如何用爆炸选择多个选择

Question

所以，我有$dp->isi = "1,2,3,4"

<select name="isi[]" class="form-control select2" multiple="multiple" data-placeholder="Choose"
                    style="width: 100%;">
                <?php foreach ($data->result() as $db) : ?>
                <option value="<?php echo $db->id;?>"
                <?php if ($db->id == explode(',',$dp->isi)) { ?>
                selected="selected"<?php } ?>>
                <?php echo $db->name; ?>
                </option>
                <?php endforeach; ?>
            </select>

使用codeIgniter，我希望在multiselect上选择$dp->isi值。