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[Mahara Bot <1827445@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://reviews.mahara.org/10287
Committed: https://git.mahara.org/mahara/mahara/commit/6a26a0c72f6e595187a86befc5418c33276ee5ef
Submitter: Cecilia Vela Gurovic (ceciliavg@xxxxxxxxxxxxxxx)
Branch:    master

commit 6a26a0c72f6e595187a86befc5418c33276ee5ef
Author: Robert Lyon <robertl@xxxxxxxxxxxxxxx>
Date:   Wed Sep 4 13:15:41 2019 +1200

Bug 1827445: Check if a table exists in a quicker way

Without needing to include the lib/ddl.php file, and create
the xmldb table objects

We do this by trying to query the table to return one value
and capture the SQLException if it doesn't exist

The places changed are where we don't manipulate the table - so have
left upgrade places the same as we will need to do things the ddl.php
way anyway

behatnotneeded

Change-Id: Ic38cee95a221a22e644370b308356cf687a1e831
Signed-off-by: Robert Lyon <robertl@xxxxxxxxxxxxxxx>

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https://bugs.launchpad.net/bugs/1827445

Title:
  Improve efficiency when checking if a table field exists

Status in Mahara:
  Fix Committed

Bug description:
  When upgrading we use a field_exists() check to see if a table has a
  certain column or not which is fine there as upgrade chunks are a one-
  time execution run when users are all logged out.

  However we have begun to use field_exists() within other parts of the
  code and so this can get called on every page load by multiple users
  at once. This requires fetching the ddl.lib file and setting ul an
  XMLDB table object and an XMLDB field object which has overhead.

  Instead we should just query the database directly and ask it if the
  table has the column or not

  So instead of doing:

  require_once('ddl.php');
  $table = new XMLDBTable('tablename');
  $field = new XMLDBField('fieldname');
  if (field_exists($table, $field)) {
      ...
  }

  We could just do:

  if (column_exists('tablename', 'fieldname')) {
      ...
  }

  And have the column_exists function that call the database directly

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