Codeigniter using Join or where to validate a row of result - php

Question

User table:
User_id(Pk,AI) | First_name | Last_name
1 | John | Doe
2 | Peter | Griffin
3 | Donald | Duck
Item table:
Item_id(PK,AI) | Owner(FK - user_id) | Item_name
1 | 1 | Shoes
2 | 2 | Pants
3 | 3 | Shirt
Item_review table:
Item_review_id(PK,AI) | Item(FK - item_id) | Reviewer(FK - user_id) | Rating |
Content
1 | 1 | 2 | 4 | Great
With the Tables above, There are three things i want to check before inserting a row into the review table.
Check if reviewer is not the item owner(cannot review own item or biased review)
Form validation(if reviewer inputted anything into the rating and content)
Check if review exists(no duplicate review or only one review per user)
That's my procedure, I've done the other two except the first one as i am unsure and confused on how to do this.
I could simply use a get where query like:
public function check_biased_review($user_id, $item_id){
$this->db->select('*');
$this->db->from('item');
$this->db->where('item_id', $item_id);
$this->db->where('owner', $user_id);
$query = $this->db->get();
if($query->num_rows() > 0){
return TRUE;}
else{
return FALSE;}
}
I actually solved this by writing the code above, i had this misconception that i would have to query so many rows if there are many reviews to find the matching rows that i forgot about the where clause in the first place which will do it in the db instead of doing it in the model function with an foreach loop and an if statement. I guess you have to code first instead of having assumptions and never doing it to check or you could waste time like i did.
But my first solution was to use a join query. $item_id and $user_id is passed from the controller to the model.
How would i go about joining the tables to get the same result?

Answer 1

I just try to give you an join query example below.
$this->db->select('*');
$this->db->from('Item_review');
$this->db->join('User','Item_review.user_id = User.User_id');
$this->db->join('Item','Item_review.item_id= Item.Item_id');
$this->db->where('item_id', $item_id);
$this->db->where('owner', $user_id);
$query = $this->db->get();