Programming with ADO in Visual C ++ (below)

5. Record set traversal and update

According to the users table created by executing the SQL command just now, it contains four fields: ID, username, old, birthday
The following code enables you to open a record set, traverse all records, delete the first record, add three records, and move the cursor to the second record,
Change its age and save it to the database.
_ Variant_t vusername, vbirthday, vid, vold;
_ Recordsetptr m_precordset;
M_precordset.createinstance ("ADODB. recordset ");
M_precordset-> open ("select * from users ",
_ Variant_t (idispatch *) m_pconnection, true ),
Adopenstatic,
Adlockoptimistic,
Adcmdtext );
While (! M_precordset-> adoeof)
{
Vid = m_precordset-> getcollect (_ variant_t (long) 0); // obtain the value of the 1st column and count it from 0,
/// You can also directly give the column name, as shown in the following line
VUsername = m_pRecordset-> GetCollect ("username"); // obtain the value of the username field
VOld = m_pRecordset-> GetCollect ("old ");
VBirthday = m_pRecordset-> GetCollect ("birthday ");
/// Records in the OUTPUT window OUTPUT record set in DEBUG mode
If (vID. vt! = VT_NULL & vUsername. vt! = VT_NULL & vOld. vt! = VT_NULL & vBirthday. vt! = VT_NULL)
TRACE ("id: % d, name: % s, age: % d, birthday: % s/r/n ",
VID. lVal,
(LPCTSTR) (_ bstr_t) vUsername,
VOld. lVal,
(LPCTSTR) (_ bstr_t) vBirthday );
M_pRecordset-> MoveNext (); // move to the next record
}
M_pRecordset-> MoveFirst (); // move to the first record
M_pRecordset-> Delete (adAffectCurrent); // Delete the current record
/// Add three new records and assign values
For (int I = 0; I <3; I ++)
{
M_pRecordset-> AddNew (); // Add a new record
M_pRecordset-> PutCollect ("ID", _ variant_t (long) (I + 10 )));
M_pRecordset-> PutCollect ("username", _ variant_t ("Silverlight "));
M_pRecordset-> PutCollect ("old", _ variant_t (long) 71 ));
M_pRecordset-> PutCollect ("birthday", _ variant_t ("1930-3-15 "));
}
M_pRecordset-> Move (1, _ variant_t (long) adBookmarkFirst); // Move a record from the first record to the second record.
M_pRecordset-> PutCollect (_ variant_t ("old"), _ variant_t (long) 45); // modify the age
M_pRecordset-> Update (); // save it to the database.
Note: multiple queries can make the query process into a function executesql that allows m_precordset to obtain the query result of the connection pointer m_pconnection.
Void executesql (_ connectionptr m_pconnection, _ recordsetptr m_precordset, cstring strsql)
{
// Execute the SELECT statement
BSTR bstrsql = strsql. allocsysstring ();
Try
{
M_precordset-> open (bstrsql, (idispatch *) m_pconnection, adopendynamic, adlockoptimistic, ad1_text );
// Adopendynamic: Dynamic adlockoptimistic optimistic blocking method adshorttext: Text query statement
}
Catch (_ com_error error)
{
Cstring errormessage;
Errormessage. Format ("% s", (lptstr) error. Description ());
Afxmessagebox (errormessage );
}
}
// Error handling:
3127 -- the target table is not found.
3092 -- the target table already exists
For example:
Catch (const _ com_error E)
{
Afxmessagebox (E. Description ());
Long errorcode = E. wcode ();
If (3127 = errorcode) afxmessagebox ("the table does not exist ");
If (3092 = errorcode) afxmessagebox ("the table already exists ");
Return false;
}