Call to a member function result() on a non-object - php

Question

There is an error message when my view is being loaded. "Call to a member function result() on a non-object"
How do I fix this?
This is the loop in my View: discussion/view.php
<?php foreach ($query->result() as $result) : ?>
<tr>
<td>
<?php echo anchor('comments/index/'.$result->ds_id,$result->ds_title) . ' '
. $this->lang->line('comments_created_by') . $result->usr_name; ?>
<?php echo anchor('discussions/flag/'.$result->ds_id,
$this->lang->line('discussion_flag')) ; ?>
<br />
<?php echo $result->ds_body ; ?>
</td>
</tr>
<?php endforeach ; ?>
and this is the function index in my Comments Controller:
public function index() {
if ($this->input->post()) {
$ds_id = $this->input->post('ds_id');
} else {
$ds_id = $this->uri->segment(3);
}
$page_data['discussion_query'] = $this->Discussions_model->fetch_discussion($ds_id);
$page_data['comment_query'] = $this->Comments_model->fetch_comments($ds_id);
$page_data['ds_id'] = $ds_id;
$this->form_validation->set_rules('ds_id', $this->lang->line('comments_comment_hidden_id'), 'required|min_length[1]|max_length[11]');
$this->form_validation->set_rules('comment_name', $this->lang->line('comments_comment_name'), 'required|min_length[1]|max_length[25]');
$this->form_validation->set_rules('comment_email', $this->lang->line('comments_comment_email'), 'required|min_length[1]|max_length[255]');
$this->form_validation->set_rules('comment_body', $this->lang->line('comments_comment_body'), 'required|min_length[1]|max_length[5000]');
if ($this->form_validation->run() == FALSE) {
$this->load->view('common/header');
$this->load->view('nav/top_nav');
$this->load->view('comments/view', $page_data);
$this->load->view('common/footer');
} else {
$data = array('cm_body' => $this->input->post('comment_body'),
'usr_email' => $this->input->post('comment_email'),
'usr_name' => $this->input->post('comment_name'),
'ds_id' => $this->input->post('ds_id')
);
if ($this->Comments_model->new_comment($data)) {
redirect('comments/index/'.$ds_id);
} else {
// error
$this->data['message'] = 'Error!';
}
}
}