add selection table for moderated grading

closes: CNVS-22001

test plan:
1. run migrations
2. the table moderated_grading_selection should exist with the following columns:
  - assignment_id
  - student_id
  - selected_provisional_grade_id
3. in rails console, the class (model) ModeratedGrading::Selection should exist.

Change-Id: I137ad648e044d00cc9ba426d327f6cc91982e2b8
Reviewed-on: https://gerrit.instructure.com/63027
Tested-by: Jenkins
QA-Review: Clare Strong <clare@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>

Author: djbender

app/models/assignment.rb

@@ -75,6 +75,7 @@ class Assignment < ActiveRecord::Base
   has_one :rubric, :through => :rubric_association
   has_one :teacher_enrollment, class_name: 'TeacherEnrollment', foreign_key: 'course_id', primary_key: 'context_id', preload: :user, conditions: ["enrollments.workflow_state = 'active' AND enrollments.type = 'TeacherEnrollment'"]
   has_many :ignores, :as => :asset
+  has_many :moderated_grading_selections, class_name: 'ModeratedGrading::Selection'
   belongs_to :context, :polymorphic => true
   validates_inclusion_of :context_type, :allow_nil => true, :in => ['Course']
   validates_length_of :title, :maximum => maximum_string_length, :allow_nil => false, :allow_blank => true

app/models/moderated_grading/provisional_grade.rb

@@ -7,7 +7,10 @@ class ModeratedGrading::ProvisionalGrade < ActiveRecord::Base
   belongs_to :submission
   belongs_to :scorer, class_name: 'User'
 
-  has_many :rubric_assessments, :as => :artifact
+  has_many :rubric_assessments, as: :artifact
+  has_one :selection,
+    class_name: 'ModeratedGrading::Selection',
+    foreign_key: :selected_provisional_grade_id
 
   validates :scorer, presence: true
   validates :submission, presence: true

app/models/moderated_grading/selection.rb

@@ -0,0 +1,7 @@
+class ModeratedGrading::Selection < ActiveRecord::Base
+  belongs_to :provisional_grade,
+    foreign_key: :selected_provisional_grade_id,
+    class_name: 'ModeratedGrading::ProvisionalGrade'
+  belongs_to :assignment
+  belongs_to :student, class_name: 'User'
+end

app/models/user.rb

@@ -143,8 +143,10 @@ def self.enrollment_conditions(state)
   has_many :sis_post_grades_statuses
   has_many :content_migrations, :as => :context
   has_many :content_exports, :as => :context
-  has_many :usage_rights, as: :context, class_name: 'UsageRights', dependent: :destroy
-
+  has_many :usage_rights,
+    as: :context,
+    class_name: 'UsageRights',
+    dependent: :destroy
   has_many :gradebook_csvs, dependent: :destroy
 
   has_one :profile, :class_name => 'UserProfile'

db/migrate/20150910205710_create_selection_table.rb

@@ -0,0 +1,26 @@
+class CreateSelectionTable < ActiveRecord::Migration
+  tag :predeploy
+
+  def up
+    create_table :moderated_grading_selections do |t|
+      t.integer :assignment_id,                 limit: 8, null: false
+      t.integer :student_id,                    limit: 8, null: false
+      t.integer :selected_provisional_grade_id, limit: 8, null: true
+
+      t.timestamps null: false
+    end
+
+    add_index :moderated_grading_selections, :assignment_id
+    add_index :moderated_grading_selections,
+              [:assignment_id, :student_id],
+              unique: true,
+              name: :idx_mg_selections_unique_on_assignment_and_student
+    add_foreign_key :moderated_grading_selections, :assignments
+    add_foreign_key :moderated_grading_selections, :users, column: :student_id
+    add_foreign_key :moderated_grading_selections, :moderated_grading_provisional_grades, column: :selected_provisional_grade_id
+  end
+
+  def down
+    drop_table :moderated_grading_selections
+  end
+end

spec/models/moderated_grading/provisional_grade_spec.rb

@@ -14,20 +14,30 @@
   let(:now) { Time.zone.now }
 
   it { is_expected.to be_valid }
+
+  it do
+    is_expected.to have_one(:selection).
+      with_foreign_key(:selected_provisional_grade_id).
+      class_name('ModeratedGrading::Selection')
+  end
+  it { is_expected.to belong_to(:submission) }
+  it { is_expected.to belong_to(:scorer).class_name('User') }
+  it { is_expected.to have_many(:rubric_assessments) }
+
   it { is_expected.to validate_presence_of(:scorer) }
   it { is_expected.to validate_presence_of(:submission) }
 
   describe 'grade_attributes' do
     it "returns the proper format" do
       json = provisional_grade.grade_attributes
       expect(json).to eq({
-                           'provisional_grade_id' => provisional_grade.id,
-                           'grade' => 'A',
-                           'score' => 100.0,
-                           'graded_at' => nil,
-                           'scorer_id' => provisional_grade.scorer_id,
-                           'grade_matches_current_submission' => true
-                         })
+        'provisional_grade_id' => provisional_grade.id,
+        'grade' => 'A',
+        'score' => 100.0,
+        'graded_at' => nil,
+        'scorer_id' => provisional_grade.scorer_id,
+        'grade_matches_current_submission' => true
+      })
     end
   end
 
@@ -109,8 +119,8 @@
       pg = sub.find_or_create_provisional_grade! scorer: user, score: 1
 
       prov_assmt = association.assess(:user => student, :assessor => user, :artifact => pg,
-        :assessment => { :assessment_type => 'grading',
-          :"criterion_#{@rubric.criteria_object.first.id}" => { :points => 3, :comments => "good 4 u" } })
+                                      :assessment => { :assessment_type => 'grading',
+                                                       :"criterion_#{@rubric.criteria_object.first.id}" => { :points => 3, :comments => "good 4 u" } })
 
       expect(prov_assmt.score).to eq 3
 
@@ -174,13 +184,13 @@
   describe 'grade_attributes' do
     it "returns the proper format" do
       expect(ModeratedGrading::NullProvisionalGrade.new(1).grade_attributes).to eq({
-          'provisional_grade_id' => nil,
-          'grade' => nil,
-          'score' => nil,
-          'graded_at' => nil,
-          'scorer_id' => 1,
-          'grade_matches_current_submission' => true
-        })
+        'provisional_grade_id' => nil,
+        'grade' => nil,
+        'score' => nil,
+        'graded_at' => nil,
+        'scorer_id' => 1,
+        'grade_matches_current_submission' => true
+      })
     end
   end
-end
+end

spec/models/moderated_grading/selection_spec.rb

@@ -0,0 +1,27 @@
+require 'spec_helper'
+
+describe ModeratedGrading::Selection do
+  it { is_expected.to belong_to(:assignment) }
+
+  it do
+    is_expected.to belong_to(:provisional_grade).
+      with_foreign_key(:selected_provisional_grade_id).
+      class_name('ModeratedGrading::ProvisionalGrade')
+  end
+
+  it do
+    is_expected.to belong_to(:student).
+      class_name('User')
+  end
+
+  it "is restricted to one selection per assignment/student pair" do
+    course_with_student
+    @assignment = @course.assignments.create!
+    s = @assignment.moderated_grading_selections.build
+    s.student_id = @student.id
+    s.save!
+    s2 = @assignment.moderated_grading_selections.build
+    s2.student_id = @student.id
+    expect { s2.save! }.to raise_error(ActiveRecord::RecordNotUnique)
+  end
+end