Joost van der Sluis wrote:
If I could ask: where can I find a description of how TSQLQuery etc.
should be used for non-trivial applications? For example, if I want to
set up an explicit transaction, insert a few hundred rows of data, and
then make an explicit decision on whether I commit or rollback?
transaction.create
sqlquery.transaction := just created transaction.
sqlquery.sql := 'insert/update table ....'
for i := 0 to few hundred do
sqlquery.execsql
transaction.commit/rollback
I think I've got that. So TSQLQuery.ExecSql is good for statements that
don't return a result set- I don't have to go down to the connection
object to get this functionality.
I can see TSQLQuery.InsertSQL etc., but how should they be used? If I
want to force a lock on a table how should I do it?
In most cases you don't need them. The TSQLQuery is a TBufDataset. This
dataset fetches data from a source. (In DBExpress this source is a
dataprovider. In sqldb the source can be defined by a descendant, in
this case the TSQLQuery. But other sources are possible. It would also
be possible to create a descendant which uses a dataprovider-like
component)
The dataset is kept/cached in memory. The changes are kept in an
update-buffer.
When you call ApplyUpdates, all changes in the update-buffer are pushed
to the underlying dataset. (Again, this is handled in a descendant,
Delphi uses the dataprovider)
What TSqlQuery does when it has to push changes to the database-server,
is creating update/delete/insert sql-statements for each change. Well,
in fact it parses the provided SQL to see if it can create this
statements (using parameters) automatically.
So if I'm reading you correctly, ApplyUpdates in this case uses the .SQL
property with parameters...
There is a way however to provide these update/insert/delete statements
manually, that's where the .InsertSQL etc properties are for.
In fpc 2.4.2 and further the TBufDataset has one build-in mechanism of
data retrieval, which is streaming to a binary format. Or, when you add
the xmlstreaming unit, to the same xml format as TClientDataset uses.
..while this case uses .InsertSQL etc. What determines which case
applies- is it purely whether .InsertSQL etc. are defined?
Is there somewhere I can hook into the TSQLQuery to (a) see exactly what
query was passed to the server (b) collect any error text and (c) get
execution timing?
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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