Question

I am getting errors saying $id1 and $id2 are undefined. Am I not accessing them right? If not how do I access them correctly?

$query = $this->db->query("SELECT * FROM churchMembers");
$row = $query->row();
    if ($query->num_rows() != 0) {
      if ($postingUserId == $row->cMuserId) { // check to see what church the posting user is a member of
        $id1 = $row->cMchurchId; // if posting user is a member of a church set it to var id1
      } 
      if ($userid == $row->cMuserId) { // check to see what church myuserid is a member of
        $id2 = $row->cMchurchId; // if myuserid is a member of a church set it to var2
      } 
      if ($id1 == $id2) { // if posting user and myuserid are a member of the same church process the following
        echo json_encode(array('loggedIn' => true, 'isMembershipSame' => true));
      } 
      elseif ($id1 != $id2) { // if posting user and myuserid are not a member of the same user process the following
        echo json_encode(array('loggedIn' => true, 'isMembershipSame' => false));
      }
    }

Answer 1

You don’t define either $id1 or $id2 unless their corresponding if conditions are met, so if either of the preceding conditions is false and doesn’t run, neither variable exists when you attempt to compare them in if ($id1 == $id2).

You should initialize them to empty strings before entering your if chain. Then when you compare them, also verify that they are non-empty:

// ADDENDUM after comments:
// If you put this into a loop to fetch rows,
// the following must be INSIDE the loop to reinitialize
// the two vars on each iteration.

// Initialize them as empty strings
$id1 = "";
$id2 = "";

// If you are in a loop, you should check num_rows() once outside the loop, rather than inside
if ($query->num_rows() != 0) {
  if ($postingUserId == $row->cMuserId) {
    $id1 = $row->cMchurchId;
  } 
  if ($userid == $row->cMuserId) {
    $id2 = $row->cMchurchId;
  } 
  // Test if they are non-empty (conditions matched above) and equal:
  if (!empty($id1) && !empty($id2) && $id1 == $id2) {
    echo json_encode(array('loggedIn' => true, 'isMembershipSame' => true));
  } 
  // No need for else if here, just a plain else clause
  else {
    echo json_encode(array('loggedIn' => true, 'isMembershipSame' => false));
  }
}