get result count codeigniter

1$this->db
2  ->where(['field'=>'foo'])
3  ->from("tablename")
4  ->count_all_results();
5
6//OR 
7$this->db
8  ->where(['field'=>'foo'])
9  ->count_all_results("tablename");

1$this->db->select('id');
2$this->db->from('table');
3$this->db->where($your_conditions);
4$num_results = $this->db->count_all_results();

1public function record_count() {
2   return $this->db->count_all("tablename");
3}