duplicate data avoiding in codeigniter datamapper !? PHP

Question

I am inserting the Food(table) keys/enteries into the DB and I get duplicate keys even though I am not suppose to based on the manual. I am really confused and stuck!? Relationship is as follows: every user has a related to many different food types. Then whenever I read the user's $data['food'] agin...It creates a duplicate entry . Meaning that next time the user logs in instead of knowing that food exits. it increments the primary key and does not understand that the key exits contrary to what manual suggest that save is smart enough to know that...So my problem is I want to have only one copy of every entry but I end up with more entries. How Can I avoid having duplicate entries ?

for(i=0; sizof($data['food']);i++){
   $f=new Food();
   $f->food_id=$food['id'];
   $f->name=$food[$j]['name'];
   $f->user_id=$food_id;                                  
   $u=new User();
   $u->where('user_id',$food)->get();
   //save food and the relationship
   $fm->save($f);
   }

Answer 1

Why did you set your user_id to be the same as food_id?

The code you wrote to get the user details, doesn't seem to be doing anything too.