VC Access database Technology (take Postgre as an example) __ database

  Source code: Refer to My resources "VC Access Postgre Database"   The most commonly used database access technology has the following several 1.      odbc--Open database interconnection ODBC provides a unified programming interface for the use of different relational databases. After you install a different database, you need to create an ODBC data source, 2.      dao--data Access object 3.      rdo--Remote Data Object 4.      OLE db--object connection with embedded database 5.      Ado--activex Data Objects   Here I explain the two methods I use: ODBC and ADO.   1.       odbc to create an ODBC data source in the installation database, use CDatabase and CRecordset two MFC classes to establish a connection to the database and access the database. 1.1              condition contains header file: #include <afxdb.h > Declaring member variables: CDatabase m_dbpostgre; 1.2              Connection Database         int nretval;        nretval = M_dbpostgre.openex (_t ("dsn=postgresql30w; Uid=postgre; Pwd=postgre "),                                                            cdatabase::openreadonly | Cdatabase::noodbcdialog);        if (nretval)        {               AfxMessageBox ("Connect database successful!") _t       } 1.3               Access Data        CRecordset recordset (&m_dbpostgre);        CString strSQL = _t ("SELECT * from Product");        recordset. Open (CRecordset::forwardOnly, strSQL, crecordset::readonly);          cdbvariant var;          WhilE (!recordset. IsEOF ())        {               Tag_productinfo Tagproductinfo;              //ID                recordset. GetFieldValue (_t ("ID"), Var);               Tagproductinfo.nproductid = var.m_ Ival;              //Name                recordset. GetFieldValue (_t ("Name"), tagproductinfo.strproductname);                 M_vecproductinfo.push_back (Tagproductinfo);                              recordset. MoveNext ();       }          recordset. Close ();   2.      ADO Technology ActiveX Data object. ADO based on OLE DB, the use of ADO technology to access the database, the actual call process is: ADO client through ADO access to OLE DB provided by the program, so that the access speed will be slower. If a relational database does not have an OLE DB provider, you can use ODBC's OLE DB provider to access ODBC and then use ODBC to access the ODBC-enabled database. 2.1              conditions l          header files and dynamic library loading #include <comdef.h> #include <atlbase.h> #pragma   warning ( disable:4146)   #import    "C:/Program files/common files/system/ado/msado15.dll"    named_ guids   rename ("EOF", "adoeof"),   rename ("BOF", "Adobof")   #pragma    warning ( default:4146)   using    namespace   ADODB; l         COM Component Loading        if (CoInitialize (NULL)!= 0)        {               AfxMessageBox ("Initialize COM library failed!") (_t);               return FALSE;       } l         Variable declaration         _connectionptr m_pconnection; 2.2              Connection Database         m_pconnection.createinstance (__uuidof (Connection));        m_pconnection->connectionstring = _t ("dsn=postgresql30w; Uid=postgre; Pwd=postgre ");        HRESULT hr = M_pconnection->open (_t (""), _t (""), _t (""), adconnectunspecified );        if (SUCCEEDED (HR))        {   & nbsp;          AfxMessageBox ("Connect database successful!");       } 2.3               Access database        _commandptr pcommand (Command);        _recordsetptr precordset (__uuidof (Recordset));        CString strSQL = _t ("SELECT * From/" pg_getproductinfo/"()");          try        {               pcommand->activeconnection=m_pconnection;               pcommand->commandtext=_bstr_t (strSQL);               Precordset=pcommand->execute ( Null,null,adcmdtext);       } &NBSP;&NBSP;&NBsp;    catch (_com_error & E)        {               AfxMessageBox (E.description ());               return;       }          _variant_t var;        int nrecordnum = Precordset->getrecordcount ();        while (!precordset->getadoeof ())        {               Tag_productinfo Tagproductinfo;                             //ID                var = precordset->getcollect (_t ("ID"));               tagproductinfo.nproductid= Var.intVal;              //Name                var = precordset->getcollect (_t ("Name"));               Tagproductinfo.strproductname = ( char*) _bstr_t (VAR);                 M_vecproductinfo.push_back (Tagproductinfo);                 Precordset->movenext ();       }          precordset->close ();        precordset.release ();   Summary:        now DAO and RDO these two technologies have been used very little, OLE DB and ADO are relatively new technologies, OLE DB is very powerful, But his support for automation is not very good. To better support Automation, Microsoft in OLE Based on DB, ADO has been developed to facilitate scripting languages such as VBScript, and languages such as vb,delphi to use ADO to Access databases easily.          The above two technologies are the same for different relational databases, with different data sources, names, passwords, and how SQL statements are invoked. For example: To invoke a stored procedure as an example SQLServer2000 invocation method is "{Call Sp_addmember ('%s ', '%s ',%d)}", if not with arguments, there is no parentheses, and if you have arguments, the string's arguments need to be marked with single quotes. The Postgre invocation method is "_t" ("Select/" pg_modifyoneproduct/"(%d, '%s ')", "/" is an escape character, because if the stored procedure name is prefixed with double quotes when the stored procedure is defined, at the time of the call, Be sure to add double quotes, which is what SQL should be. There is also a stored procedure that wants to return all the records in the table, then use the selece * from stored procedure name when invoking the stored procedure.   summed up so much, you are welcome to criticize correct.