[VC] accessing local database applications using ADO

1. initialize if (! AfxOleInit () {AfxMessageBox (_ T (COM library initialization failed !)); ReturnFALSE;} Initialization Method 2: CoInitialize () CoUninitialize () 2. Import msado15.dll (I put it in stdafx. h) # importmsado15.dllno _ namespacerename (EOF, ADOEOF), rename (BOF, ADOBOF) 3

1. initialize if (! AfxOleInit () {AfxMessageBox (_ T (COM library initialization failed !)); Return FALSE;} method 2 of initialization: CoInitialize () CoUninitialize () 2. Import msado15.dll (I put it in stdafx. h) # import msado15.dllno _ namespace rename (EOF, ADOEOF), rename (BOF, ADOBOF) 3

1. Initialization

If (! AfxOleInit () {AfxMessageBox (_ T ("COM library initialization failed! "); Return FALSE ;}

Method 2:

CoInitialize ()
CoUninitialize ()

2. Import msado15.dll (I put it under stdafx. h)

#import "msado15.dll"no_namespace rename("EOF","ADOEOF"),rename("BOF","ADOBOF")

3. Variable Declaration

_ ConnectionPtr m_pConnection; // _ RecordsetPtr m_pRecordset; CString m_strMdbName; // database name CString m_strMdbPath; // database path CString m_strSQL; // SQL statement CXmlDialog m_xmlDlg; // Save the record set when executing the select statement

4. Connect to the database

Void CMyAdoDlg: OnBnClickedLink () {// TODO: add the control notification handler code here if (m_strMdbName.IsEmpty () {AfxMessageBox (_ T ("Please select a database! "); Return;} // if (m_pConnection-> GetState () // error: if the object is not created, GetStateif (m_pConnection! = NULL) {if (m_pConnection-> GetState () AfxMessageBox (_ T ("the database is connected! "); ElseAfxMessageBox (_ T (" the data connection object has been created, but the database is not connected successfully! "); Return;} try {HRESULT hr; // hr = m_pConnection.CreateInstance (" ADODB. connection "); // okhr = m_pConnection.CreateInstance (_ uuidof (Connection); if (SUCCEEDED (hr) {CString strConnection = _ T (" Provider = 'Microsoft. jet. OLEDB.4.0 '; Data Source =' "); strConnection + = m_strMdbPath; strConnection + =" '"; _ bstr_t bstrConnection = (LPTSTR) (LPCTSTR) strConnection; m_pConnection-> ConnectionTimeout = 10; // set the connection time m_pConn Ection-> Open (bstrConnection, "", "", adModeUnknown); AfxMessageBox (_ T ("connection successful! ") ;}} Catch (_ com_error & e) {AfxMessageBox (e. Description ());}}

Note:
1. m_pConnection.CreateInstance (_ uuidof (Connection); Use the. Operator instead of->. Although m_pConnection is a pointer, CreateInstance is a function of the pointer rather than a function of the object to which the Pointer Points.
2. m_pConnection! = Null does not indicate that the database is connected.

5. Disconnect the database

Void CMyAdoDlg: OnBnClickedDisconnect () {// TODO: add the control notification handler code here if (m_pConnection = NULL) {AfxMessageBox (_ T ("no database object instance is created! "); Return;} else if (! M_pConnection-> GetState () {AfxMessageBox (_ T ("the database object instance has been created, but the database is not connected! "); Return;} try {m_pConnection-> Close ();/* m_pConnection-> Release (); */m_pConnection = NULL; // The above release is not called, because the overloaded operator = will call Release:/* template <> _ com_ptr_t & operator = (Interface * pInterface) throw () {if (m_pInterface! = PInterface) {Interface * pOldInterface = m_pInterface; m_pInterface = pInterface; _ AddRef (); if (pOldInterface! = NULL) {pOldInterface-> Release () ;}} return * this;} */AfxMessageBox (_ T ("database disconnected successfully! ");} Catch (_ com_error & e) {AfxMessageBox (e. Description ());}}

Note:
1,
/* M_pConnection-> Release ();*/
M_pConnection = NULL;
Let these two statements be called by colleagues. During debugging, there is always an interruption, because the = is reloaded, And the reloaded functions call Release ()

6. SQL statement execution

/* SQL: create table employee (name nvarchar (20), sex text (1), age int); drop table employee; insert into employee values ('xinlang ', 'male', 24); insert into employee values ('ximei', 'female ', 25); select * from employee; */void CMyAdoDlg: OnBnClickedExcute () {// TODO: add the control notification handler code UpdateData () here; if (m_strSQL.IsEmpty () {AfxMessageBox (_ T ("fill in the SQL statement! "); Return;} if (m_pConnection = NULL |! M_pConnection-> GetState () {AfxMessageBox (_ T ("connect to the database! "); Return;} if (m_pRecordset! = NULL) {if (m_pRecordset-> GetState () m_pRecordset-> Close ();/* m_pRecordset-> Release (); */m_pRecordset = NULL ;} try {HRESULT hr; hr = m_pRecordset.CreateInstance ("adodb. recordset "); if (reverse (hr) {m_pRecordset-> Open (_ bstr_t (m_strSQL), _ variant_t (IDispatch *) m_pConnection), adOpenDynamic, adLockOptimistic, adw.text ); // If an SQL statement executes insert into, delete, and other operations that do not return record sets, m_pRecordset is disabled after the open statement is executed. // then, m_pRecordset is used to execute the operation, The system will prompt "the operation is not allowed when the object is closed !", If m_pRecordset executes select, // after execution, m_pRecordset is not closed. Therefore, you can execute the save operation // m_strSQL.MakeUpper (); // if (-1! = M_strSQL.Find (_ T ("SELECT") if (m_pRecordset-> GetState () {_ variant_t vtSave; _ bstr_t bstr; CString strSaveFilePath = GetSavefilePath (); savefileHandle (strSaveFilePath); m_xmlDlg.SetXmlFilePath (strSaveFilePath); bstr = strSaveFilePath; vtSave. vt = VT_BSTR; vtSave. bstrVal = bstr. copy (); // void PutCollect (const _ variant_t & Index, const _ variant_t & pvar); // m_pRecordset-> PutCollect ("name", _ bstr_t ("bytes I "); // remarks: used to modify the information of the current record // m_pRecordset-> PutCollect (" sex ", _ bstr_t (" medium ")); /// m_pRecordset-> MoveLast (); // m_pRecordset-> PutCollect ("name", _ bstr_t ("nihao"); // remarks: used to modify the information of the current record. // m_pRecordset-> PutCollect ("age", _ bstr_t ("100"); // inline HRESULT _ Recordset :: save (const _ variant_t & Destination, enum PersistFormatEnum PersistFormat) m_pRecordset-> Save (vtSave, adPersistXML); // Save the obtained information to vtSaveint state = m_pReco Rdset-> GetState (); while (! M_pRecordset-> ADOEOF) {_ variant_t vr; // vr. vt = VT_LPSTR; // the error message returned when the value assignment fails. // _ variant_t GetCollect (const _ variant_t & Index); // vr = m_pRecordset-> GetCollect ("name "); // OK // vr = m_pRecordset-> GetCollect ("sex"); // okvr = m_pRecordset-> GetCollect ("age"); m_pRecordset-> MoveNext ();}} else {AfxMessageBox (_ T ("SQL Execution successful! ") ;}} Catch (_ com_error & e) {AfxMessageBox (e. Description ());}}

7. Process stored files (saved as XML)

// Obtain the path of the saved file CString CMyAdoDlg: GetSavefilePath () {CString strSaveFile; if (! M_strMdbPath.IsEmpty () {strSaveFile = m_strMdbPath; strSaveFile = strSaveFile. left (1 + strSaveFile. reverseFind ('\'); strSaveFile + = DEFAULT_SAVE_XML_NAME;} return strSaveFile;} // process saved files BOOL CMyAdoDlg: SavefileHandle (CString & strSaveFilePath) {if (PathFileExists (strSaveFilePath) {CString strNewFile = strSaveFilePath; strNewFile + = _ T (". bak "); if (PathFileExists (strNewFile) DeleteFile (strNewFile); CFile: Rename (strSaveFilePath, strNewFile);} return TRUE ;}

#define DEFAULT_MDB_NAME _T("shujuku.mdb")#define DEFAULT_SAVE_XML_NAME _T("SaveData.xml")