Beginning Visual C++ 2005 (2006) [eng]-1

Updating Data Sources

this, viewID, &context);

pNewActiveView->OnInitialUpdate();

}

SetActiveView(pNewActiveView); // Activate the new view if(viewID==NEW_ORDER)

static_cast<CCustomerView*>(pNewActiveView)->SetNewOrderID();

pOldActiveView->SetDlgCtrlID(m_CurrentViewID); // Set the old view ID pNewActiveView->SetDlgCtrlID(AFX_IDW_PANE_FIRST);

}

All you do is check the viewID value. If it is NEW_ORDER you call the SetNewOrderID() member of the new view object. Because pNewActiveView is of type CView, you must cast it to the actual view type to call the member function.

Storing the Order Data

You don’t want to create a new entry in the Orders table until you have the first Product Details record for the order, so you need a way to pass the data accumulated in the CCustomerView object to the CProductView object. A simple way to do this is to define a new class to represent an order. It just needs to have a data member for each data value that you want to stash away. Except for the shipped date field that doesn’t sensibly have a value in a new order, the data members are the same as the data members corresponding to the fields in the COrderSet class. Create a new header file, Order.h, in the project, and add the following code to it:

// Stores the data for a new order #pragma once

class COrder

{

public:

//Data members same as fields in COrderSet long m_OrderID;

CString m_CustomerID; long m_EmployeeID; CTime m_OrderDate; CTime m_RequiredDate; long m_ShipVia; double m_Freight; CString m_ShipName; CString m_ShipAddress; CString m_ShipCity; CString m_ShipRegion;

CString m_ShipPostalCode; CString m_ShipCountry;

//Default constructor

COrder():

1019

Chapter 20

{

m_OrderDate = m_RequiredDate = CTime(Now); // Set time as today

}

};

In general it is not good practice to make all the data members of a class public like this, but because the recordset classes generated by the Class wizard all have public members, there is little to be gained by making them private in our class here.

If you add a data member, m_Order, of type COrder, to the Document Class, you will be able to use this to pass the order data to the CProductView object. All you have to do is get the CCustomerView object to load up the data members when the Select Products button is pressed, ready to be picked up by the CProductView object. You can implement the button handler in CCustomerView like this:

void CCustomerView::OnSelectproducts()

{

// Get a pointer to the document

CDBSimpleUpdateDoc* pDoc = static_cast<CDBSimpleUpdateDoc*>(GetDocument());

//Set up order field values from CCustomerSet object pDoc->m_Order.m_CustomerID = m_pSet->m_CustomerID; pDoc->m_Order.m_ShipAddress = m_pSet->m_Address; pDoc-> m_Order.m_ShipCity = m_pSet->m_City;

pDoc-> m_Order.m_ShipCountry = m_pSet->m_Country; pDoc-> m_Order.m_ShipName = m_pSet->m_CompanyName; pDoc-> m_Order.m_ShipPostalCode = m_pSet->m_PostalCode; pDoc-> m_Order.m_ShipRegion = m_pSet->m_Region;

//Set up order field values from CCustomerView dialog input

static_cast<CMainFrame*>(GetParentFrame())->SelectView(SELECT_PRODUCT);

}

This is straightforward stuff. You are just copying values from the recordset and record view objects to the Order object that is a member of the document object.

Setting Dates

There is a small problem with the date picker controls on the CCustomerView dialog: The variables corresponding to these, m_OrderDate and m_RequiredDate, are not initialized at the moment, so the controls do not display sensible values to start with. You want then to display the current date at the outset,

1020

Updating Data Sources

so you should add some code to initialize them at the end of the OnInitialUpdate() member called when the view object is first created:

void CCustomerView::OnInitialUpdate()

{

BeginWaitCursor();

GetRecordset();

CRecordView::OnInitialUpdate(); if (m_pSet->IsOpen())

{

CString strTitle = m_pSet->m_pDatabase->GetDatabaseName(); CString strTable = m_pSet->GetTableName(); if(!strTable.IsEmpty())

strTitle += _T(“:”) + strTable; GetDocument()->SetTitle(strTitle);

}

EndWaitCursor();

// Initialize time values SYSTEMTIME Now;

}

Here you set both CTime variables to the current time, just as you did in the constructor for the COrder class.

Now the CCustomerView object is in good shape. It displays the right date and it squirrels away all the value for the fields in a row in the Orders table, so you are ready to tackle the production selection process.

Selecting Products for an Order

When the view for selecting a product is displayed, you want to have the variables for the controls that display the order ID and the customer name already set up with appropriate values. You will get these values from the Order member of the document object. You can add a function to the CProductView class to do this. You can call it InitializeView() and the return type is void. You can call the function from the SelectView() member of the CMainFrame object for the application. That way you ensure that the controls are always initialized before the dialog box is displayed.

Before you implement InitializeView(), consider something else. The new Orders table record is added only when the Select Product button is clicked to add a product to the order for the first time. Subsequent button clicks should just add another product to the order, so you will need a way to determine whether the Orders table has been appended to or not when the button is clicked. You can do this by adding a variable, m_OrderAdded, of type bool to CProductView that is false to start with and set to true by the Select Product button handler. So add this variable to the class. You can initialize it in the InitializeView() member that you can implement as follows:

void CProductView::InitializeView()

{

1021

Chapter 20

// Get a pointer to the document

CDBSimpleUpdateDoc* pDoc = static_cast<CDBSimpleUpdateDoc*>(GetDocument());

m_OrderID = pDoc->m_Order.m_OrderID; m_CustomerName = pDoc->m_Order.m_ShipName;

}

This initializes the view class members for the order ID and customer name controls by copying values from the appropriate member of the Order member of the document. This function is also an opportunity to ensure that the controls for order quantity and discount start with suitable initial values. The order quantity for any product has to be at least 1, and the discount is 0 by default. Calling the inherited UpdateData() member with an argument value FALSE causes the data to be transferred from the class variables to the controls, as you saw previously. You will need to add an #include directive for DBSimpleUpdateDoc.h to the beginning of the source file to make the Document Class definition available.

To put this into operation, you just need to call InitializeView() whenever you switch to the product selection dialog box. The obvious place to do this is in the SelectView() member of the CMainFrame class:

//Get pointer to new view if it exists

//if it doesn’t the pointer will be null

CView* pNewActiveView = static_cast<CView*>(GetDlgItem(viewID));

//If this is first time around for the new view, the new view

//won’t exist, so we must create it

//The Order Details view is always created first so we don’t need

//to provide for creating that.

pNewActiveView = new CProductView; break;

default:

AfxMessageBox(_T(“Invalid View ID”)); return;

}

//Switching the views

//Obtain the current view context to apply to the new view

1022

Updating Data Sources

CCreateContext context;

context.m_pCurrentDoc = pOldActiveView->GetDocument(); pNewActiveView->Create(NULL, NULL, 0L, CFrameWnd::rectDefault,

this, viewID, &context);

pNewActiveView->OnInitialUpdate();

}

SetActiveView(pNewActiveView); // Activate the new view if(viewID==NEW_ORDER)

static_cast<CCustomerView*>(pNewActiveView)->SetNewOrderID(); else if(viewID == SELECT_PRODUCT)

static_cast<CProductView*>(pNewActiveView)->InitializeView();

pOldActiveView->SetDlgCtrlID(m_CurrentViewID); // Set the old view ID pNewActiveView->SetDlgCtrlID(AFX_IDW_PANE_FIRST);

}

When the viewID parameter has the value SELECT_PRODUCT, the CProductView class variables for the order ID and customer name controls will be initialized, as will the bool variable controlling the creation of a new record in the Orders table.

Adding a New Order

The final piece of the program that you have to put together is the code to add a new order. Adding an order is always done by the OnSelectproducts() member of CProductView. The effect of pressing the Select Products button depends on the value of the data member, m_OrderAdded. If it is false, the function should add a new record to the Orders table, as well as a new record to the Order Details table. If m_OrderAdded is true, only the Order Details table should have a new record added as this is another product for the same order. All the values you need for the new Orders record are stored in the m_Order member of the document. You just need to copy them to the members of the COrderSet object that is also a member of the document. The document object is in a strong position to deal with this, so add a member function, AddOrder() to CDBSimpleUpdateDoc with a bool return type, and implement it as:

m_OrderSet.m_CustomerID = m_Order.m_CustomerID; m_OrderSet.m_EmployeeID = m_Order.m_EmployeeID; m_OrderSet.m_Freight = m_Order.m_Freight;

1023

Chapter 20

m_OrderSet.m_OrderDate = m_Order.m_OrderDate; m_OrderSet.m_OrderID = m_Order.m_OrderID; m_OrderSet.m_RequiredDate = m_Order.m_RequiredDate; m_OrderSet.m_ShipAddress = m_Order.m_ShipAddress; m_OrderSet.m_ShipName = m_Order.m_ShipName; m_OrderSet.m_ShipPostalCode = m_Order.m_ShipPostalCode; m_OrderSet.m_ShipRegion = m_Order.m_ShipRegion; m_OrderSet.m_ShipVia = m_Order.m_ShipVia;

// No value for the Shipped Date field m_OrderSet.SetFieldNull(&m_OrderSet.m_ShippedDate);

}

else

AfxMessageBox(_T(“Cannot append to Orders table”));

}

You saw earlier in this chapter that the functions in a recordset object for adding and editing records can throw exceptions, so you put the code in a try block and catch any exceptions to avoid aborting the application if this happens.

After ensuring the COrderSet recordset is open, you check that the it allows records to be added by calling its CanAppend() member. Adding a new record involves three steps:

1.You first call the AddNew() member of the recordset. This starts the process and saves the current values of the data members in the recordset because you will be altering them and sets the values of the data members to null. This is nothing to do with null for pointers and it is not zero — null here implies no value has been set for a variable.

2.You set all the data members for the field values in the recordset to the values required in the record. This is quite straightforward. You just copy the values stored in the members of the m_Order object to the members of the recordset object. The m_ShippedDate member is null because you have not set a value for it here.

3.You call Update() to actually get the record written and this also restores the original values in the recordset object. It doesn’t apply here, but if you were displaying the recordset that you

were adding to, you would need to call the Requery() member of the recordset object to get the new record values displayed.

You can now put in the basic logic for the OnSelectproduct() handler for the CProductView class. You need to call UpdateData() for the view to get the data that was entered in the edit controls transferred to data members of the view object. Here’s the outline code for the handler function:

void CProductView::OnSelectproduct()

1024

// Get a pointer to the document

CDBSimpleUpdateDoc* pDoc = static_cast<CDBSimpleUpdateDoc*>(GetDocument());

if(m_OrderAdded)

// Code to add new Order Details record...

}

After calling the UpdateData() for the CProductView object, you get a pointer to the document object. You need this to call the AddOrder() member of the document that will do the work. Next you check the m_OrderAdded member. You only want to add a record to Orders when this is false. The AddOrder() member of the document object returns a bool value that is true if the order was added successfully, and false for any failure. You use this value to set the m_OrderAdded member of CProductView, and as an indicator for whether you can continue to add order details. You don’t need to display any message in the case of failure. The AddOrder() function has already done that.

The code to add a record to the Order Details table is also probably best handled by the document object, but the document class member function to do it needs access to four values from members of the CProductView and CProductSet classes — for the product ID, the order quantity, the unit price, and the applicable discount. The order ID is available in the document class from its m_Order member, so you don’t need to worry about that. You can add a function, AddOrderDetails(), to CDBSimpleUpdateDoc to add a record to the Order Details table. The return type should be void and the function has four parameters the ID of type long, price of type double, quantity of type int, and discount of type float.

You can implement the function as follows:

void CDBSimpleUpdateDoc::AddOrderDetails(long ID, double price, int quantity, float discount)

{

// Set Product Details recordset data member values m_DBSimpleUpdateSet.m_OrderID = m_Order.m_OrderID; m_DBSimpleUpdateSet.m_Quantity = quantity;

}

1025

Chapter 20

This sets up the values in the m_DBSimpleUpdateSet members and then updates the table in essentially the same way as for the Orders table. Again, you have to put the update code in a try block to catch any exceptions that might be thrown by AddNew() or Update().

You want to call this function every time the Select Product button handler in the CProductView class is called, so you can modify the handler to do this:

// Get a pointer to the document

CDBSimpleUpdateDoc* pDoc = static_cast<CDBSimpleUpdateDoc*>(GetDocument());

{

pDoc->AddOrderDetails(m_pSet->m_ProductID, m_pSet->m_UnitPrice,

}

}

You use the m_DBSimpleUpdateSet object to update the Order Details table. This was used by the original view in the application, and it is stored in the document object. You get the values for quantity and discount from the data members in the view object corresponding to the edit controls that provide for these values to be entered. The order ID value was set when the dialog was displayed so that it would be displayed for information only. The product ID and unit price values are retrieved from the CProductSet object associated with this view. After calling Update() to write the record, reset the values for quantity and discount back to their defaults.

After adding a number of other orders as you might deduce from the order ID, I added the order shown in Figure 20-19.

1026

Updating Data Sources

Figure 20-19

Then I clicked the Select Product button, and selected the product, the quantity, and discount shown in Figure 20-20.

Figure 20-20

1027

Chapter 20

Clicking the Select Product button adds that product to the order for the customer and then allows the selection of another product. Each click of the Select Product button adds a new record to the Order Details table for the current order ID. When the order is complete, just click the Done button to end the process.

After you add an order, you can verify that it was added correctly by moving to the last order in the order details browsing view as Figure 20-21 shows.

Figure 20-21

You may notice that the views don’t reset to the beginning of the recordset when you finish an order entry operation. Try the first exercise at the end of the chapter to fix this for the customer recordset. You should not find this too difficult.

Summar y

In this chapter you learned how elementary updating works using the ODBC support in MFC. The important points covered in this chapter include:

Updating is only possible if a recordset corresponds to a single table. Recordsets corresponding to table joins cannot be updated.

To start editing a record in a recordset you call the Edit() member of the recordset object.

To start adding a new record to a recordset, you call the AddNew() member of the recordset object.

1028