improve assignment student visibilities group performance

shouldn't join on every group membership belonging
to the users (even outside of the course)

closes #ADMIN-1112

Change-Id: I87926dfe0e73e9c2b1efc7c2c8b4aae903c02744
Reviewed-on: https://gerrit.instructure.com/153723
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Reviewed-by: Carl Kibler <ckibler@instructure.com>
Tested-by: Jenkins
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>

db/migrate/20180613202631_improve_asv_group_performance.rb

@@ -0,0 +1,120 @@
+class ImproveAsvGroupPerformance < ActiveRecord::Migration[5.1]
+  tag :postdeploy
+
+  def up
+    # find the groups first and then worry about group memberships
+    self.connection.execute %(CREATE OR REPLACE VIEW #{connection.quote_table_name('assignment_student_visibilities')} AS
+    SELECT DISTINCT a.id as assignment_id,
+      e.user_id as user_id,
+      c.id as course_id
+
+      FROM #{Assignment.quoted_table_name} a
+
+      JOIN #{Course.quoted_table_name} c
+        ON a.context_id = c.id
+        AND a.context_type = 'Course'
+
+      JOIN #{Enrollment.quoted_table_name} e
+        ON e.course_id = c.id
+        AND e.type IN ('StudentEnrollment', 'StudentViewEnrollment')
+        AND e.workflow_state NOT IN ('deleted', 'rejected', 'inactive')
+
+      JOIN #{CourseSection.quoted_table_name} cs
+        ON cs.course_id = c.id
+        AND e.course_section_id = cs.id
+
+      LEFT JOIN #{Group.quoted_table_name} g
+        ON g.context_type = 'Course'
+        AND g.context_id = c.id
+        AND g.workflow_state = 'available'
+
+      LEFT JOIN #{GroupMembership.quoted_table_name} gm
+        ON gm.user_id = e.user_id
+        AND gm.workflow_state = 'accepted'
+        AND gm.group_id = g.id
+
+      LEFT JOIN #{AssignmentOverrideStudent.quoted_table_name} aos
+        ON aos.assignment_id = a.id
+        AND aos.user_id = e.user_id
+        AND aos.workflow_state = 'active'
+
+      LEFT JOIN #{AssignmentOverride.quoted_table_name} ao
+        ON ao.assignment_id = a.id
+        AND ao.workflow_state = 'active'
+        AND (
+          (ao.set_type = 'CourseSection' AND ao.set_id = cs.id)
+          OR (ao.set_type = 'ADHOC' AND ao.set_id IS NULL AND ao.id = aos.assignment_override_id)
+          OR (ao.set_type = 'Group' AND ao.set_id = g.id AND gm.id IS NOT NULL)
+        )
+
+      LEFT JOIN #{Submission.quoted_table_name} s
+        ON s.user_id = e.user_id
+        AND s.assignment_id = a.id
+        AND s.workflow_state NOT IN ('deleted', 'unsubmitted')
+
+      WHERE a.workflow_state NOT IN ('deleted','unpublished')
+        AND(
+          ( a.only_visible_to_overrides = 'true' AND (ao.id IS NOT NULL OR s.id IS NOT NULL))
+          OR (COALESCE(a.only_visible_to_overrides, 'false') = 'false')
+        )
+      )
+  end
+
+  def down
+    self.connection.execute %(CREATE OR REPLACE VIEW #{connection.quote_table_name('assignment_student_visibilities')} AS
+    SELECT DISTINCT a.id as assignment_id,
+      e.user_id as user_id,
+      c.id as course_id
+
+      FROM #{Assignment.quoted_table_name} a
+
+      JOIN #{Course.quoted_table_name} c
+        ON a.context_id = c.id
+        AND a.context_type = 'Course'
+
+      JOIN #{Enrollment.quoted_table_name} e
+        ON e.course_id = c.id
+        AND e.type IN ('StudentEnrollment', 'StudentViewEnrollment')
+        AND e.workflow_state NOT IN ('deleted', 'rejected', 'inactive')
+
+      JOIN #{CourseSection.quoted_table_name} cs
+        ON cs.course_id = c.id
+        AND e.course_section_id = cs.id
+
+      LEFT JOIN #{GroupMembership.quoted_table_name} gm
+        ON gm.user_id = e.user_id
+        AND gm.workflow_state = 'accepted'
+
+      LEFT JOIN #{Group.quoted_table_name} g
+        ON g.context_type = 'Course'
+        AND g.context_id = c.id
+        AND g.workflow_state = 'available'
+        AND gm.group_id = g.id
+
+      LEFT JOIN #{AssignmentOverrideStudent.quoted_table_name} aos
+        ON aos.assignment_id = a.id
+        AND aos.user_id = e.user_id
+        AND aos.workflow_state = 'active'
+
+      LEFT JOIN #{AssignmentOverride.quoted_table_name} ao
+        ON ao.assignment_id = a.id
+        AND ao.workflow_state = 'active'
+        AND (
+          (ao.set_type = 'CourseSection' AND ao.set_id = cs.id)
+          OR (ao.set_type = 'ADHOC' AND ao.set_id IS NULL AND ao.id = aos.assignment_override_id)
+          OR (ao.set_type = 'Group' AND ao.set_id = g.id)
+        )
+
+      LEFT JOIN #{Submission.quoted_table_name} s
+        ON s.user_id = e.user_id
+        AND s.assignment_id = a.id
+        AND s.workflow_state NOT IN ('deleted', 'unsubmitted')
+
+      WHERE a.workflow_state NOT IN ('deleted','unpublished')
+        AND(
+          ( a.only_visible_to_overrides = 'true' AND (ao.id IS NOT NULL OR s.id IS NOT NULL))
+          OR (COALESCE(a.only_visible_to_overrides, 'false') = 'false')
+        )
+      )
+  end
+end