storage_t::transaction

bool transaction(std::function<bool()> f);

Begins transaction, executes lambda f passed as first argument and commits or rollbacks transaction depending on lambda return result.

Parameters

(1) f

Function to be executed within a transaction. Lambda expression or function pointer can be passed. Function passed must take zero arguments and must return bool value which indicates whether storage should COMMIT or ROLLBACK.

Return value

The result received from f. It is just passed outside if you need to know whether transaction committed. Just ignore it if you don't need it.

Example

auto storage = make_storage("db.sqlite",
                            make_table("users",
                                       make_column("id",
                                                   &User::id,
                                                   autoincrement(),
                                                   primary_key()),
                                       make_column("first_name",
                                                   &User::firstName),
                                       make_column("last_name",
                                                   &User::lastName),
                                       make_column("birth_date",
                                                   &User::birthDate),
                                       make_column("image_url",
                                                   &User::imageUrl),
                                       make_column("type_id",
                                                   &User::typeId)),
                            make_table("user_types",
                                       make_column("id",
                                                   &UserType::id,
                                                   autoincrement(),
                                                   primary_key()),
                                       make_column("name",
                                                   &UserType::name,
                                                   default_value("name_placeholder"))));

storage.sync_schema();

storage.transaction([&] () mutable {
    storage.remove_all<User>(where(lesser_than(&User::id, 100)));
    auto usersRemoved = storage.changes();
    cout << "usersRemoved = " << usersRemoved << endl;
    return true;
});

As you can see here we call [changes|storage_t::changes] member function to get removed rows amount. Without a transaction changed returns 0 (in case not-RAM storage).