Added the ViewReader

include/sqlgen/internal/from_str_vec.hpp

@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "../Result.hpp"
+#include "../parsing/ViewReader.hpp"
 
 namespace sqlgen::internal {
 
@@ -15,8 +16,12 @@ template <class T>
 Result<T> from_str_vec(
     const std::vector<std::optional<std::string>>& _str_vec) {
   T t;
-  const auto view = rfl::to_view(t);
-
+  auto view = rfl::to_view(t);
+  auto view_reader = parsing::ViewReader<remove_cvref_t<decltype(view)>>(&view);
+  const auto [err, num_fields_assigned] = view_reader.read(_str_vec);
+  if (err) {
+    return error(err->what());
+  }
   return t;
 }
 

include/sqlgen/parsing/ViewReader.hpp

@@ -0,0 +1,84 @@
+#ifndef SQLGEN_PARSING_VIEWREADER_HPP_
+#define SQLGEN_PARSING_VIEWREADER_HPP_
+
+#include <array>
+#include <optional>
+#include <rfl.hpp>
+#include <sstream>
+#include <string_view>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "../Result.hpp"
+#include "Parser.hpp"
+
+namespace sqlgen::parsing {
+
+template <class ViewType>
+class ViewReader {
+ private:
+  static constexpr size_t size_ = ViewType::size();
+
+ public:
+  ViewReader(ViewType* _view) : view_(_view) {}
+
+  ~ViewReader() = default;
+
+  std::pair<std::optional<Error>, size_t> read(
+      const std::vector<std::optional<std::string>>& _row) noexcept {
+    if (_row.size() != size_) {
+      std::stringstream stream;
+      stream << "Expected exactly " << std::to_string(size_)
+             << " fields, but got " << _row.size() << ".";
+      return std::make_pair(error(stream.str()), 0);
+    }
+    for (size_t i = 0; i < size_; ++i) {
+      const auto err = assign_to_field_i(
+          _row, i, &view_, std::make_integer_sequence<size_t, size_>());
+      if (err) {
+        return std::make_pair(err, i);
+      }
+    }
+    return std::make_pair(std::nullopt, size_);
+  }
+
+ private:
+  template <size_t i>
+  static void assign_if_field_is_field_i(
+      const std::vector<std::optional<std::string>>& _row, const size_t _i,
+      ViewType* _view, std::optional<Error>* _err) noexcept {
+    using FieldType = rfl::tuple_element_t<i, typename ViewType::Fields>;
+    using OriginalType = typename FieldType::Type;
+    using T =
+        std::remove_cvref_t<std::remove_pointer_t<typename FieldType::Type>>;
+    constexpr auto name = FieldType::name();
+    if (_i == i) {
+      auto res = Parser<T>::read(_row[i]);
+      if (!res) {
+        std::stringstream stream;
+        stream << "Failed to parse field '" << std::string(name)
+               << "': " << res.error().what();
+        *_err = Error(stream.str());
+        return;
+      }
+      rfl::get<i>(*_view) = std::move(*res);
+    }
+  }
+
+  template <size_t... is>
+  static std::optional<Error> assign_to_field_i(
+      const std::vector<std::optional<std::string>>& _row, const size_t _i,
+      ViewType* _view, std::integer_sequence<size_t, is...>) noexcept {
+    std::optional<Error> err;
+    (assign_if_field_is_field_i<is>(_row, _i, _view, &err), ...);
+    return err;
+  }
+
+ private:
+  ViewType* view_;
+};
+
+}  // namespace sqlgen::parsing
+
+#endif