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SPT cursor fetching and progress displaying for SPT cursor downloading
Vlad Grynchyshyn, February 5, 2002
SQL Pass Through commands often can take a lot of time for running and returning the result set to the client. It is often usefult to show a progress bar in case of such lengthy process. Also, FetchAsNeeded option, available for views, could be very useful for SPT cursors as well. However, how we ca...
Summary
SQL Pass Through commands often can take a lot of time for running and returning the result set to the client. It is often usefult to show a progress bar in case of such lengthy process. Also, FetchAsNeeded option, available for views, could be very useful for SPT cursors as well. However, how we can open SPT cursor and set FetchAsNeeded option for it? Here is a sample code for opening the cursor in "FetchAsNeeded" mode, as well as a description of approach for organizing the progress bar for downloading large number of records. The samples are tested for SQL Server 7.0, though other servers probably could be used when their ODBC drivers support asynchronous downloading of records (Fetching). It is recommended to read the help file for CursorSetProp() and SQLSetProp() commands, as well as a description of option "FetchAsNeeded" and "FetchSize" for cursor. It is useful to know well about SQL Pass Through functions before reading this FAQ article. Special thanks to Fernando J S Alvares for a few ideas and forcing the investigate of this question.
Description
Below is a simple code that allows to open the SPT cursor in FetchAsNeeded mode with FetchSize = 300 records. You will require to change table name and specify correct database, user name and password on place of 'X'-es in the SQLStringConnect() function.
&& Connect to the server
nn = SQLStringConnect("Driver=SQL Server;Server=XXXXXX;Database=XXXXX;UID=XXXXX;"+;
 "PWD=XXXXXX;")

&& Change the FetchAsNeeded option default value
CursorSetProp("FetchAsNeeded",.T.,0)

&& Updated based on the thread FetchAsNeeded SPT blocking remote views? Thread #1145681 Message #1145743
CURSORSETPROP("AllowSimultaneousFetch",.T.,0) 
CursorSetProp("FetchSize",300,0)

&& FetchAsNeeded option requires asynchronous connection for SPT cursors
SQLSetProp(nn,"Asynchronous",.T.)


do while NOT USED("MyResult") && SQLEXEC() will return 0 till all records 
                              && fetched and returned to client. So, 
                              && when you want to fetch, just wait till alias created with
                              && first FetchSize number of records (300 in this sample)
=SQLExec(nn,"SELECT * FROM TEST","MyResult")
enddo

* return the default option value to .F.
CursorSetProp("FetchAsNeeded",.F.,0)
As you see, you can define default values for cursor properties for current application running. You can do this using "0" as a reference to cursor alais in CursorSetProp command. New cursors opened will automatically get these property values by default. So when we open a new SPT cursor, it is opened already with FetchAsNeeded option set to .T. and FetchSize property setting. So, now it is possible to display progress bar for SPT. To do this, just organize a loop that will download records. Repetitive calls to SQLEXEC() will allow to do this. For example, you can display the status in a wait window (add below code to previous example):
&& initial number of records equals to FetchSize
lnRecordsInterval = CursorGetProp("FetchSize","MyResult")
lnRecordsTotal = m.lnRecordsInterval
WAIT WINDOW "Records: " + str(m.lnRecordsTotal) NOWAIT NOCLEAR

&& loop till all records are downloaded
do while SQLExec(nn) = 0 && get next FetchSize records
	m.lnRecordsTotal = m.lnRecordsTotal + m.lnRecordsInterval
	WAIT WINDOW "Records: " + str(m.lnRecordsTotal) NOWAIT NOCLEAR
enddo

&& show exact final number of records
WAIT WINDOW "Records: " + str(reccount) + " (finished)" TIMEOUT 3
Fetching process could be calcelled by SQLCancel() function. In such case cursor will contain only records that were fetched at the moment SQLCancel() is called. This could be used sometimes to limit number of downloaded records at the client side when query returns too large record set. The loop like in this sample could be used also to organize progressive fetching for SPT cursors for any other purposes. A few warnings: 1. Do not use reccount() function over the cursor with FetchAsNeeded option set to .T. Call of the Recccount() function will force VFP to download (fetch) all records at once. So, it is not possible to get number of records currently fetched. Anyway, its strange, but VFPdisplays correctly number of records in the status bar, as well as "GO" function allows to set the record pointer outside of the eof() - records will be fetched till specified record number, that also could be used to fetch records using larger steps than defined by FetchSize property. Any function that move record pointer will also fetch records automatically. SCAN ALL is not an exception. To scan only records that are currently fetched, you will require to use GO TOP and SCAN NEXT XXX records. GO BOTTOM will also force downloading of all records. All this should be accounted in case of complex programs that do some processing of data. When cursor is used with FetchAsNeeded option set to .T., it is usual situation when some code force downloading of all records. 2. The connection handle will be busy till all records downloaded (SQLExec() retruns 1). This means that each SPT cursor that use "FetchAsNeeded" option for users should be based on the separate connection to the server. This also means that you cannot send any updates in SPT cursor by setting cursor properties "UpdatableFieldList", "UpdateNameList", "Tables", "SendUpdates" and "KeyFieldList", till all records are donwloaded and SQLEXEC() command returned 1. Well, if you use FetchAsNeeded option only to show a progrees of records downloading from server, it is ok to use a common connection. 3. Keep in mind that the default setting for FetchAsNeeded option should be set to .F. after opening of the SPT cursor. This is because your application probably have a lot of other SPT cursors or views, that you want to be not fetchable.
Vlad Grynchyshyn, Soft Serve
Vlad Grynchyshyn is senior developer and project manager at the Ukrainian company "Soft Serve Ltd.", that provides custom-developed software solutions in several areas with use of wide range of development tools and languages. Vlad works in the MS Solutions department of the company, and has experience working with many MS development tools, components, utilities and documentation. Most experience is related to Visual FoxPro, MS SQL Server, Visual Studio and Visual Basic. He is active member of Visual FoxPro and SQL Server community, author of several articles for Universal Thread WEB site and other VFP community forums. He was MS MVP 2001-2002. He has a MS MCP certificate in Visual FoxPro area.
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