Remove redundant WHERE from event queriesevents-redundant-where

The default scope in Event would add a "WHERE author_id IS NOT NULL"
clause to every query. Now that "events.author_id" has a NOT NULL clause
set this filter is redundant and we can safely remove it.

In this commit we also add a validation on events.author_id (previously
only defined in PushEvent) just in case something tries to create data
without an author ID. This way we can present a nicer error message
compared to PostgreSQL's foreign key error messages.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/38129

3 files changed, 12 insertions, 7 deletions

diff --git a/app/models/event.rb b/app/models/event.rb
index 0b1f053a7e6..0997b056c6a 100644
--- a/app/models/event.rb
+++ b/app/models/event.rb
@@ -1,7 +1,7 @@
 class Event < ActiveRecord::Base
   include Sortable
   include IgnorableColumn
-  default_scope { reorder(nil).where.not(author_id: nil) }
+  default_scope { reorder(nil) }
 
   CREATED   = 1
   UPDATED   = 2
@@ -77,6 +77,12 @@ class Event < ActiveRecord::Base
 
   scope :for_milestone_id, ->(milestone_id) { where(target_type: "Milestone", target_id: milestone_id) }
 
+  # Authors are required as they're used to display who pushed data.
+  #
+  # We're just validating the presence of the ID here as foreign key constraints
+  # should ensure the ID points to a valid user.
+  validates :author_id, presence: true
+
   self.inheritance_column = 'action'
 
   # "data" will be removed in 10.0 but it may be possible that JOINs happen that
diff --git a/app/models/push_event.rb b/app/models/push_event.rb
index 708513c7861..83ce9014094 100644
--- a/app/models/push_event.rb
+++ b/app/models/push_event.rb
@@ -3,12 +3,6 @@ class PushEvent < Event
   # different "action" value.
   validate :validate_push_action
 
-  # Authors are required as they're used to display who pushed data.
-  #
-  # We're just validating the presence of the ID here as foreign key constraints
-  # should ensure the ID points to a valid user.
-  validates :author_id, presence: true
-
   # The project is required to build links to commits, commit ranges, etc.
   #
   # We're just validating the presence of the ID here as foreign key constraints
diff --git a/changelogs/unreleased/events-redundant-where.yml b/changelogs/unreleased/events-redundant-where.yml
new file mode 100644
index 00000000000..a118a2e33e1
--- /dev/null
+++ b/changelogs/unreleased/events-redundant-where.yml
@@ -0,0 +1,5 @@
+---
+title: Remove redundant WHERE from event queries
+merge_request:
+author:
+type: other