重写动态访问器

当使用动态访问器如 CDynamicAccessor 时，命令 Open 方法将根据已打开的行集合的列信息自动为您创建访问器。 可以重写该动态访问器以精确控制列的绑定方式。

若要重写动态访问器，请将 false 作为最后一个参数传递到 CCommand::Open 方法。 这将防止 Open 自动创建访问器。 然后可以调用 GetColumnInfo，并为要绑定的每一列调用 AddBindEntry。 以下代码显示如何执行此操作：

USES_CONVERSION;
double   dblProductID;

CCommand<CDynamicAccessor> product;
// Open the table, passing false to prevent automatic binding 
product.Open(session, _T("Select * FROM Products"), NULL, NULL, DBGUID_DEFAULT, false);

ULONG         nColumns;
DBCOLUMNINFO*   pColumnInfo;
// Get the column information from the opened rowset.
product.GetColumnInfo(&nColumns, &pColumnInfo);

// Bind the product ID as a double.
pColumnInfo[0].wType          = DBTYPE_R8;
pColumnInfo[0].ulColumnSize = 8;
product.AddBindEntry(pColumnInfo[0]);

// Bind the product name as it is.
product.AddBindEntry(pColumnInfo[1]);

// Bind the reorder level as a string.
pColumnInfo[8].wType          = DBTYPE_STR;
pColumnInfo[8].ulColumnSize = 10;
product.AddBindEntry(pColumnInfo[8]);

// You have finished specifying the bindings. Go ahead and bind.
product.Bind();
// Free the memory for the column information that was retrieved in 
// previous call to GetColumnInfo.
CoTaskMemFree(pColumnInfo);

char*   pszProductName;
char*   pszReorderLevel;
bool   bRC;

// Loop through the records tracing out the information.
while (product.MoveNext() == S_OK)
{
   bRC = product.GetValue(1, &dblProductID);
   pszProductName   = (char*)product.GetValue(2);
   pszReorderLevel  = (char*)product.GetValue(9);

   ATLTRACE(_T("Override = %lf \"%s\" \"%s\"\n"), dblProductID,
      A2T(pszProductName), A2T(pszReorderLevel));
}

请参见

概念

使用访问器