** Changed in: mahara
Importance: Undecided => High
** Changed in: mahara
Milestone: None => 21.04.0
** Changed in: mahara
Status: New => In Progress
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https://bugs.launchpad.net/bugs/1898650
Title:
Duplicate Collection View Displayorder
Status in Mahara:
In Progress
Bug description:
Mahara: 19.10.04 ( 2019093018 )
OS: Linux 16.04 (PHP 7.0)
DB: Postgres
Browser: FF / Chrome
In certain situations, the users are able to create a collection where the
displayorder of the pages are duplicated. i.e. 2 pages with displayorder = 0 in
the collection_view table.
I have no idea how this situation came about. I only saw it in one of
our production sites.
For 1 collection with 37 pages, there were:
* 2 pages with displayorder = 0
* 2 pages with displayorder = 1
The remaining pages were ordered correctly starting from 2 onwards.
The result was the error:
'A nonrecoverable error occurred. This probably means you have
encountered a bug in the system'
When trying to go to the Pages and Collections screen.
The offending subquery which returned multiple records for a column is
in lib/view.php::get_myviews_data() line 3804:
$collselect = '
UNION
SELECT (SELECT view FROM {collection_view} cvid WHERE
cvid.collection = c.id AND displayorder = 0) as id,
null AS vid, c.name as title, c.name AS vtitle, c.description,
null as type, c.ctime as vctime, c.mtime as vmtime, c.mtime as vatime,
c.owner, c.group, c.institution, null as locked, null as
ownerformat, null as urlid, null AS vvisits,
(SELECT COUNT(*) FROM {collection_view} cv WHERE
cv.collection = c.id) AS numviews, c.id AS collid';
As a side note, we really should not be calling subqueries for a column. This
has huge performance issues since that subquery will be run for every row.
I also note that there is another subquery to retrieve 'numviews'.
Again, another performance hit.
To eliminate the performance hit, the following should be changed:
$collselect = '
UNION
SELECT cvid.view as id,
null AS vid, c.name as title, c.name AS vtitle, c.description,
null as type, c.ctime as vctime, c.mtime as vmtime, c.mtime as vatime,
c.owner, c.group, c.institution, null as locked, null as
ownerformat, null as urlid, null AS vvisits,
numviews.numviews AS numviews, c.id AS collid';
$collfrom = '
FROM {view} v
LEFT OUTER JOIN {collection_view} cv ON cv.view = v.id
LEFT OUTER JOIN {collection} c ON cv.collection = c.id
INNER join {collection_view} cvid on cvid.collection = c.id AND
cvid.displayorder = 0
INNER JOIN (SELECT COUNT(*) as numviews, numcv.collection
FROM {collection_view} numcv
INNER JOIN {collection} numc ON numcv.collection = numc.id
GROUP BY numcv.collection) as numviews on
numviews.collection = cv.collection';
and under 'mostcomments':
$collgroupby = ' GROUP BY cvid.view, numviews.numviews, c.id';
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