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accesslib: get_user_courses_bycap() is less of a piggy now...

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get_user_courses_bycap() replaces get_courses_bycap_fromsess().

Using a combination of in-DB enrolments and in-session capability
checks, we narrow down the courses we fetch from the DB for checking.

This patch adds a small DB query, and has has a moderate impact on
the timings observable on my laptop (~300ms?), but reduces
*significantly* the bandwidth used, which in cluster environments
with frontends separate from backends has a serious impact.
This commit is contained in:
martinlanghoff 2007-09-19 07:04:23 +00:00
parent aeb3916b7a
commit 573674bf47
2 changed files with 94 additions and 22 deletions
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106
lib/accesslib.php
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@ -637,8 +637,8 @@ function has_capability_including_child_contexts($context, $capabilitynames) {
/*
* Get an array of courses (with magic extra bits)
* where the access sess data shows that the cap
* requested is available.
* where the access sess data and in DB enrolments show
* that the cap requested is available.
*
* The main use is for get_my_courses().
*
@ -651,10 +651,24 @@ function has_capability_including_child_contexts($context, $capabilitynames) {
* - the course records have $c->context which is a fully
* valid context object. Saves you a query per course!
*
* - current implementation is _extremely_ stupid but
* works fast enough. We can surely do much MUCH better
* for the common cases, and leave the brute-force to
* "not-easy-to-narrow-down" cases.
* - current implementation is split in -
*
* - if the user has the cap systemwide, stupidly
* grab *every* course for a capcheck. This eats
* a TON of bandwidth, specially on large sites
* with separate DBs...
*
* - otherwise, fetch "likely" courses with a wide net
* that should get us _cheaply_ at least the courses we need, and some
* we won't - we get courses that...
* - are in a category where user has the cap
* - or where use has a role-assignment (any kind)
* - or where the course has an override on for this cap
*
* - walk the courses recordset checking the caps oneach one
* the checks are all in memory and quite fast
* (though we could implement a specialised variant of the
* has_cap_fromsess() code to speed it up)
*
* @param string $capability - name of the capability
* @param array $sess - access session array
@ -665,7 +679,7 @@ function has_capability_including_child_contexts($context, $capabilitynames) {
* @return array $courses - ordered array of course objects - see notes above
*
*/
function get_courses_bycap_fromsess($cap, $sess, $doanything, $sort='c.sortorder ASC', $fields=NULL, $limit=0) {
function get_user_courses_bycap($userid, $cap, $sess, $doanything, $sort='c.sortorder ASC', $fields=NULL, $limit=0) {
global $CFG;
@ -684,19 +698,77 @@ function get_courses_bycap_fromsess($cap, $sess, $doanything, $sort='c.sortorder
} else {
$fields = $basefields;
}
$coursefields = 'c.' .join(',c.', $fields);
$sql = "SELECT $coursefields,
ctx.id AS ctxid, ctx.path AS ctxpath, ctx.depth as ctxdepth
FROM {$CFG->prefix}course c
JOIN {$CFG->prefix}context ctx
ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
ORDER BY $sort;
";
$sysctx = get_context_instance(CONTEXT_SYSTEM);
if (has_cap_fromsess($cap, $sysctx, $sess, $doanything)) {
//
// Apparently the user has the cap sitewide, so walk *every* course
// (the cap checks are moderately fast, but this moves massive bandwidth w the db)
// Yuck.
//
$sql = "SELECT $coursefields,
ctx.id AS ctxid, ctx.path AS ctxpath, ctx.depth as ctxdepth
FROM {$CFG->prefix}course c
JOIN {$CFG->prefix}context ctx
ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
ORDER BY $sort;
";
$rs = get_recordset_sql($sql);
} else {
//
// narrow down where we have the caps to a few contexts
// this will be a combination of
// - categories where we have the rights
// - courses where we have an explicit enrolment OR that have an override
//
$sql = "SELECT ctx.*
FROM {$CFG->prefix}context ctx
WHERE ctx.contextlevel=".CONTEXT_COURSECAT."
ORDER BY ctx.depth";
$rs = get_recordset_sql($sql);
$catpaths = array();
if ($rs->RecordCount()) {
while ($catctx = rs_fetch_next_record($rs)) {
if ($catctx->path != ''
&& has_cap_fromsess($cap, $catctx, $sess, $doanything)) {
$catpaths[] = $catctx->path;
}
}
}
rs_close($rs);
$catclause = '';
if (count($catpaths)) {
$cc = count($catpaths);
for ($n=0;$n<$cc;$n++) {
$catpaths[$n] = "ctx.path LIKE '{$catpaths[$n]}/%'";
}
$catclause = 'OR (' . join(' OR ', $catpaths) .')';
}
unset($catpaths);
//
// Note here that we *have* to have the compound clauses
// in the LEFT OUTER JOIN condition for them to return NULL
// appropriately and narrow things down...
//
$sql = "SELECT $coursefields,
ctx.id AS ctxid, ctx.path AS ctxpath, ctx.depth as ctxdepth
FROM {$CFG->prefix}course c
JOIN {$CFG->prefix}context ctx
ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
LEFT OUTER JOIN {$CFG->prefix}role_assignments ra
ON (ra.contextid=ctx.id AND ra.userid=$userid)
LEFT OUTER JOIN {$CFG->prefix}role_capabilities rc
ON (rc.contextid=ctx.id AND rc.capability='$cap')
WHERE ra.id IS NOT NULL
OR rc.id IS NOT NULL
$catclause
ORDER BY $sort;
";
$rs = get_recordset_sql($sql);
}
$courses = array();
$cc = 0; // keep count
$rs = get_recordset_sql($sql);
if ($rs->RecordCount()) {
while ($c = rs_fetch_next_record($rs)) {
// build the context obj