BelongsTo.hpp

// SPDX-License-Identifier: Apache-2.0
 
#pragma once
 
#include "../DataBinder/Core.hpp"
#include "../DataBinder/SqlNullValue.hpp"
#include "../SqlStatement.hpp"
#include "../Utils.hpp"
#include "Error.hpp"
#include "Field.hpp"
 
#include <compare>
#include <optional>
#include <string_view>
#include <type_traits>
 
/// @brief Represents a one-to-one relationship.
///
/// The `TheReferencedField` parameter is the field in the other record that references the current record,
/// in the form of `&OtherRecord::Field`.
/// Other Field must be a primary key.
///
/// @tparam TheReferencedField The field in the other record that references the current record.
/// @tparam ColumnNameOverrideString If not an empty string, this value will be used as the column name in the database.
///
/// @ingroup DataMapper
///
/// @code
/// struct User {
///     Field<SqlGuid, PrimaryKey::AutoAssign> id;
///     Field<SqlAnsiString<30>> name;
/// };
/// struct Email {
///     Field<SqlGuid, PrimaryKey::AutoAssign> id;
///     Field<SqlAnsiString<40>> address;
///     BelongsTo<&User::id> user;
///     BelongsTo<&User::id, SqlRealName<"the_user_id">> user; // also possible to customize the column name
/// };
/// @endcode
template <auto TheReferencedField, auto ColumnNameOverrideString = std::nullopt>
class BelongsTo
{
    using SelfType = BelongsTo<TheReferencedField, ColumnNameOverrideString>;
 
  public:
    /// The field in the other record that references the current record.
    static constexpr auto ReferencedField = TheReferencedField;
 
    /// If not an empty string, this value will be used as the column name in the database.
    static constexpr std::string_view ColumnNameOverride = []() consteval {
        if constexpr (!std::same_as<decltype(ColumnNameOverrideString), std::nullopt_t>)
            return std::string_view { ColumnNameOverrideString };
        else
            return std::string_view {};
    }();
 
    /// Represents the record type of the other field.
    using ReferencedRecord = MemberClassType<decltype(TheReferencedField)>;
 
    static_assert(std::remove_cvref_t<decltype(std::declval<ReferencedRecord>().*ReferencedField)>::IsPrimaryKey,
                  "The referenced field must be a primary key.");
 
    /// Represents the column type of the foreign key, matching the primary key of the other record.
    using ValueType = typename std::remove_cvref_t<decltype(std::declval<ReferencedRecord>().*ReferencedField)>::ValueType;
 
    static constexpr auto IsOptional = true;
    static constexpr auto IsMandatory = !IsOptional;
    static constexpr auto IsPrimaryKey = false;
    static constexpr auto IsAutoIncrementPrimaryKey = false;
 
    template <typename... S>
        requires std::constructible_from<ValueType, S...>
    constexpr BelongsTo(S&&... value) noexcept:
        _referencedFieldValue(std::forward<S>(value)...)
    {
    }
 
    constexpr BelongsTo(ReferencedRecord const& other) noexcept:
        _referencedFieldValue { (other.*ReferencedField).Value() },
        _loaded { true },
        _record { std::make_unique<ReferencedRecord>(other) }
    {
    }
 
    constexpr BelongsTo(SelfType const& other) noexcept:
        _referencedFieldValue(other._referencedFieldValue),
        _loader(std::move(other._loader)),
        _loaded(other._loaded),
        _modified(other._modified),
        _record(other._record ? std::make_unique<ReferencedRecord>(*other._record) : nullptr)
    {
    }
 
    constexpr BelongsTo(SelfType&& other) noexcept:
        _referencedFieldValue(std::move(other._referencedFieldValue)),
        _loader(std::move(other._loader)),
        _loaded(other._loaded),
        _modified(other._modified),
        _record(std::move(other._record))
    {
        other._loaded = false;
    }
 
    BelongsTo& operator=(SqlNullType /*nullValue*/) noexcept
    {
        if (!_referencedFieldValue)
            return *this;
        _loaded = false;
        _record = std::nullopt;
        _referencedFieldValue = {};
        _modified = true;
        return *this;
    }
 
    BelongsTo& operator=(ReferencedRecord& other)
    {
        if (_referencedFieldValue == (other.*ReferencedField).Value())
            return *this;
        _loaded = true;
        _record = std::make_unique<ReferencedRecord>(other);
        _referencedFieldValue = (other.*ReferencedField).Value();
        _modified = true;
        return *this;
    }
 
    BelongsTo& operator=(SelfType const& other)
    {
        if (this == &other)
            return *this;
 
        _referencedFieldValue = other._referencedFieldValue;
        _loader = std::move(other._loader);
        _loaded = other._loaded;
        _modified = other._modified;
        _record = other._record ? std::make_unique<ReferencedRecord>(*other._record) : nullptr;
 
        return *this;
    }
 
    // clang-format off
 
    /// Marks the field as modified or unmodified.
    LIGHTWEIGHT_FORCE_INLINE constexpr void SetModified(bool value) noexcept { _modified = value; }
 
    /// Checks if the field is modified.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr bool IsModified() const noexcept { return _modified; }
 
    /// Retrieves the reference to the value of the field.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ValueType const& Value() const noexcept { return _referencedFieldValue; }
 
    /// Retrieves the mutable reference to the value of the field.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ValueType& MutableValue() noexcept { return _referencedFieldValue; }
 
    /// Retrieves a record from the relationship.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord& Record() { RequireLoaded(); return *_record; }
 
    /// Retrieves an immutable reference to the record from the relationship.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord const& Record() const { RequireLoaded(); return *_record; }
 
    /// Checks if the record is loaded into memory.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr bool IsLoaded() const noexcept { return _loaded; }
 
    /// Unloads the record from memory.
    LIGHTWEIGHT_FORCE_INLINE void Unload() noexcept { _record = nullptr; _loaded = false; }
 
    /// Retrieves the record from the relationship.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord& operator*() noexcept { RequireLoaded(); return *_record; }
 
    /// Retrieves the record from the relationship.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord const& operator*() const noexcept { RequireLoaded(); return *_record; }
 
    /// Retrieves the record from the relationship.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord* operator->() { RequireLoaded(); return _record.get(); }
 
    /// Retrieves the record from the relationship.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord const* operator->() const { RequireLoaded(); return _record.get(); }
 
    /// Checks if the field value is NULL.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr bool operator!() const noexcept { return !_referencedFieldValue; }
 
    /// Checks if the field value is not NULL.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr explicit operator bool() const noexcept { return static_cast<bool>(_referencedFieldValue); }
 
    // clang-format on
 
    /// Emplaces a record into the relationship. This will mark the relationship as loaded.
    [[nodiscard]] LIGHTWEIGHT_FORCE_INLINE constexpr ReferencedRecord& EmplaceRecord()
    {
        _loaded = true;
        _record = std::make_unique<ReferencedRecord>();
        return *_record;
    }
 
    LIGHTWEIGHT_FORCE_INLINE void BindOutputColumn(SQLSMALLINT outputIndex, SqlStatement& stmt)
    {
        stmt.BindOutputColumn(outputIndex, &_referencedFieldValue);
    }
 
    template <auto OtherReferencedField>
    std::weak_ordering operator<=>(BelongsTo<OtherReferencedField> const& other) const noexcept
    {
        return _referencedFieldValue <=> other.Value();
    }
 
    template <detail::FieldElementType T, PrimaryKey IsPrimaryKeyValue = PrimaryKey::No>
    std::weak_ordering operator<=>(Field<T, IsPrimaryKeyValue> const& other) const noexcept
    {
        return _referencedFieldValue <=> other.Value();
    }
 
    template <auto OtherReferencedField>
    bool operator==(BelongsTo<OtherReferencedField> const& other) const noexcept
    {
        return (_referencedFieldValue <=> other.Value()) == std::weak_ordering::equivalent;
    }
 
    template <auto OtherReferencedField>
    bool operator!=(BelongsTo<OtherReferencedField> const& other) const noexcept
    {
        return (_referencedFieldValue <=> other.Value()) != std::weak_ordering::equivalent;
    }
 
    template <detail::FieldElementType T, PrimaryKey IsPrimaryKeyValue = PrimaryKey::No>
    bool operator==(Field<T, IsPrimaryKeyValue> const& other) const noexcept
    {
        return (_referencedFieldValue <=> other.Value()) == std::weak_ordering::equivalent;
    }
 
    template <detail::FieldElementType T, PrimaryKey IsPrimaryKeyValue = PrimaryKey::No>
    bool operator!=(Field<T, IsPrimaryKeyValue> const& other) const noexcept
    {
        return (_referencedFieldValue <=> other.Value()) != std::weak_ordering::equivalent;
    }
 
    struct Loader
    {
        std::function<void()> loadReference {};
    };
 
    /// Used internally to configure on-demand loading of the record.
    void SetAutoLoader(Loader loader) noexcept
    {
        _loader = std::move(loader);
    }
 
  private:
    void RequireLoaded()
    {
        if (_loaded)
            return;
 
        if (_loader.loadReference)
            _loader.loadReference();
 
        if (!_loaded)
            throw SqlRequireLoadedError(Reflection::TypeNameOf<std::remove_cvref_t<decltype(*this)>>);
    }
 
    ValueType _referencedFieldValue {};
    Loader _loader {};
    bool _loaded = false;
    bool _modified = false;
    std::unique_ptr<ReferencedRecord> _record {};
};
 
template <auto ReferencedField>
std::ostream& operator<<(std::ostream& os, BelongsTo<ReferencedField> const& belongsTo)
{
    return os << belongsTo.Value();
}
 
namespace detail
{
template <typename T>
struct IsBelongsToType: std::false_type
{
};
 
template <auto ReferencedField, auto ColumnNameOverrideString>
struct IsBelongsToType<BelongsTo<ReferencedField, ColumnNameOverrideString>>: std::true_type
{
};
 
} // namespace detail
 
template <typename T>
constexpr bool IsBelongsTo = detail::IsBelongsToType<std::remove_cvref_t<T>>::value;
 
template <auto ReferencedField, auto ColumnNameOverrideString>
struct SqlDataBinder<BelongsTo<ReferencedField, ColumnNameOverrideString>>
{
    using SelfType = BelongsTo<ReferencedField, ColumnNameOverrideString>;
    using InnerType = typename SelfType::ValueType;
 
    static constexpr auto ColumnType = SqlDataBinder<InnerType>::ColumnType;
 
    static LIGHTWEIGHT_FORCE_INLINE SQLRETURN InputParameter(SQLHSTMT stmt,
                                                             SQLUSMALLINT column,
                                                             SelfType const& value,
                                                             SqlDataBinderCallback& cb)
    {
        return SqlDataBinder<InnerType>::InputParameter(stmt, column, value.Value(), cb);
    }
 
    static LIGHTWEIGHT_FORCE_INLINE SQLRETURN
    OutputColumn(SQLHSTMT stmt, SQLUSMALLINT column, SelfType* result, SQLLEN* indicator, SqlDataBinderCallback& cb)
    {
        auto const sqlReturn = SqlDataBinder<InnerType>::OutputColumn(stmt, column, &result->MutableValue(), indicator, cb);
        cb.PlanPostProcessOutputColumn([result]() { result->SetModified(true); });
        return sqlReturn;
    }
 
    static LIGHTWEIGHT_FORCE_INLINE SQLRETURN GetColumn(
        SQLHSTMT stmt, SQLUSMALLINT column, SelfType* result, SQLLEN* indicator, SqlDataBinderCallback const& cb) noexcept
    {
        auto const sqlReturn = SqlDataBinder<InnerType>::GetColumn(stmt, column, &result->MutableValue(), indicator, cb);
        if (SQL_SUCCEEDED(sqlReturn))
            result->SetModified(true);
        return sqlReturn;
    }
};