On Fri, 14 Nov 2014, silvioprog wrote:
On Fri, Nov 14, 2014 at 11:11 AM, Michael Van Canneyt <mich...@freepascal.org>
wrote:
[...]
By the very nature of the problem: GetLastAutoIncValue simply cannot be
implemented in general.
In firebird, postgres, these values are generated using a
generator/sequence.
You don't know the name of the generator, and even if you did, it is
impossible to retrieve the value
that was used to fill your particular record because the
sequence/generator may have been updated
several thousands of times by the time your second statement arrives.
The only way to do this correctly is using a RETURNING clause when doing
the insert.
Indded.
The idea is to add [pfRefresh] to providerflags. When doing an insert,
the fields with this flag will
be added to the RETURNING clause and used to update the buffer.
Fields of type ftautoInc can be added to this list (i.e. they
automatically
get pfRefresh in their providerflags)
This approach will work on all SQL databases that support RETURNING.
(That should include any SQL database available today)
Just a suggestion: it would be nice to implement it using interface or abstract
class (like ConnectionDef). So if
a database X does not provide the RETURNING support, a "mortal programmer"
could do that by himself on his own
project. =D
I was planning some fallback mechanism, yes.
And a "class function SupportReturningClause : Boolean" or something similar.
Or maybe
TDBCapability = (lastID,returningclause);
TDBCapabilities = set of TDBCapability;
and
Class function DatabaseCapabilities : TDBCapabilities;
I don't really like using interfaces when things can be done more simple.
Michael.
--
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