O/H Mike Kershaw έγραψε:
>
>
> Hi Mauro,
>
> Yes you can run nested transactions, it is possible under SQL Server, I
> should have asked actually which database you were using for the back end?
>
> You can also set save points and rollback points within your
> transactions so if part of it fails then you can roll back to different
> parts of the transaction depending on what you need.
>
> With the exception I believe your issue is arising because the for loop
> is within the BeginTrans call, a single rollback will always roll back
> entire transaction.
>
> "But, still a question: is really not possible to switch the behavior
> "exception => transaction closure" to the behavior "exception !=>
> transaction closure"?"
> Do you mean by this you only want the Transaction to roll back under
> certain exceptions? Sorry did quite get that bit.
>
> Mike.
mauro
as Mike pointed out, many things depend on the kind of database you use.
For example, if you want to be sure that your database supports transactions
at all then you have to code something like the following
uses ADODB ,OLEDB ;
if MyConnection.Connected then
try
FSupportsTransactions := MyConnection.Properties['Transaction
DDL'].Value > DBPROPVAL_TC_NONE;
except
FSupportsTransactions := False;
end;
ADO is a midware and Delphi's ADO component set is a wrapper around that
technology.
http://msdn.microsoft.com/en-us/library/ms675532(VS.85).aspx
ADO could be used to access anything that is accessible through an OLE DB
Provider,
that is a driver. That anything could be an SQL server database such as Oracle,
MS SQL
or Firebird or even an MS Access database, an MS Excel file, a text file and do
on.
So you have to query your driver, that Provider, for its capabilities.
As for nested transactions through ADO and Delphi's ADO components...
Avoid nested transactions if possible. ADO supports nested transactions but
I think, not sure though and please correct me here if I'm wrong, there is a
limit as to
how many nesting levels are acceptable. I think is 6 or something.
In any case (ADO or not), one should carefully configure transaction properties
and
that's especially true when it comes to nested transactions, in order to avoid
deadlocks.
Code taken from your message
MyAdoConnection.BeginTrans();
try
Insert in a MyTable1
for each row on a MyTable2
do Insert in a MyTable3 through
a) preparing MyADOQuery
b) executing MyADOQuery by
try
MyADOQuery.ExecSQL();
except // this is going to hide any failure
end;
MyAdoConnection.CommitTrans();
except
MyAdoConnection.RollbackTrans();
end;
The nested try..except is a bad practice
try
MyADOQuery.ExecSQL();
except // this is going to hide any failure
end;
Let any failure-exception to reach the outer except..end.
Otherwise your code will reach MyAdoConnection.CommitTrans()
even when the MyADOQuery.ExecSQL(); fails.
Theo
--
Regards
Theo
------------------------
Theo Bebekis
Thessaloniki, Greece
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