)
END_ACCESSOR()
BEGIN_ACCESSOR(1, false) // false specifies a manual accessor
COLUMN_ENTRY(3, m_nAge)
END_ACCESSOR()
END_ACCESSOR_MAP()
};