diff --git a/app/models/user.rb b/app/models/user.rb
index 8ef3c3ceff0..5a4c373705b 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -109,7 +109,7 @@ class User < ActiveRecord::Base
   has_many :created_projects,         foreign_key: :creator_id, class_name: 'Project'
   has_many :users_star_projects, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
   has_many :starred_projects, through: :users_star_projects, source: :project
-  has_many :project_authorizations
+  has_many :project_authorizations, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
   has_many :authorized_projects, through: :project_authorizations, source: :project
 
   has_many :user_interacted_projects
diff --git a/changelogs/unreleased/ab-43706-composite-primary-keys.yml b/changelogs/unreleased/ab-43706-composite-primary-keys.yml
new file mode 100644
index 00000000000..b17050a64c8
--- /dev/null
+++ b/changelogs/unreleased/ab-43706-composite-primary-keys.yml
@@ -0,0 +1,5 @@
+---
+title: Add NOT NULL constraints to project_authorizations.
+merge_request: 18980
+author:
+type: other
diff --git a/db/migrate/20180517082340_add_not_null_constraints_to_project_authorizations.rb b/db/migrate/20180517082340_add_not_null_constraints_to_project_authorizations.rb
new file mode 100644
index 00000000000..3b7b877232b
--- /dev/null
+++ b/db/migrate/20180517082340_add_not_null_constraints_to_project_authorizations.rb
@@ -0,0 +1,38 @@
+class AddNotNullConstraintsToProjectAuthorizations < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  def up
+    if Gitlab::Database.postgresql?
+      # One-pass version for PostgreSQL
+      execute <<~SQL
+      ALTER TABLE project_authorizations
+        ALTER COLUMN user_id SET NOT NULL,
+        ALTER COLUMN project_id SET NOT NULL,
+        ALTER COLUMN access_level SET NOT NULL
+      SQL
+    else
+      change_column_null :project_authorizations, :user_id, false
+      change_column_null :project_authorizations, :project_id, false
+      change_column_null :project_authorizations, :access_level, false
+    end
+  end
+
+  def down
+    if Gitlab::Database.postgresql?
+      # One-pass version for PostgreSQL
+      execute <<~SQL
+      ALTER TABLE project_authorizations
+        ALTER COLUMN user_id DROP NOT NULL,
+        ALTER COLUMN project_id DROP NOT NULL,
+        ALTER COLUMN access_level DROP NOT NULL
+      SQL
+    else
+      change_column_null :project_authorizations, :user_id, true
+      change_column_null :project_authorizations, :project_id, true
+      change_column_null :project_authorizations, :access_level, true
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index ed29d202f91..c2e97f93160 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180512061621) do
+ActiveRecord::Schema.define(version: 20180517082340) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1449,9 +1449,9 @@ ActiveRecord::Schema.define(version: 20180512061621) do
   add_index "personal_access_tokens", ["user_id"], name: "index_personal_access_tokens_on_user_id", using: :btree
 
   create_table "project_authorizations", id: false, force: :cascade do |t|
-    t.integer "user_id"
-    t.integer "project_id"
-    t.integer "access_level"
+    t.integer "user_id", null: false
+    t.integer "project_id", null: false
+    t.integer "access_level", null: false
   end
 
   add_index "project_authorizations", ["project_id"], name: "index_project_authorizations_on_project_id", using: :btree