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Thank you very much, sir.
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I'm currently moving a project over to OLE DB and I've run into a bit of a dilema. I've gotten the basics of OLE down and how to use the accessor to insert into a table. Here's my problem, the table that I'm entering into will be very large once the program starts being used so using the accessor to insert will more than likely kill the computer. The question, is there any way to use the accessor to do the insert without populating it?
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I take it you're using Visual C++, and native OLE DB with ATL? I've inserted rows into large tables before without any problem. You're using a "real" database, right? (I don't consider Microsoft Access or FoxPro as a real database.) I'm confused by this statement:
errenden wrote:
The question, is there any way to use the accessor to do the insert without populating it?
What is it that you don't want to populate? Are you talking about the "generic" query that the accessor uses by default, where it selects every row in the table? And you're concerned about the program selecting every row first, and then adding your new row to the end?
-Thomas
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I'm using Oracle 9i on the backend so no worries there. But yes I'm concerned about the memory usage/performance with the accessor selecting every row just to do an insert. I've thought about just doing performing a specific SELECT statement to pull some set default row in the database but that solution seems clunky at best.
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Beautiful! I use Oracle also. (I also had better luck using Oracle's provider, instead of the Microsoft OLE DB for Oracle provider.)
I've actually used that method (pull a default row)- I take the default "take everything" accessor, and change it into a "get me the row with this primary key" parameterized query. If the accessor returns a row, I know that the data already existed in the table. If the rowset is empty, then I set the values up and update the row. Of course, you can handle this by checking out HRESULT and etc to determine if the row already exists...
You probably want to create a command object instead of a rowset object. That way you can do direct insert/update/deletes, as well as run stored procedures. In fact, you might want to turn your insert into a stored procedure! Either way, at the top of the accessor, add in all your member variables (TCHARs, DOUBLEs, etc) just as if you were dealing with a rowset accessor. In fact, you might already have this if you created a default rowset accessor! Then, define your parameter map...
BEGIN_PARAM_MAP(CNAMEOFACCESSORAccessor)<br />
COLUMN_ENTRY(1, mFIRSTFIELD)<br />
COLUMN_ENTRY(2, mSECONDFIELD)<br />
COLUMN_ENTRY(ETC...)<br />
END_PARAM_MAP()
Make sure you defined mFIRSTFIELD and mSECONDFIELD and etc first.
Now, change up the default "rowset" command that you were given.
DEFINE_COMMAND(CNAMEOFACCESSORAccessor, _T("INSERT INTO MYTABLE VALUES (?, ?)"))
Look down at the in the command class that ATL built for the OpenRowset method. Look for
return CCommand<CAccessor<CNAMEOFACCESSORAccessor>>::Open(mSession);
You've gotta change the CCommand::Open parameters. (Look it up in the MSDN, search for "CCommand::Open".) Leave the first parameter as m_session. You can set the second parameter, szCommand, to NULL because you're using the Accessor for the command. The third parameter would be for a property set, if you defined any. (If you're calling an insert, I'd think you would... I used stored procedures so I can't say for sure, but I think you'd need DBPROP_UPDATABILITY.) The fourth parameter's important, that's a pointer (pRowsAffected) to the number of rows that got DML performed. In your case, this should come back as 1 for a successful insert. (Negative 1 means no rows affected, as does a NULL pointer.)
Hope this helps; or at least gives you something to search the VC++ help files and the web for!
Oh- for the code where I queried first for the data, and if I got no rows back, then I'd insert the data- I sorta cheated. (laughs) I defined an LPCSTR inside of the CCommand called MyQuery. Then, in OpenRowSet, instead of the CCommand<CAccessor<blah blah>>::Open(mSession) I would do CCommand<CAccessor<blah blah>>::Open(mSession, MyQuery) instead.
In my main code, before I did a m_MyObject.Open(), I'd first do m_MyObject.MyQuery = "select these,columns from this.table where pk1=? and pk2=?". (You need ?'s for placeholders.) Then I'd assign values for my m_commandMyObject's parameters- the ones in the param list- like _tcscpy(m_commandMyObject.m_PK1,W2T(BstrVariable)). You've gotta do that for each parameter! Finally I'd do m_commandMyObject.Open(). This would load up my accessor's column map with the row matching pk1 and pk2, OR, it would have null rows. Once it was opened successfully, I'd check the rowset by doing: if (m_MyObject.MoveFirst()==S_OK) then (show an error because the row existed already) else (update rowset). And to update the rowset, all I had to do was set the column values of the accessor, and call m_MyObject.SetData.
This allowed me to work with just one row at a time; fetch the row from the database based on the order number; if the rowset comes back empty, then it's okay to insert the row!
One more thing- if you do decide to use stored procedures, you'll need to add extra lines to your param_map. BEFORE each COLUMN_ENTRY(...) line in the PARAM_MAP, you need to tell the provider which direction that parameter will go. Here's an example, first variable is sent up to Oracle, second variable comes back from Oracle:
BEGIN_PARAM_MAP(CMYTABLEAccessor)<br />
SET_PARAM_TYPE(DBPARAMIO_INPUT)<br />
COLUMN_ENTRY(1, mFIRSTFIELD_IN)<br />
SET PARAM_TYPE(DBPARAMIO_OUTPUT)<br />
COLUMN_ENTRY(2, mRESULTVAR_OUT)<br />
END_PARAM_MAP()
So I hope all that helps; if you search the Visual Studio help files (or even msdn.microsoft.com) for CCommand::Open , all of this should be more clear. But you're correct, you don't have to do anything with a rowset if you're just inserting data. And you might want to use stored procedures; that way, you let Oracle take care of wondering if a row already exists or not. If you can find it, look for the "Microsoft OLE DB 2.0 Programmer Reference and Data Access SDK" book- it's been out of print for a while, so it's hard to find. To paraphrase every ADO book, "OLE DB is the best for database access. Since it's so hard, we'll use ADO in this book." That killed off the OLE DB books pretty quickly! I found mine on eBay for cheap. The ISBN is 0-7356-0590-4, but the info in the book is still available on msdn.microsoft.com, in the VC++ 6.0 help files, and I just checked my .NET MSDN help files- it's in there, too.
Let me know how it goes! Also, just curious- why are you using OLE DB? It seems like the .NET stuff has become faster than OLE DB; I'm actually transitioning my OLE DB VC++ programming to the .NET Framework. (I'm working right now with C#.NET and ADO.NET, once I get a little better with it, I'll turn it into Managed C++ code.)
Wow, this is one long reply.
-Thomas
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I found some stuff yesterday on binding paramaters in OLE DB and started to tinker with it. Your reply helps parse out some of what I've read, especially with the pRowAffected variable (I had completely missed it the first time around). I'll check out that book later today and see about picking it up.
Maybe you could also answer this question since finding info good solid info on OLE DB seems to be very elusive. I've been doing select statements using the Create command and binding two parameters, which I added to accessor .h file. Now I've attempted to expand this out to do a insert which requires four parameters, I added the other two parameters to the accessor file and now the select won't work unless I include the other two parameters I just added in, which defeats the purpose of the select. Thanks for all the help so far, I appreciate it.
To answer your last question, the reason we haven't moved over to C# and the whole .NET framework is due to the fact that .NET may not run on all of the client machines (some being very old and some may be running unix) and the fact that some of the current code uses lisp and we don't have the time to make sure C#.NET will run with it. Fun stuff. Once again, thanks for the help.
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I'm doing some homework (well kind of homework, its not graded or handed in, but recommended that you do it) and I know how do all the basic stuff but I want to put it all in a transaction that can rollback if something goes wrong. I know some of the keywords BEGIN TRANSACTION, ROLLBACK, COMMIT but I just don't know how to form it etc. Any help would be appreciated.
Matt Newman
...armed with what? spitballs!? - Zell Miller
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Well, it depends on what you are doing. However the basics are the same regardless
BEGIN TRANSACTION
-- Do stuff
IF @SOME_SUCCESS_CONDITION
COMMIT TRANSACTION
ELSE
ROLLBACK TRANSACTION
Obviously you can check for failures at each point you do something with the database and rollback and exit there if it didn't work. The idea being that either everything works, or it appears that nothing ever happened.
Do you want to know more?
Not getting the response you want from a question asked in an online forum: How to Ask Questions the Smart Way!
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Ok, basically I'm just doing insert commands, do I have to check if the inserts succeeded or if it fails will it automatically go to ROLLBACK? I guess I'm just not sure how to get the success condition.
Matt Newman
...armed with what? spitballs!? - Zell Miller
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If it is a single command then you don't need to transact it. SQL Server will do that for you (hence Transacted-SQL).
If you have a stored procedure with more than one command then you can check each command has succeeded e.g.
UPDATE authors SET au_id = '172 32 1176'
WHERE au_id = "172-32-1176"
IF @@ERROR = 547
print "A check constraint violation occurred"
Remember that the @@ERROR is only for the last command, so if you want to check its value a number of times in order to, say, perform different actions depending on what the error is you need to store it in the following statement.
DECLARE @errorCode int
UPDATE authors SET au_id = '172 32 1176'
WHERE au_id = "172-32-1176"
SELECT @errorCode = @@ERROR
IF @errorCode = 0
COMMIT TRANSACTION
IF @errorCode = 547
ROLLBACK TRANSACTION
Does this help?
Do you want to know more?
Not getting the response you want from a question asked in an online forum: How to Ask Questions the Smart Way!
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Colin Angus Mackay wrote:
Does this help?
Yeah, i think so. Basically what I am working on now requires multiple inserts and if one fails the whole then they all have to fail.
Matt Newman
...armed with what? spitballs!? - Zell Miller
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Hi people.
I am using ADO 2.5 type library in C++BUilder 5, I have a memory leak, and need to find a solution.
Basically I open a connection in a thread, keep it open, and make regular queries to the connection to get data. After I am done with each record set, I close the record set. Even if I end the thread and restart another, memory is not freed and keeps climbing. I will include relevant code here:
I have confirmed that the queries are one of the sources of the leak, because if I increase the frequency of the queries, the memory leak accelerates accordingly.
CoInitialize(NULL);
cn = CoConnection::Create();
rs = CoRecordset::Create();
cm = CoCommand::Create();
AnsiString ConnString = TagService->GetSetupConnectString();
// setup connection parameters
cn->ConnectionString = WideString(ConnString.c_str()).Detach();
cn->CommandTimeout = 15;
cn->CursorLocation = Adodb_tlb::adUseClient;
// open connection
cn->Open(NULL,NULL,NULL,adConnectUnspecified);
while(....)
{
cn->Errors->Clear();
rs->Open(WideString(Query.c_str()).Detach(), (IDispatch*)cn, Adodb_tlb::adOpenStatic, Adodb_tlb::adLockOptimistic,0);
// do stuff with the data here.
dummy2Var = 0;
p1 = rs->Fields->get_Item(dummy2Var);
PrinterName = (AnsiString)p1->get_Value();
rs->Close();
Sleep(....);
}
cn->Close();
cn->Release();
CoUninitialize();
Any help would be very appreciated
Best wishes to all!
André
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MC++ 
Ok. You can re post it to MC++ Thread. Sometime it may help you out eventhough it is Ado.net discussion.
Sreejith Nair
[ My Articles ]
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How can I Run SQL Server Agent from VB.NET and get execution status (i.e., Success or Failure). Using VB 6.0 I was able to Declare the connection WithEvents and then use the _ExecuteComplete event of the connection to determine when and how the SQL Server Agent completed the job. The same method doesn't seem to work with VB.NET.
Any help would be appreciated.
Thanks,
Emilio Crespo
ecrespo@pollotropical.com
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I'll try to explain this.
I have a Windows form with a datagrid.
The datagrid binding has been set as MyDataGrid.SetDataBinding(MyDataView, "")
The dataview has also a RowFilter to show only some records.
Now, the problem is that I need to do some calculations whenever something is changed in that table.
For that I use the RowChanged and RowDeleted events.
Now, I have no problems with rows deleted, or rows that are modified, but I do with rows added.
When I add a new row, the RowChanged event does fire, and checking the row property of the event argument I can verify all the data in that row is correct.
However, a that point, all the dataset methods don't seem to "see" that row.
Very strange because the row is being showed on the datagrid.
More strange, if I make any other change, the row becomes "available".
It was driving me crazy because a Select method executed on the datatable would not return the newly added row, but it would if other change was made subsequently.
Just to be sure, in the RowChangedEvent I saved the dataset at that stage using the WriteXml method, then I looked at it and it did not include the new row.
But if I check the count property of the datatable, it has increased by one.
so  it seems that by the time the RowChangedEvent is fired, the row is not available to the dataset methods even though the row IS available to the dataview 
to make things even weirder. I have some code that checks for data integrity in the RowChanged event, if the data is wrong is display a message box and then calls the RejectChanges() method of the row.
That in turn triggers the event again and it exits the procedure because the row is null.
Now if that happens (meaning, if I enter wrong data to trigger the rollback) all subsequent insertions work fine.
even weirder, if I exclude the event handler before calling RejectChanges() (so the RowChanged event won't be trigger by the rollback) the problem persists, meaning new rows are not "seen".
this does not make any sense to me, and only happens if I do my calculations from the RowChanged event. If I add a button and use the button's click event it's fine, so it looks that when the RowChanged event is fired, the new row is in a sort of intermediate state (not the added state but some unforseen state).
This looks like a bug, but I really have no clue what's going on.
I hope this is understandable, it's so weird that I can't make any sense of it.
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Hello All,
I'll start with professing my ignorance on this subject! I am calling a stored proc from a sql server 2000 db. The stored proc is as follows:
ALTER Procedure dbo.glpImportFromProcurement
@Account varchar(8000),
@Amount varchar(8000),
@JVType Char(3),
@SourceDocumentString varchar(80),
@SourceDocumentID Int,
@Vendor int
AS
/* Purpose: This imports all pre-encumberance, encumberance, expense, commitments to elite from procurement
Input: @Account - this is the account number(s) (comma seperated) that the transaction hits
@Amount - this is the amount(s) (comma seperated) that match the account number. The accounts must be in double quotes.
@JVType - "pre"(pre-encumberance), "enc"(encumberance), "exp"(expense) When an expense, it will also create the commitment
@SourceDocumentString - This is either the requisition#, PO#, or Invoice#. This is for display purposes for the client to link it to procurement manually
@SourceDocumentID - This is either the Requisition ID, PO ID, or Receipt ID. This is so we know where the transaction came from on a system level
@Vendor - This is the vendor ID for the transaction. We need this to finish the other side of the journal and for the commitment.
Output: Creates appropiate journal and if needed (expense items) a commitment
Return code
Zero = success
< Zero nothing to process
> Zero (failed) and raises
Last Modified:
*/
return 0
(This is just a shell proc that will be filled in later)
So..., when I execute this through my command object it seems to execute fine, but I never get the zero the proc is attempting to return, regardless of what execution method I try. Is there something I'm missing here? I had thought that it was necessary to declare one of the parameters as output in order to return a value.
Thanks,
Ryan
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Hello,
I have a question regarding stored procedure desing that provides the
optimal performance. Let's say we have a table Products that consists of
three columns: Name, Status, RegistrationTime. All columns are indexed and
users should be able to lookup data by any of the columns. We have two main
options to design stored procedures for data retrieval:
1. Design separate stored procedures for each search criteria:
LookupProductsByName, LookupProductsByStatus, LookupProductsByTime.
2. Write a generic stored procedure that will fit any search criteria:
CREATE PROCEDURE GetProducts (
@Name varchar(20),
@Status int = NULL,
@FromTime datetime = NULL,
@ToTime datetime = NULL)
AS BEGIN
SELECT
[Name],
[Status],
[RegistrationTime]
FROM [Products]
WHERE [Name]=CASE
WHEN @Name<>NULL THEN @Name
ELSE [Name]
END
AND [Status]=CASE
WHEN @Status<>NULL THEN @Status
ELSE [Status]
END
AND [RegistrationTime]>=CASE
WHEN @FromTimestamp<>NULL THEN @FromTimestamp
ELSE [RegistrationTime]
END
AND [RegistrationTime]<=CASE
WHEN @ToTimestamp<>NULL THEN @ToTimestamp
ELSE [RegistrationTime]
END
ORDER BY [RegistrationTime]
END;
The second option is very attractive, because it is obviously easier to
maintain such code. However, I am a little concerned about performance of
such stored procedure. It is not possible to foresee what index should be
used, index can only be selected each during procedure execution, because
search criteria can include either Name, Status or RegistrationTime. Will it
make this SP inefficient? Or perormance difference in such case is not big
(if any) and we should choose the second option because of its significant
code reduction?
Thanks in advance
Вагиф Абилов
MCP (Visual C++)
Oslo, Norway
Hex is for sissies. Real men use binary. And the most hardcore types use only zeros - uppercase zeros and lowercase zeros.
Tomasz Sowinski
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The 2nd option is not only less efficient than the first, it is less efficient than not using a stored procedure at all. It is also harder to maintain and optimize, because of the complexity.
In my experience, for user-searches, stored procedures are a poor fit. This is because user's demand compex, dynamic searches, and stored procedures are unable to efficiently handle that. In addition, such stored procedures become hellishly long and complex.
my blog
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But you wouldn't defent using SQL statements directly, would you? While I see your point regarding performance, I can't understand reasons for not using stored procedure, or at least user-defined functions. Yes, I agree, for Web searches it is hard to write tens of SPs just to cover all possible cases, but at least UDF makes it possible to pack the code inside the database and not expose SQL directly to clients.
BTW, thanks for the opinion regarding efficiency. Looks like too much of generalisation will harm performance.
Вагиф Абилов
MCP (Visual C++)
Oslo, Norway
Hex is for sissies. Real men use binary. And the most hardcore types use only zeros - uppercase zeros and lowercase zeros.
Tomasz Sowinski
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Well, since you asked...
I would (and do) use SQL statements directly, specially in a web-based applications. Stored procedures offer some benefits, but they also have some drawbacks, such as portability and maintainability. Personally, I almost never use them, but I accept that many people do.
The main benefit of stored procedures is one of security -- you can protect your database against adhoc user queries. In a web application, this benefit does not exist, because the user never has direct access anyway.
In other situations, there are alternatives such as writing a network service component (web service or .net remoting) as an intermediate layer. The business value of such a web service is far more than that of stored procedures.
my blog
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I see your point. Although in our team we try to avoid direct use of SQL. We have multiple tiers, and letting Web developers write SQL directly will make the system uncontrollable.
BTW, I just received a reference to this outstanding article: Dynamic Search Conditions in T-SQL[^]. Exactly on this subject.
Вагиф Абилов
MCP (Visual C++)
Oslo, Norway
Hex is for sissies. Real men use binary. And the most hardcore types use only zeros - uppercase zeros and lowercase zeros.
Tomasz Sowinski
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Steven Campbell wrote:
The main benefit of stored procedures is one of security -- you can protect your database against adhoc user queries. In a web application, this benefit does not exist, because the user never has direct access anyway.
It is always wise to reduce the attack surface of your application. Even if you think that someone cannot get that far in it is still wise to protect all layers as there will always be some bit of code that was writted by a recent graduate, or someone working late on a Friday night, that is not as well thought out that could let someone in.
Stored procedures also have the benefit of being precompiled, and therefor preoptimised. SQL Server 2000 has gone some way to optimising directly called SQL statements by caching the compiled versions so that if the query is run again it already has it in a compiled state and doesn't need to recompile it. But SPs will be precompiled always.
I would suggest the argument that direct SQL is better than Stored Procedures due to portability issues is a false one. Having worked on many database systems over the years I have found that even directly called SQL statements need to be changed when moving from one database system to another, so you are still not guaranteed portability calling SQL directly.
I would also suggest that the argument that directly called SQL statements are easier to maintain is incorrect. If you create stored procedures with a defined interface and the internal structure of the datamodel changes, all you need to do is change the Stored Procedure and everything that calls it will be no wiser to the changes further down. It has all the benefits of an extra layer of abstraction. Calling SQL directly on tables will mean that if the table changes then all the calls to it have to be updated and that can be a lot of work (especially if the database is used by many applications.)
Do you want to know more?
Not getting the response you want from a question asked in an online forum: How to Ask Questions the Smart Way!
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