Fetching Data

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After you open the data source, session, and rowset objects, you can fetch data. Depending on the type of accessor you are using, you might need to bind columns.

To fetch data

  1. Open the rowset using the appropriate Open command.

  2. If you are using CManualAccessor, bind the output columns if you have not already done so. To bind the columns, call GetColumnInfo, and then create an accessor with the bindings, as shown in the following example:

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    // From the DBViewer Sample CDBTreeView::OnQueryEdit
    // Get the column information
    ULONG ulColumns       = 0;
    DBCOLUMNINFO* pColumnInfo  = NULL;
    LPOLESTR pStrings      = NULL;
    if (rs.GetColumnInfo(&ulColumns, &pColumnInfo, &pStrings) != S_OK)
        ThrowMyOLEDBException(rs.m_pRowset, IID_IColumnsInfo);
    struct MYBIND* pBind = new MYBIND[ulColumns];
    rs.CreateAccessor(ulColumns, &pBind[0], sizeof(MYBIND)*ulColumns);
    for (ULONG l=0; l<ulColumns; l++)
    rs.AddBindEntry(l+1, DBTYPE_STR, sizeof(TCHAR)*40, &pBind[l].szValue, NULL, &pBind[l].dwStatus);
    rs.Bind();
  3. Write a while loop to retrieve the data. In the loop, call MoveNext to advance the cursor and test the return value against S_OK, as shown in the following example:

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    while (rs.MoveNext() == S_OK)
    {
        // Add code to fetch data here
        // If you are not using an auto accessor, call rs.GetData()
    }
  4. Within the while loop, you can fetch the data according to your accessor type.

    • If you use the CAccessor class, you should have a user record that contains data members. You can access your data using those data members, as shown in the following example:

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      while (rs.MoveNext() == S_OK)
      {
          // Use the data members directly. In this case, m_nFooID
          // is declared in a user record that derives from
          // CAccessor
          wsprintf_s("%d", rs.m_nFooID); 
      }
    • If you use the CDynamicAccessor or CDynamicParameterAccessor class, you can fetch data by using the accessing functions GetValue and GetColumn, as shown in the following example. If you want to determine the type of data you are using, use GetType.

      В CopyCode imageCopy Code
      while (rs.MoveNext() == S_OK)
      {
          // Use the dynamic accessor functions to retrieve your data.
      
          ULONG ulColumns = rs.GetColumnCount();
          for (ULONG i=0; i<ulColumns; i++)
          {
              rs.GetValue(i);
          }
      }
    • If you use CManualAccessor, you must specify your own data members, bind them yourself, and access them directly, as shown in the following example:

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      while (rs.MoveNext() == S_OK)
      {
          // Use the data members you specified in the calls to
          // AddBindEntry.
      
          wsprintf_s("%s", szFoo);
      }

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