Error: Call to undefined method CodeIgniter\Database\Postgre\Connection::select() - codeigniter-4

Question

public function getLoad() {
$q = $this->conn->select('load.level_id, load.section_id, sub.subject_title, sub.subject_name')
->from('academics.tbl_teaching_load load')
->join('academics.tbl_subjects sub', 'sub.subject_id = load.subject_id')
->where('user_id', $this->request->getVar('user_id'))
->get()->getResult();
echo json_encode($q);
}
As the title said, it returns an error: Call to undefined method CodeIgniter\Database\Postgre\Connection::select()
I am new too CI4 and trying to join a table. The only problem I encounter so far is this. I can't seem to find the solution for the problem. Any help or tips will do. TYIA

Answer 1

Error:
Call to undefined method CodeIgniter\\Database\\Postgre\\Connection::select()
Explanation:
The error above is pretty clear. You're trying to call the select(...) method which doesn't exist in the CodeIgniter\Database\Postgre\Connection class.
However, the select(...) method exists in the CodeIgniter\Database\BaseBuilder class. You can receive the BaseBuilder instance from the Connection instance through the inherited CodeIgniter\Database\BaseConnection::table(...) method.
In addition, I would recommend you to first join your table(s) before selecting columns using the ->select(...) method. That would be easier to read and interpret.
Hence, reorder and change your query to...
Solution:
public function getLoad()
{
$q = $this->conn->table('academics.tbl_teaching_load load')
->join('academics.tbl_subjects sub', 'sub.subject_id = load.subject_id')
->where('user_id', $this->request->getVar('user_id'))
->select(['load.level_id', 'load.section_id', 'sub.subject_title', 'sub.subject_name'])
->get()->getResult();
echo json_encode($q);
}