Record.hpp

// SPDX-License-Identifier: Apache-2.0
 
#pragma once
 
#include "../Utils.hpp"
#include "Field.hpp"
 
#include <reflection-cpp/reflection.hpp>
 
#include <concepts>
#include <limits>
 
/// @brief Represents a record type that can be used with the DataMapper.
///
/// The record type must be an aggregate type.
///
/// @see DataMapper, Field, BelongsTo, HasMany, HasManyThrough, HasOneThrough
/// @ingroup DataMapper
template <typename Record>
concept DataMapperRecord = std::is_aggregate_v<Record>;
 
namespace detail
{
 
template <std::size_t I, typename Record>
constexpr std::optional<size_t> FindPrimaryKeyIndex()
{
    static_assert(DataMapperRecord<Record>, "Record must satisfy DataMapperRecord");
    if constexpr (I < Reflection::CountMembers<Record>)
    {
        if constexpr (IsPrimaryKey<Reflection::MemberTypeOf<I, Record>>)
            return { I };
        else
            return FindPrimaryKeyIndex<I + 1, Record>();
    }
    return std::nullopt;
}
 
} // namespace detail
 
/// Declare RecordPrimaryKeyIndex<Record> to retrieve the primary key index of the given record.
template <typename Record>
constexpr size_t RecordPrimaryKeyIndex =
    detail::FindPrimaryKeyIndex<0, Record>().value_or((std::numeric_limits<size_t>::max)());
 
/// Retrieves a reference to the given record's primary key.
template <typename Record>
decltype(auto) RecordPrimaryKeyOf(Record&& record)
{
    // static_assert(DataMapperRecord<Record>, "Record must satisfy DataMapperRecord");
    // static_assert(RecordPrimaryKeyIndex<Record> != static_cast<size_t>(-1), "Record must have a primary key");
    return Reflection::GetMemberAt<RecordPrimaryKeyIndex<std::remove_cvref_t<Record>>>(std::forward<Record>(record));
}
 
namespace details
{
 
template <typename Record>
struct RecordPrimaryKeyTypeHelper
{
    using type = void;
};
 
template <typename Record>
    requires(RecordPrimaryKeyIndex<Record> < Reflection::CountMembers<Record>)
struct RecordPrimaryKeyTypeHelper<Record>
{
    using type = typename Reflection::MemberTypeOf<RecordPrimaryKeyIndex<Record>, Record>::ValueType;
};
 
} // namespace details
 
/// Reflects the primary key type of the given record.
template <typename Record>
using RecordPrimaryKeyType = typename details::RecordPrimaryKeyTypeHelper<Record>::type;
 
/// @brief Maps the fields of the given record to the target that supports the operator[].
template <typename Record, typename TargetMappable>
void MapFromRecordFields(Record&& record, TargetMappable& target)
{
    Reflection::EnumerateMembers(std::forward<Record>(record), [&]<std::size_t I>(auto const& field) {
        using MemberType = Reflection::MemberTypeOf<I, Record>;
        static_assert(IsField<MemberType>, "Record member must be a Field<> type");
        static_assert(std::is_assignable_v<decltype(target[I]), decltype(field.Value())>,
                      "Target must support operator[] with the field type");
        target[I] = field.Value();
    });
}