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[Mahara Bot <1827445@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://reviews.mahara.org/9950
Committed: https://git.mahara.org/mahara/mahara/commit/3e0cd370e245bd0eb011667430f30df6ab42c4f9
Submitter: Cecilia Vela Gurovic (ceciliavg@xxxxxxxxxxxxxxx)
Branch:    master

commit 3e0cd370e245bd0eb011667430f30df6ab42c4f9
Author: Robert Lyon <robertl@xxxxxxxxxxxxxxx>
Date:   Fri May 3 10:14:51 2019 +1200

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

Without needing to create the xmldb table / field objects

We do this by trying to query the column and capture the SQLException
if it doesn't exist

behatnotneeded

Change-Id: I0a15dd4d1d4e47e6650576c084ee9e1d36b4ae62
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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