使用DAO访问数据库的例子(189KB).zip_dao

DaoLib 1.0 - A complete solution for real world database development. 1 - Requirements - Getting started 2 - Introduction 3 - Core components 4 - Intermediate abstractions 5 - User interface components 6 - Tutorial and code samples 7 - Deployment 8 - Feedback - Support 9 - Reference 1 - Requirements - Getting started Unzip the DaoLib file maintaining the directory structure (-d). This library requires Visual C++ 6.x installed on the development system. The evaluation version is fully functional, with a limit of 10 controls per dialog and an annoying reminder. 2 - Introduction The power of the DAO interface for dealing with databases is an undeniable fact. It provides a fast and reliable mechanism for data management of Access and other ISAM and ODBC databases. Though it was engineered targeting scripting languages such as Visual Basic and VBA, it provides a dual interface, which allows straightforward C and C++ handling of its methods and properties. The C/C++ developer has several options: a) Deal with COM interfaces such as DAODatabase, DAORecordset and the like using the OS built-in OLE support. This could be tedious and error prone, since the developer has to deal with reference counting, object releasing and other COM annoying aspects. b) Go up one level through a C++ proxy. Microsoft provides such a proxy-wrapper in its DAO library. This library is rowset-oriented and provides a valuable variable binding mechanism, but it is not the best solution for handling record-oriented applications. c) Use some framework which integrates the database specifics with a user interface management. MFC-DAO is an example of this approach. The problem here is that the integration is best suited for a Doc/View architecture, and it adds some complexity when dealing with dialog intensive applications. DaoLib was built with this three-level separation of concerns. It deals with all the COM burden, such as exception handling, reference counting and object lifespan. It provides a wrapper level you can access directly, and it integrates to MFC with little overhead. 3 - Core components The classes at this level are wrapped around DAO components. In addition, we provide a handful of helper classes such as Bstr, Variant and Currency, which encapsulate the BSTR, VARIANT and CURRENCY semantics, allowing a very robust parameter handling. ErrorInfo manages error handling, converting COM error objects into C++ exceptions. The instantiation of Dao objects was simplified through smart constructors, many of which take no arguments or a single string object. The enumerator semantics is replaced by a simpler indexing mechanism. The use of the 'property' Microsoft extension allows a 'VB-like' syntax in many cases: using Variant indexes, you can refer to a specific field as: FieldValue[0] or as: FieldValue["CustomerID"] In addition, the same property (if marked read/write) can be a left or right value. These are the core components and their mapping to DAO components: Field DAOField Recordset DAORecordset Database DAODatabase Workspace DAOWorkspace DBEngine DAODBEngine Parameter DAOParameter QueryDef DAOQueryDef TableDef DAOTableDef Index DAOIndex User DAOUser Group DAOGroup Relation DAORelation Connection DAOConnection Property DAOProperty These are the helper classes and their COM counterparts: Bstr BSTR Variant VARIANT Currency CURRENCY These have no counterparts: ErrorInfo Error handling through exception throwing. DaoBase Base class for every Dao component. It manages reference counting and object releasing. 4 - Intermediate abstractions In order to connect database objects with user interface elements such as controls, windows or dialogs, a couple of intermediate level abstract classes must be added to the hierarchy. These are DaoWindow and DaoControl. A windowing user interface element must inherit from DaoWindow and a control element from DaoControl to have complete control of its underlying database objects. They interact tightly with MFC transfer mechanisms. 5 - User interface components DaoLib comes with several user interface components, but its open architecture allows you to add your own custom components. The basic components are: Windowing components: DaoDialog DaoPropSheet DaoPropPage Control components: DaoEdit DaoCheck DaoRadio DaoGroup DaoCombo DaoListCtrl Complete components: ListDialog The windowing components are intended to be used as base classes of your dialog objects. You can create regular dialogs or property pages using the ClassWizard and then replace the base class in the declaration and add the constructor arguments. ClassWizard will still recognize your class and it even will use DaoDialog or DaoPropPage when adding base class references. The control classes can be used directly. Once again, you create control objects with ClassWizard and then replace their declaration (you can use the 'Replace' command if you have many controls). You can manage some attributes of the controls at declaration time, such as enabling or writing denial. DaoLib includes a powerful dialog-based component called ListDialog. It manages the display of Recordset objects through a list control, naming each header column upon the field's name and formatting the data according to each data type. In addition, it provides complete printing support for the list control's contents, sorting through column header clicking, keyboard support (Insert for adding records, Delete for deleting, Enter for viewing), and a mouse driven context menu with those same functions. 6 - Tutorial and code samples The use of the library does not require any special skill. If you use Visual C++ and feel comfortable with the ClassWizard, you can produce DaoLib code immediately. The steps to follow are: 1 - You can create a project without database support, or use an existing project. Add DaoLib.lib to the libraries in the project settings (Link page). Map the include path accordingly (C/C++ - Preprocessor). 2 - In your project's main file add a global DBEngine object: // The one and only CMyApp object CMyApp theApp; becomes: // The one and only CMyApp object DBEngine dbeng; CMyApp theApp; 3 - In the declaration of your App class, add the core #include and a Database object: #include "resource.h" // main symbols becomes: #include "resource.h" // main symbols #include "bordao.h" and: class CMyApp : public CWinApp { public: becomes: class CMyApp : public CWinApp { Database db; public: 4 - In InitInstance, add the Database initialization: CMainFrame* pFrame = new CMainFrame; m_pMainWnd = pFrame; becomes: try { db = "mydata.mdb"; //full path here, unless same Recordset::pdbase = &db; //directory as .EXE } catch(ErrorInfo& e) { e.Show(0); e.Destroy(); return FALSE; } CMainFrame* pFrame = new CMainFrame; m_pMainWnd = pFrame; 5 - Create the appropiate dialog resource. Assign each control an ID that resembles the name of the field with which it is associated. You can optionally add a Modify button (ID = 302). It must be the first in the control creation order. You may also add a Enter button (ID = 301). It must be non-visible, non-tabstop and marked as default button (unmark the OK button). 6 - Open the ClassWizard and create the CDialog as usual. For each control, assign a member variable (Category: Control) of the required type. If you want to use the macros provided with DaoLib (recommended), give each control the exact name of the corresponding field, prefixed with 'm_' (for a field named Custome