Support for Composable Queries

[jadamwilson2]

I would like to conditionally compose queries based on optional parameters passed to a function. A simple example would be:

auto do_query(const std::optional<Date>& date, const std::optional<User>& user, const std::optional<size_t> hash) {
auto query = EmptyCondition{};
if (date) {
    query &= "date"_c == *date;
}
if (user) {
    query &= "user"_c == *user;
}
if (hash) {
    query &= "hash"_c == hash;
}

return session().and_then(
          sqlgen::read<std::vector<DataType>> |
          sqlgen::where(query).value();
}

Is something like this possible now? If not, is it possible to add?

[liuzicheng1987]

@jadamwilson2 , you can't quite do it like that. The problem is that the queries need to be checked at compile time and therefore they all have a different type.

Let me think about what an elegant solution for this problem might be.