cpphibernate/include/cpphibernate/driver/mariadb/impl/_context.inl

#pragma once



namespace cpphibernate {
namespace mariadb {

    /* base_context */

    base_context::base_context(
        const schema_t&             p_schema,
        ::cppmariadb::connection&   p_connection)
        : schema    (p_schema)
        , connection(p_connection)
        { }

    /* data_context */

    template<typename T_dataset>
    data_context::data_context(
        const schema_t&             p_schema,
        ::cppmariadb::connection&   p_connection,
        T_dataset&                  p_dataset)
        : base_context  (p_schema, p_connection)
        , _dataset_id   (0)
        , _dataset      (nullptr)
        , _table        (nullptr)
        { set(p_dataset); }

    template<typename T_dataset>
    decltype(auto) data_context::get() const
    {
        using dataset_type = mp::decay_t<T_dataset>;

        /* check if tha context has a dataset assigned (should never fail) */
        if (!_dataset)
            throw misc::hibernate_exception("no data assigned!");

        auto dataset_id = misc::get_type_id(hana::type_c<dataset_type>);

        /* if the dataset IDs does not match, search in the base tables for a matching ID */
        if (dataset_id != _dataset_id)
        {
            /* get the table of the stored dataset */
            if (!_table)
                _table = &schema.table(_dataset_id);

            /* check if the table matches the stored dataset (should never happen) */
            else if (_table->dataset_id != _dataset_id)
                throw misc::hibernate_exception("invalid table!");

            /* walk through base tables until we have found a matching ID */
            auto table = _table;
            while(table && table->dataset_id != dataset_id)
                table = table->base_table;

            /* check if we have found a suitable table, if not throw an exception */
            if (!table)
            {
                throw misc::hibernate_exception(utl::type_helper<dataset_type>::name() +
                    " is not a derived type of dataset with id " + std::to_string(_dataset_id));
            }
        }

        /* return the dataset */
        return *static_cast<dataset_type*>(_dataset);
    }

    template<typename T_dataset>
    void data_context::set(T_dataset& dataset)
    {
        _dataset_id = misc::get_type_id(hana::type_c<mp::decay_t<T_dataset>>);
        _dataset    = &dataset;
        _table      = nullptr;
    }



    namespace __impl
    {

        /* change_context_builder */

        template<typename X, typename>
        struct change_context_builder
        {
            template<typename... T_args>
            static constexpr decltype(auto) apply(T_args&&...)
                { static_assert(sizeof...(T_args) == -1, "Invalid parameters for change_context(...)!"); }
        };

        template<typename T_context, typename T_dataset>
        struct change_context_builder<
            mp::list<T_context, T_dataset>,
            mp::enable_if_t<
                mp::is_base_of_v<data_context, mp::decay_t<T_context>>>>
        {
            static constexpr decltype(auto) apply(const T_context& context, T_dataset& dataset)
            {
                auto new_context = context;
                new_context.set(dataset);
                return new_context;
            }
        };

    }

#if 0

    /* read_context */

    template<typename T_dataset>
    T_dataset& read_context
        ::emplace(const table_t* table) const
    {
        using dataset_type = mp::decay_t<T_dataset>;

        // check table
        auto dataset_id = misc::get_type_id(hana::type_c<dataset_type>);
        if (!table)
            table = &schema.table(dataset_id);
        else if (table->dataset_id != dataset_id)
            throw misc::hibernate_exception("wrong table passed!");

        // check base
        auto tbl = table;
        while (tbl && tbl->dataset_id != base_dataset_id)
            tbl = tbl->base_table;
        if (!tbl)
        {
            throw misc::hibernate_exception(utl::type_helper<dataset_type>::name() +
                " is not a derived type of dataset with id " + std::to_string(base_dataset_id));
        }

        // create dataset
        auto ptr  = std::make_unique<dataset_type>();
        auto data = emplace_intern(ptr.get(), dataset_id);
        if (!data)
            throw misc::hibernate_exception("unable to store created dataset in context!");
        ptr.release();
        return *static_cast<dataset_type*>(data);
    }
#endif
} }