From 51e53b9f40bae27a96c0cc193a2ea6a28cb47b91 Mon Sep 17 00:00:00 2001
From: Andrew Nicols <andrew@nicols.co.uk>
Date: Thu, 10 May 2018 15:36:58 +0800
Subject: [PATCH] MDL-61905 mod_workshop: Adjust privacy SQL queries

This change moves the content of WHERE to the JOIN, thus filtering the
results before they are returned. This reduces the number of joined rows
which gives a big performance benefit.
---
 mod/workshop/classes/privacy/provider.php | 39 +++++++++++------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/mod/workshop/classes/privacy/provider.php b/mod/workshop/classes/privacy/provider.php
index 3a073abf87d..ed4eb6dd921 100644
--- a/mod/workshop/classes/privacy/provider.php
+++ b/mod/workshop/classes/privacy/provider.php
@@ -129,20 +129,22 @@ class provider implements
     public static function get_contexts_for_userid(int $userid) : contextlist {
 
         $contextlist = new contextlist();
-
         $sql = "SELECT ctx.id
                   FROM {course_modules} cm
                   JOIN {modules} m ON cm.module = m.id AND m.name = :module
                   JOIN {context} ctx ON ctx.contextlevel = :contextlevel AND ctx.instanceid = cm.id
                   JOIN {workshop} w ON cm.instance = w.id
              LEFT JOIN {workshop_submissions} ws ON ws.workshopid = w.id
-             LEFT JOIN {workshop_assessments} wa ON wa.submissionid = ws.id
-             LEFT JOIN {workshop_aggregations} wr ON wr.workshopid = w.id
+             LEFT JOIN {workshop_assessments} wa ON wa.submissionid = ws.id AND (
+                    wa.reviewerid = :wareviewerid
+                        OR
+                    wa.gradinggradeoverby = :wagradinggradeoverby
+                )
+             LEFT JOIN {workshop_aggregations} wr ON wr.workshopid = w.id AND wr.userid = :wruserid
                  WHERE ws.authorid = :wsauthorid
                     OR ws.gradeoverby = :wsgradeoverby
-                    OR wa.reviewerid = :wareviewerid
-                    OR wa.gradinggradeoverby = :wagradinggradeoverby
-                    OR wr.userid = :wruserid";
+                    OR wa.id IS NOT NULL
+                    OR wr.id IS NOT NULL";
 
         $params = [
             'module' => 'workshop',
@@ -306,9 +308,8 @@ class provider implements
                   JOIN {modules} m ON cm.module = m.id AND m.name = :module
                   JOIN {context} ctx ON ctx.contextlevel = :contextlevel AND ctx.instanceid = cm.id
                   JOIN {workshop} w ON cm.instance = w.id
-                  JOIN {workshop_submissions} ws ON ws.workshopid = w.id
-                 WHERE ctx.id {$contextsql}
-                       AND ws.authorid = :authorid";
+                  JOIN {workshop_submissions} ws ON ws.workshopid = w.id AND ws.authorid = :authorid
+                 WHERE ctx.id {$contextsql}";
 
         $params = $contextparams + [
             'module' => 'workshop',
@@ -418,9 +419,8 @@ class provider implements
                   JOIN {context} ctx ON cm.id = ctx.instanceid AND ctx.contextlevel = :contextlevel
                   JOIN {workshop} w ON cm.instance = w.id
                   JOIN {workshop_submissions} ws ON ws.workshopid = w.id
-                  JOIN {workshop_assessments} wa ON wa.submissionid = ws.id
-                 WHERE ctx.id {$contextsql}
-                       AND wa.reviewerid = :reviewerid";
+                  JOIN {workshop_assessments} wa ON wa.submissionid = ws.id AND wa.reviewerid = :reviewerid
+                 WHERE ctx.id {$contextsql}";
 
         $params = $contextparams + [
             'module' => 'workshop',
@@ -570,9 +570,8 @@ class provider implements
                   JOIN {modules} m ON cm.module = m.id AND m.name = :module
                   JOIN {context} ctx ON ctx.contextlevel = :contextlevel AND ctx.instanceid = cm.id
                   JOIN {workshop} w ON cm.instance = w.id
-                  JOIN {workshop_submissions} ws ON ws.workshopid = w.id
-                 WHERE ctx.id {$contextsql}
-                       AND ws.authorid = :authorid";
+                  JOIN {workshop_submissions} ws ON ws.workshopid = w.id AND ws.authorid = :authorid
+                 WHERE ctx.id {$contextsql}";
 
         $params = $contextparams + [
             'module' => 'workshop',
@@ -607,10 +606,9 @@ class provider implements
                   JOIN {modules} m ON cm.module = m.id AND m.name = :module
                   JOIN {context} ctx ON cm.id = ctx.instanceid AND ctx.contextlevel = :contextlevel
                   JOIN {workshop} w ON cm.instance = w.id
-                  JOIN {workshop_submissions} ws ON ws.workshopid = w.id
+                  JOIN {workshop_submissions} ws ON ws.workshopid = w.id AND ws.authorid = :authorid
                   JOIN {workshop_assessments} wa ON wa.submissionid = ws.id
-                 WHERE ctx.id {$contextsql}
-                       AND ws.authorid = :authorid";
+                 WHERE ctx.id {$contextsql}";
 
         $params = $contextparams + [
             'module' => 'workshop',
@@ -642,9 +640,8 @@ class provider implements
                   JOIN {context} ctx ON cm.id = ctx.instanceid AND ctx.contextlevel = :contextlevel
                   JOIN {workshop} w ON cm.instance = w.id
                   JOIN {workshop_submissions} ws ON ws.workshopid = w.id
-                  JOIN {workshop_assessments} wa ON wa.submissionid = ws.id
-                 WHERE ctx.id {$contextsql}
-                       AND wa.reviewerid = :reviewerid";
+                  JOIN {workshop_assessments} wa ON wa.submissionid = ws.id AND wa.reviewerid = :reviewerid
+                 WHERE ctx.id {$contextsql}";
 
         $params = $contextparams + [
             'module' => 'workshop',