Hi Wacha,
On 7 March 2013 07:09, Wacha Gábor <[email protected]> wrote:
>
> I have a class for which I wrote the necessary type_conversion to load
> from and store to the database.
>
> My class has std::pair members, for which I use the following way to
> convert:
>
> static void from_base(values const & v, indicator & ind/* ind */,
> foo & bar {
> pair<char, unsigned int> temp;
>
> temp.first = v.get<int>("PAIR1");
> temp.second = v.get<int>("PAIR2");
> bar.setPair(temp);
> }
>
> And the to_base is similar:
>
> static void to_base(const foo & bar, values & v,
> indicator & ind) {
> v.set<int>("PAIR1", line.getPair().first);
> v.set<int>("PAIR2", line.getPair().second);
>
> }
>
> When I try to insert to the database, the first element of the pair is
> inserted, but the second element becomes zero.
> What happens?
I can't reproduce your problem in current Git master,
but perhaps I'm not testing exactly your case.
My version of test is attached in .cpp file or view gist of it here
https://gist.github.com/mloskot/5109226
If I misunderstood your case, can you post similar compilable sample with yours?
Also, please give exact version or SHA revision of SOCI you're using next time.
Little things, but usually shorten time-to-{test|answer} greatly.
> Actually when inserting happens, after each v.set(...)
> call the from_base is called.
Yes.
> I put the first element of the pair into the database, then from_base
> reads it back from values, and (because values does not yet contain the
> PAIR2 value) sets the second value to zero.
> Then with the call of v.set("PAIR2",...) it sets the value in the
> database to zero (or the default value).
>
> Should this happen? Is this a bug or it is mentioned somewhere in the
> documentation?
>
> Also, why should to_base call from_base after every call of values::set?
> It seems to be a great performance hit for me.
This is a good question and it caused confusions (see issues linked below) to
users as well as to other SOCI developers
Short answer is, this particular conversions occur is "by design".
Longer answer will follow as I'm going to explain it in the documentation
when I find some time.
Meanwhile, here is recent bug report related directly to this behaviour
and reported for broken stored procedures with IN/OUT parameters:
https://github.com/SOCI/soci/issues/81
where you will find some linked commits removing this "double conversion"
as optimisation. I fixed that problem restoring this "double conversion"
https://github.com/SOCI/soci/pull/88/
If you look at changes in files
src/core/type-conversion.h
src/core/use-type.cpp
you will see two longish comments that explain why we need to perform
convert_from_base() on data bound for use()
I hope this will clarify it better.
Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net
struct Paired
{
std::pair<int, int> p;
};
namespace soci
{
template<>
struct type_conversion<Paired>
{
typedef soci::values base_type;
static void from_base(values const &v, indicator /* ind */, Paired &pe)
{
std::pair<int, int> temp;
temp.first = v.get<int>("p1");
temp.second = v.get<int>("p2");
pe.p = temp;
}
static void to_base(Paired const &pe, values &v, indicator &ind)
{
v.set("p1", pe.p.first);
v.set("p2", pe.p.second);
ind = i_ok;
}
};
}
void test_pair()
{
try
{
session sql(backEnd, connectString);
try { sql << "drop table p "; } catch (...) {}
sql << "create table p (p1 integer, p2 integer)";
Paired p1;
p1.p = std::make_pair(1, 2);
sql << "insert into p (p1, p2) values (:p1, :p2)", use(p1);
p1.p = std::make_pair(3, 4);
sql << "insert into p (p1, p2) values (:p1, :p2)", use(p1);
Paired p2;
statement st = (sql.prepare << "select * from p", into(p2));
st.execute();
int count = 0;
while (st.fetch())
{
std::cout << p2.p.first << " - " << p2.p.second << std::endl;
}
}
catch (soci::soci_error const& e)
{
std::cout << e.what() << std::endl;
}
}------------------------------------------------------------------------------
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