Add StudyGroups with ExternalUsers only

db/migrate/20181122084546_create_study_groups.rb

@@ -0,0 +1,13 @@
+class CreateStudyGroups < ActiveRecord::Migration[5.2]
+  def change
+    create_table :study_groups do |t|
+      t.string :name
+      t.string :external_id
+      t.belongs_to :consumer
+      t.timestamps
+    end
+
+    add_index :study_groups, [:external_id, :consumer_id], unique: true
+  end
+end
+

db/migrate/20181122090243_create_study_group_memberships.rb

@@ -0,0 +1,8 @@
+class CreateStudyGroupMemberships < ActiveRecord::Migration[5.2]
+  def change
+    create_table :study_group_memberships do |t|
+      t.belongs_to :study_group
+      t.belongs_to :user, polymorphic: true
+    end
+  end
+end

db/migrate/20181122090244_add_study_group_to_submission.rb

@@ -0,0 +1,5 @@
+class AddStudyGroupToSubmission < ActiveRecord::Migration[5.2]
+  def change
+    add_reference :submissions, :study_group, index: true, null: true, foreign_key: true
+  end
+end