yf_model_relation class

    public function attach($id, $params = [])
    {
        $relation = $this->_relation;
        $model = $this->_model;
        $db = $model->_db;
        $pivot_table = $relation['pivot_table'];
        $type = $relation['type'];

        if ($type === 'belongs_to_many') {
            return $db->replace($pivot_table, [
                $relation['other_key'] => $id,
                $relation['foreign_key'] => $model->get_key(),
            ]);
        }
        return false;
    }

    public function detach($id, $params = [])
    {
        $relation = $this->_relation;
        $model = $this->_model;
        $db = $model->_db;
        $pivot_table = $relation['pivot_table'];
        $type = $relation['type'];

        if ($type === 'belongs_to_many') {
            return $db->from($pivot_table)
                ->where($relation['other_key'], $id)
                ->where($relation['foreign_key'], $model->get_key())
                ->limit(1)
                ->delete();
        }
        return false;
    }

    public function get_data()
    {
        $relation = $this->_relation;
        $model = $this->_model;
        $db = $model->_db;
        $table = $model->get_table();
        $table_alias = 't0';
        $id = $model->get_key();
        $query = $relation['query'];
        $rel_model = $query->_model;
        $rel_table = $rel_model->get_table();
        $type = $relation['type'];

        if ($type === 'has_one') {
            return $query
                ->whereid($id)
                ->get();
        } elseif ($type === 'has_many') {
            $foreign_key = $relation['foreign_key'];
            $local_key = $relation['local_key'];

            $cols = [];
            foreach ($db->utils()->columns_names($rel_table) as $col) {
                $col = $table_alias . '.' . $col;
                $cols[$col] = $col;
            }
            $join_table = $table;
            $join_alias = 't1';
            return $query
                ->whereid($id)
                ->select(implode(', ', $cols))
                ->inner_join($join_table . ' AS ' . $join_alias, [
                    $table_alias . '.' . $foreign_key => $join_alias . '.' . $local_key,
                ])->get_all();
        } elseif ($type === 'belongs_to') {
            $foreign_key = $relation['foreign_key'];
            $other_key = $relation['other_key'];

            $join_table = $table;
            $join_alias = 't1';

            $cols = [];
            foreach ($db->utils()->columns_names($rel_table) as $col) {
                $col = $table_alias . '.' . $col;
                $cols[$col] = $col;
            }
            return $query
                ->where($join_alias . '.' . $model->get_key_name(), $id)
                ->select(implode(', ', $cols))
                ->inner_join($join_table . ' AS ' . $join_alias, [
                    $table_alias . '.' . $other_key => $join_alias . '.' . $foreign_key,
                ])->get();
        } elseif ($type === 'belongs_to_many') {
            $foreign_key = $relation['foreign_key'];
            $other_key = $relation['other_key'];

            $pivot_table = $db->_fix_table_name($relation['pivot_table']);
            $pivot_alias = 't1';

            $join_table = $table;
            $join_alias = 't2';

            $cols = [];
            foreach ($db->utils()->columns_names($rel_table) as $col) {
                $col = $table_alias . '.' . $col;
                $cols[$col] = $col;
            }
            return $query->whereid($id)
                ->select(implode(', ', $cols))
                ->inner_join($pivot_table . ' AS ' . $pivot_alias, [
                    $table_alias . '.' . $rel_model->get_key_name() => $pivot_alias . '.' . $other_key,
                ])
                ->inner_join($join_table . ' AS ' . $join_alias, [
                    $pivot_alias . '.' . $foreign_key => $join_alias . '.' . $model->get_key_name(),
                ])
                ->get_all();
        } elseif ($type === 'has_many_through') {
            // TODO
        } elseif ($type === 'morph_one') {
            // TODO
        } elseif ($type === 'morph_to') {
            // TODO
        } elseif ($type === 'morph_many') {
            // TODO
        } elseif ($type === 'morph_to_many') {
            // TODO
        } elseif ($type === 'morphed_by_many') {
            // TODO
        }
    }

    public function __construct($relation, $model)
    {
        $this->_relation = $relation;
        $this->_model = $model;
    }

    public function _create_pivot_table($pivot, $relation)
    {
        $r = $relation;
        $model = $this->_model;
        $db = $model->_db;
        $db->utils->create_table($pivot, function ($t) use ($r) {
            $t->int($r['local_key'], ['unsigned' => true, 'nullable' => false]);
            $t->int($r['foreign_key'], ['unsigned' => true, 'nullable' => false]);
            $t->primary([$r['local_key'] => $r['local_key'], $r['foreign_key'] => $r['foreign_key']]);
        });
    }

    public function _get_model()
    {
        return $this->_model;
    }

    public function _get_relation()
    {
        return $this->_relation;
    }