On 21 April 2013 10:38, Ricardo Muñoz <[email protected]> wrote:
> Hi, I've been trying to use boost::tuple with a boost::optional element and
> I get a bad::cast exception. Attached to this mail you can find the complete
> test case but here is small code snippet:
>
> That works:
> row_type get_last_row(soci::session& sql)
> {
> unsigned int id = 0;
> std::string str1;
> boost::optional<std::string> str2;
>
> sql << "SELECT id, str1, str2 from example ORDER BY id DESC LIMIT 1",
> soci::into(id), soci::into(str1), soci::into(str2);
This is simple conversion that is performed by SQLite 3 backend itself
which translates SQL type to C++ type as implemented in
sqlite3_standard_into_type_backend::post_fetch
> That does not:
> row_type get_last_row2(soci::session& sql)
> {
> row_type myrow;
>
> try
> {
> sql << "SELECT id, str1, str2 from example ORDER BY id DESC LIMIT 1",
> soci::into(myrow);
Shortly, this is known issue related to this report
https://github.com/SOCI/soci/issues/90
The row_type is mapped to dynamic-typed objects wrapped with type_holder
This is involves more complex conversion using the common layer
of type_conversion specialisations, and here is the problem.
If you look at type_conversion<unsigned int> in unsigned-types.h, you can see
a little hack for base_type being long long.
Now, at binding, statements creates type_holder<int> according to
bind_into<dt_integer> mapping in statement_impl - there is no
dt_unsigned_integer.
But, the conversion goes through type_holder<long long> which leads to
failure of dynamic_cast in type-holder.h:
type_holder<T>* p = dynamic_cast<type_holder<T> *>(this);
as this is type_holder<int> but T is long long, unrelated types.
Long story short, this is all related to lack of complete C++ integer
types support.
Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net
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