Custom Data Types

[MikeBakerCZ]

Hi,
can you please put some examples how to implement custom data types (like datetime, timestamp, array etc) ?

Thanks!

[tkozybski]

Hello.
I've been playing around with taopq and this works for me (for retrieving). Needs to specialize tao::pq::parameter_traits to make it work with exec parameters:

struct Employee {
    int Id;
    std::string Name;
    int Age;
    std::string Address;
    double Salary;

    Employee(int id, std::string name, int age, std::string address, double salary)
        : Id{ id }
        , Name{ std::move(name) }
        , Age{ age }
        , Address{ std::move(name) }
        , Salary{ salary }

    {
    }
};

namespace tao::pq {
template <>
struct result_traits<Employee> {
    [[nodiscard]] static Employee from(row value)
    {

        return {
            value.get<int>(0),
            value.get<std::string>(1),
            value.get<int>(2),
            value.get<std::string>(3),
            value.get<double>(4),
        };
    }

    static constexpr size_t size = 5;
};
}

This code works now

        auto res = conn->execute("SELECT * FROM COMPANY ORDER BY ID").vector<Employee>();
        for (auto const& entry : res) {
            std::cout
                << entry.Id
                << " : " << entry.Name
                << " : " << entry.Age
                << " : " << entry.Address
                << " : " << entry.Salary
                << '\n';
        }

[d-frey]

Sorry I haven't found the time for providing an answer to this question. In fact, I think I might need to think about a few things first, as the parameter traits are currently not convenient and safe enough, so I will think about some improvements before I can finally add an example and some documentation.

[omerbn]

Sorry I haven't found the time for providing an answer to this question. In fact, I think I might need to think about a few things first, as the parameter traits are currently not convenient and safe enough, so I will think about some improvements before I can finally add an example and some documentation.

Any news?

[d-frey]

Yes, I recently started to refactor some parameter-traits (now going for leaving a choice between text-based and binary-based parameter traits). It's not yet finished, but check out the example at

taopq/src/test/pq/traits.cpp

Lines 10 to 42 in e1e5cc0

	namespace example
	{
	class user
	{
	private:
	int a, b, c, d;
	public:
	explicit user( int i )
	: a( i ), b( i + 1 ), c( i + 2 ), d( i + 3 )
	{}
	[[nodiscard]] auto to_taopq_param() const noexcept
	{
	return std::tie( a, b, c, d );
	}
	};
	struct user2
	{
	int a, b, c, d;
	explicit user2( int i )
	: a( i ), b( i + 1 ), c( i + 2 ), d( i + 3 )
	{}
	};
	[[nodiscard]] auto to_taopq_param( const user2& v ) noexcept
	{
	return std::tie( v.a, v.b, v.c, v.d );
	}
	} // namespace example

user shows how to use a member method to allow a type to be used as a parameter for taopq, while user2 shows how to do so with an external function when you can't modify a type.

I still need to figure out a way how to select the traits in a better way as well as combine different traits properly. Also, I probably need to improve the result traits as well. Still a lot to do and not enough time. But maybe the current progress already helps?

[omerbn]

When we'll I be able to use this ? :)

[d-frey]

You can use it right now. I think to_taopq_param (member- or free-function) will be the "convenience customization point" for the future, only more sophisticated use cases will require actual specializations of the parameter traits class. There will be other improvements (hopefully, when I have more time), but I'll try not to break compatibility unnecessarily.