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Allow result_t to have a size() function if DbResult has a size() function.

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size() must be const, but can be arbitrary type.
size() may be wrong after first next has been called
This commit is contained in:
Aaron Bishop
2017-10-21 16:09:30 -04:00
parent f6cb213e55
commit fb84f9b4a9
3 changed files with 38 additions and 2 deletions
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32
include/sqlpp11/result.h
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@@ -38,6 +38,31 @@ namespace sqlpp
using type = std::input_iterator_tag;
};
namespace detail
{
template<class DbResult, class = void>
struct result_has_size : std::false_type {};
template<class DbResult>
struct result_has_size<DbResult, void_t<decltype(std::declval<DbResult>().size())>>
: std::true_type {};
template<class DbResult>
constexpr bool result_has_size_v = result_has_size<DbResult>::value;
template<class DbResult, class = void>
struct result_size_type { using type = void; };
template<class DbResult>
struct result_size_type<DbResult, void_t<decltype(std::declval<DbResult>().size())>>
{
using type = decltype(std::declval<DbResult>().size());
};
template<class DbResult>
using result_size_type_t = typename result_size_type<DbResult>::type;
}
template <typename DbResult, typename ResultRow>
class result_t
{
@@ -139,6 +164,13 @@ namespace sqlpp
{
_result.next(_result_row);
}
template<class Size = detail::result_size_type_t<DbResult>>
Size size() const
{
static_assert(detail::result_has_size_v<DbResult>, "Underlying connector does not support size()");
return _result.size();
}
};
} // namespace sqlpp