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ADO Jumpstart (Con’t from page 6)

?.Number,.Description

EndWith

Next oError

Endif

On Error &cOldErr

If you are thinking, “Hey, maybe I should write a wrapper class

to better encapsulate and centralize code,” you’re on the right

track. The following code creates a custom class that can serve

as a starting point:

Local oRecordsetHandler

oRecordsetHandler = CreateObject("RecordsetHandler")

oRecordset.FieldS(”COmpaflyflame”).VaIUe

=

“Alfreds Futterkiste”

If loRecordsetHandler.Update(OReCOrdSet)

oRecordsetHandler.canCel(OReCOrdSet)

Endif

Define Class RecordsetHandler As Custom

Protected oRecordset

Protected ErrFlag

Procedure Update(oRecordset)

This.oRecordset = oRecordset

oRecordset.UpdateBatch

Return !This.ErrFlag

EndProc

Procedure Cancel(oRecordset)

This.oRecordset = oRecordset

oRecordset.Cancel

Return !ThIs.ErrFlag

EndProc

Procedure Error(nError, cMethod, nLine)

Local oError

For Each oError In;

This.oRecordset.ActlveConnectiOfl.ErrOrS

With oError

?.Number,.Description

End With

Next oError

Thls.ErrFlag = .T.

EndProc

EndDeflne

There’s a better way to determine whether an update proceeded

successfully. The preferred approach is to trap events that ADO

fires. Visual FoxPro by itself does not surface COM Events.

Fortunately, the new VFPCOM. DLL component provides this

capability to Visual FoxPro. The previous example can be

modified to show how using COM Events makes for more robust

code and class design.

Now we can improve the code of our example. Most of the time,

for efficiency, you will want to batch your updates that comprise

multiple records. Often, when you update multiple records,

transaction processing is required. In other words, either

updates to all records must succeed or none should occur. To

illustrate, let’s say you must apply a 10 percent price increase

to the products you sell. The prime requirement is that all

records in the Products table need modification. Without

transactional capabilities, the possibility exists that, for ex-

ample, after the first 10 records are updated, an error generated

April 2000

on the eleventh record prevents a complete update. Transaction

processing provides the ability to rollback changes.

The following example incorporates error trapping and the three

transaction methods of the Connection object:

Local Err,cOldErr

cOldErr = On(”error”)

On Error Err = .T.

oRecordset.Activeconnection.Begl nTra ns

Do While !oRecordset.Eof

If Err

Exit

Else

With oRecordset

.Fields(”unitprlce”).Value =;

.Fields(”unitprice”).Value * 1.1

.Movenext

EndWith

Endif

EndDo

oRecordSet.UpdateBatch

If Err

oRecordset.ActiveConnection.RollBackTrans

oRecordset.CancelBatch

Else

oRecordset.ActiveConnectlon.Com mitTrans

Endif

On Error &cOldErr

Additional operations you are likely to employ with recordsets

deal with adding new records and deleting existing records.

Both of these processes are very simple. The following code

adds a new record:

oRecordset.AddNew

As in Visual FoxPro, in ADO the new record becomes current.

Once the Add New method is invoked, the field can be populated

and, depending on the LockType, you then invoke either the

Update or UpdateBatch methods to modify the data source.

Deleting records is just as easy. The following code deletes the

current record:

oRecordset.Detete

Once again, after deleting the record, a call to Update or

UpdateBatch will update the data source.

(To be continued...]

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