Could you show a python example on how to make multiple entries either
being all inserted (each entry done by an insert statement) or none on any
error (e.g. ctrl-c)? I also want want to make sure no two python processes
simultaneously editing these entries.
I am not sure I fully understand how to implement this correctly.
On Thu, Jan 30, 2020 at 12:43 AM Keith Medcalf <kmedc...@dessus.com> wrote:
>
> On Wednesday, 29 January, 2020 22:45, Peng Yu <pengyu...@gmail.com> wrote:
>
> >In python sqlite3 program, if I call .execute() multiple times then
> >call .commit(). Does it ensure that all the sqlite3 commands specified
> >by execute()'s either all take effect or none effect?
>
> Mayhaps yes, mayhaps no. .commit() is merely syntactic sugar for
> .execute('COMMIT')
>
> Basically, the method does the following:
>
> if (sqlite3_get_autocommit(connection) == 0) {
> sqlite3_stmt* stmt = 0;
> sqlite3_prepare(connection, "COMMIT", -1, &stmt, NULL);
> if (stmt) {
> sqlite3_step(stmt);
> sqlite3_finalize(stmt);
> }
> }
>
> That is, if there is a transaction in progress on the connection, it does
> a commit. Mutatis mutandis for .rollback() doing a 'ROLLBACK' rather than
> commit.
>
> It makes sure that all changes made in the current transaction are
> committed to the database. If you are using "magical mode" then hopefully
> a transaction was started when you updated something however this is not
> guaranteed (such is the nature of magic). The "magical mode" of the
> sqlite3 wrapper decides when to BEGIN and COMMIT transactions on its own.
> Sometimes the magician is a little daffy though and gets it wrong so it may
> begin/commit/rollback whenever the magician feels like it, which may or may
> not be when you want.
>
> If you want to ensure that transactions BEGIN and COMMIT/ROLLBACK when
> *you* want them to then use explicit .execute('BEGIN') (or .execute('BEGIN
> IMMEDIATE') to start an immediate transaction) command to start a
> transaction on a connection opened with isolation_level=None. You can
> still use .commit() for .execute('COMMIT') and .rollback() for
> .execute('ROLLBAC') if you want. The connection has a property
> in_transaction that lets you test whether a transaction is in progress
> (True) or the database is in autocommit (False) mode.
>
> >In other words, if any error occurs while running the sqlite3 commands
> >specified in execute(), what happens?
>
> That depends on the nature of the error. If you put in a bad SQL
> statement (got a syntax error) then that statement did nothing. Otherwise
> it depends on the conflict resolution method in effect for the statement
> causing the error, which is usually ABORT (by default) and it just ABORTs
> the current statement.
>
> >Also, is .executemany() the same as calling .execute() many times?
>
> Yes. x.executemany(sql, stuff) is syntactic sugar for
>
> for e in stuff:
> x.execute(sql, e):
>
> --
> The fact that there's a Highway to Hell but only a Stairway to Heaven says
> a lot about anticipated traffic volume.
>
>
>
>
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>
--
Regards,
Peng
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