I am sure that I'm overlooking some simple thing here.
With a FireDac connection, if I use a SQL query with a WHERE clause that, due to the content of the search parameter, would normally return an empty result set, the OPEN command returns an error instead "Cannot open / define command, which does not return result sets". Is this by design ? Every other Delphi DB connection tool I have used simply returns an empty result set with a record count of 0.
******************************* April 16
I believe Victoria is on the right track. I had never used Firedac before so assumed it was the behaviour as designed. However if I communicate with the same RDBMS using the MS SQL driver, I do not see this happen, so I suspect it is on the Datasnap end.
Related
If I have an ADO Connection with CursorLocationType.adUseClient and I use it to open a Recordset, then does setting the Recordset.CacheSize property have any effect?
From CacheSize Property
Use the CacheSize property to control how many records to retrieve at one time into local memory from the provider.
And from The Significance of Cursor Location:
In ADO, call for a client-side cursor by using the adUseClient CursorLocationEnum. With a non-keyset client-side cursor, the server sends the entire result set across the network to the client computer.
It seems to me that setting CacheSize will have no effect for a client-side cursor, because the records are already in local memory. But I can't find any official documentation that explicitly says this. I can only find blog posts like this one that says:
We will be using ClientSide cursors ... The CacheSize tells ADO to cache N number of rows on the cursor. Since we chose to have 10 records per page, I set the cache size to 10. ADO will grab the first 10 records, and cache those. It won't hit the database until you request any past the cached limit.
but this seems to contradict "the server sends the entire result set across the network to the client computer."
So what actually happens?
I'm updating an ancient codebase written in Delphi 7 using ODBC Express for database connectivity to Delphi Seattle 10 using FireDAC. Currently, ODBC Express OEDataset components are pointed at stored procs and defined with params at design-time, including an #Result param populated from the "Return" function of the Sybase SPs.
If I attempt a simple swap (with minimal adjustment) for FireDAC's TFDStoredProc component (defining params at design-time), I get an "invalid parameter type" error when I include the #Result parameter (DataType=ftInteger, ParamType=ptResult). Without the #Result parameter, the stored procedure executes fine, but then I can't access the "Return" value.
I've mucked about with ResourceOptions.UnifyParams, FetchItems.Items := [fiMeta], ExecFunc instead of ExecProc, leaving out the #Result param, etc etc.
I'm sure I'm missing something very obvious, but I've been banging my head on my desk for a day trying to figure this out. Does anybody have any advice?
As weird as it seems, the issue is simply that the ptResult parameter was added as the last parameter in the list (which is how it was done using ODBC Express). Moving the #Result param to the first position, and only the first position, fixes the issue. Now I'm going to have to scour the documentation to see where I missed that little tidbit...
I am trying to use Macros in FireDAC to Preprocess my SQL Queries. I have a TADQuery object on a Data Module with the SQL set to something like:
Select * from MyTable
join OtherTable on MyTable.Key = OtherTable.Key
&Where
Then in my code I do this:
WhereClause = 'stuff based on my form';
Query.MacroByName('Where').AsRaw := WhereClause;
Query.Open;
This has worked great for complicated queries because it lets me make sure my fields and join conditions are correct using the SQL Property editor.
My problem is when the SQL statements ends up invalid because of my where clause. Is there any way to see the SQL after pre-processing that is going to be executed? Right now I am catching the FireDac errors and showing the SQL that is on EADDBEngineException object. However that is still showing my original SQL with the macros. If I can't get to it after the error happens is there anyway to force the Macro replacement to take place so I can look at the SQL in the debugger to help me see what is wrong.
If it matters I am connecting to a MS Access database with the goal of moving to SQL Server in the near future.
Apart from using Text property, to monitor what SQL is actually going to the database engine, consider using the "FDMonitor" FireDAC utility. According to the DokWiki pages (below):
drop a TFDMoniRemoteClientLink component on your form,
Set its Tracing property to True,
Add the MonitorBy=Xxx connection definition parameter to your existing FDConnection component. You can do this in the IDE object inspector, by selecting your FDConnection component, expanding the Params property, and setting MonitorBy to mbRemote.
Note that the TFDMoniXxxxClientLink should come before TFDConnection in the data module or form creation order, so adjust this by right clicking on the form or data module, then Creation Order, and moving the TFDMoni.. component above the FDConnection.
Also, it's helpful in the options of the TFDMoniXxxxClientLink, to disable most of the events being recorded, otherwise all the data returned is also shown in the FireDAC monitor. Expand the EventKinds property, and turn all the event kinds off, except for perhaps ekConnConnect, ekConnPrepare, and ekCmdExecute.
Then open the FireDAC Monitor from the IDE, (Tools > FireDAC Monitor). Start your app only once the monitor is running. Double click on a trace event (in the Trace Output tab), and you will see the actual SQL sent to the database in the bottom pane.
It also seems likely that adding the EventType of ekConnPrepare as mentioned above, would show you when the query's Prepare is called, but I haven't played enough with it say for sure.
Please see the following pages on the DocWiki for more information:
Overview: FDMonitor
How to: Tracing and Monitoring (FireDAC)
Other FireDAC utilities: Utilities (FireDAC)
(Just to remove this question from list of unanswered questions)
From comments:
Well, I've roughly checked what's happening there and I'm still not
sure if calling Prepare (which is useless for you as I get) is the
minimal requirement to trigger that preprocessing. Though, the
preprocessed SQL, the one which is sent to the DBMS you can access
through the Text property (quite uncommon name for such property). – TLama Feb
21 '14 at 8:18
I have a very large block of SQL that I am trying to execute inside of Delphi, against a Microsoft SQL Database. I am getting this:
Multiple-step OLE DB operation generated errors.
Check each OLE DB status value, if available. No work was done.
The script has multiple sql IF statements followed by BEGIN and END blocks with invocations of stored procedures, declaration of variables, and EXEC inside that. Finally it returns some of the variable values by SELECT #Variable1 AsName1,#Variable2 AsName2....
The above multi-step error is coming in as an OLEException from ADO, not from the Delphi code, and happens after all the SQL exec-stored-procedure have occurred, and therefore I suspect it's firing this OLE exception when it reaches the final stage which SELECT #Variable1 AsName1,... to get back a few variable values for my program to see them.
I know about this retired/deprecated MS KB article, and this is unfortunately not my actual issue:
http://support.microsoft.com/kb/269495
In short that KB article says to fix a registry key and remove "Persist Security Info" from the connection string. That's not my problem. I'm asking this question because I found the answer already and I think that someone else who gets stuck here might not want to waste several hours finding potential issues when there are several that I have found after searching for solutions for several hours. Anyone who wants to add another answer with different options, is fine, and I'll select yours if it's reproducible, and if necessary I'll turn this one into a Community Wiki because there could be a dozen obscure causes for this "ADO recordset is in a bad mood and is unhappy with your T-SQL" exception.
I have found several potential causes that are listed in various sources of documentation. The original KB article in the question suggests removing the 'Persist Security Info' from my ADO connection string, however in a standalone test in an application with just a TADOConnection and a single TADOQuery, the presence or absence of Persist Security Info had no effect, nor did explicitly setting it True or False.
What DID fix it was removing this CursorType declaration:
CursorType=ctKeyset
What I have learned is that bidirectional ADO datasets are fine for SELECT * FROM TABLE in ADO but are not so fine for complex SQL scripts.
Potential source of this error is updating char field with large value.
Example: Form has edit box with max length property set to 20 characters and Oracle database table has field defined as char(10).
Updating with 10 characters (or less) will work fine while updating with more then 10 characters will cause 'Multiple step...' error on ADOQuerry.UpdateBatch().
You also have to know that CHAR will allways have 20 characters. Consider Trimming value in edit box. CHAR behaves different than VARCHAR2 type.
If you have a query with parameter ,check the number of parameters in the query is matched with script...!
I'm using Firebird 2.1, DBExpress Driver from DevArt and Delphi 2010. Some of my reports that used to work with Delphi 2006 stopped working and produced an error message indicating that "arithmetic exception, numeric overflow, or string truncation" had occurred. The error occurred at this point in my code:
cds.Data := dsProvider.Data;
I found the place in my SQL statement that caused the error:
iif(ytd.hPayType <> -1,t.sCode, 'NET') sPayType
T.sCode is a Varchar(10) field. My conclusion is that the query returns data to the dsProvider and that when the dsProvider.Data is passed to the cds.Data, the cds component sets the field width based on the first value it receives. I get the same error message if I change the "iif" to a CASE statement. I managed to work around the issue by doing this:
CAST(iif(ytd.hPayType <> -1,t.sCode, 'NET') AS varchar(10)) sPayType
Since this used to work in Delphi 2006 without the CAST, I assume that the new behavior is due to an update to the TClientDataset. It would be nice to have the old, more forgiving behavior. Is there a way to configure the ClientDataset to accept this without a complaint or do I need to just tell my users to CAST on string results based on iif and CASE statements?
I used to work a lot with firebird in my last job, this error happens when you already have a large (length) varchar field value stored in the db and you are trying to "get" the string in delphi, try updating the value in the db to a smaller (length) varchar. I'm not sure if will work for you but give it a try.
Well, with a little more experience, it looks like I am seeing this truncation error show up consistently with the Delphi 2010 version of ClientDatasets. If I find a resolution that does not involve having to use CAST in the query, I will post it here. But for now, I am going to close this posting.