add body to submission draft in graphql

we need to add a 'body' field to the submission draft type
in graphql to allow us to store text entry drafts going forward.

Test Plan:
* run the db migration to add body to submission draft:
** bundle exec rake db:migrate:up VERSION=20190801215707

* create an assignment as a teacher
* add a student to that assignment
* run the following in the /graphiql endpoint to locate the
  submissions for that assignment

  ```query MyQuery {
  assignment(id: "1") {
    submissionsConnection(filter: {states: [unsubmitted, submitted, graded, pending_review]}) {
      nodes {
        _id
        submissionDraft {
          body
        }
      }
    }
  }
}```

** you should see a submission with a null submission draft

* in the rails console, you will need to add a submission
  draft with a body to that submission
** sub = Submission.find(1) // or whatever your submission ID is
** draft = SubmissionDraft.create!(submission: sub,
   submission_attempt = sub.attempt + 1)
** draft.body = 'some text'
** draft.save!
** sub.submission_drafts = [draft]
** sub.save!

* run the query in graphql again, and you should see something
  like:

```
{
  "data": {
    "assignment": {
      "submissionsConnection": {
        "nodes": [
          {
            "_id": "31",
            "submissionDraft": {
              "body": "some text"
            }
          }
        ]
      }
    }
  }
}
```

fixes COMMS-2263

Change-Id: I62877ac43727f02191c84a98e2609bd8f9987733
Reviewed-on: https://gerrit.instructure.com/203674
Reviewed-by: Steven Burnett <sburnett@instructure.com>
Reviewed-by: Landon Gilbert-Bland <lbland@instructure.com>
Reviewed-by: Cameron Matheson <cameron@instructure.com>
Tested-by: Jenkins
QA-Review: Matthew Lemon <mlemon@instructure.com>
Product-Review: Ryan Norton <rnorton@instructure.com>

app/graphql/loaders/api_content_attachment_loader.rb

@@ -0,0 +1,28 @@
+#
+# Copyright (C) 2019 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+class Loaders::ApiContentAttachmentLoader < GraphQL::Batch::Loader
+  def initialize(context)
+    @context = context
+  end
+
+  def perform(htmls)
+    as = Api.api_bulk_load_user_content_attachments(htmls, @context)
+    htmls.each { |html| fulfill(html, as) }
+  end
+end

app/graphql/types/assignment_type.rb

@@ -264,17 +264,6 @@ module Types
       )
     end
 
-    class AttachmentPreloader < GraphQL::Batch::Loader
-      def initialize(context)
-        @context = context
-      end
-
-      def perform(htmls)
-        as = Api.api_bulk_load_user_content_attachments(htmls, @context)
-        htmls.each { |html| fulfill(html, as) }
-      end
-    end
-
     field :description, String, null: true
     def description
       return nil if assignment.description.blank?
@@ -282,8 +271,7 @@ module Types
       load_locked_for do |lock_info|
         # some (but not all) locked assignments allow viewing the description
         next nil if lock_info && !assignment.include_description?(current_user, lock_info)
-        AttachmentPreloader.for(assignment.context).load(assignment.description).then do |preloaded_attachments|
-
+        Loaders::ApiContentAttachmentLoader.for(assignment.context).load(assignment.description).then do |preloaded_attachments|
             GraphQLHelpers::UserContent.process(assignment.description,
                                                 request: context[:request],
                                                 context: assignment.context,

app/graphql/types/submission_draft_type.rb

@@ -22,11 +22,31 @@ module Types
 
     field :_id, ID, 'legacy canvas id', null: false, method: :id
 
-    field :submission_attempt, Integer, null: false
-
     field :attachments, [Types::FileType], null: true
     def attachments
       load_association(:attachments)
     end
+
+    field :body, String, null: true
+    def body
+      load_association(:submission).then do |submission|
+        Loaders::AssociationLoader.for(Submission, :assignment).load(submission).then do |assignment|
+          Loaders::AssociationLoader.for(Assignment, :context).load(assignment).then do
+            Loaders::ApiContentAttachmentLoader.for(assignment.context).load(object.body).then do |preloaded_attachments|
+              GraphQLHelpers::UserContent.process(
+                object.body,
+                context: assignment.context,
+                in_app: context[:in_app],
+                request: context[:request],
+                preloaded_attachments: preloaded_attachments,
+                user: current_user
+              )
+            end
+          end
+        end
+      end
+    end
+
+    field :submission_attempt, Integer, null: false
   end
 end

app/jsx/assignments_2/student/graphqlData/SubmissionDraft.js

@@ -26,18 +26,21 @@ export const SubmissionDraft = {
       attachments {
         ...SubmissionDraftFile
       }
+      body
     }
     ${SubmissionDraftFile.fragment}
   `,
 
   shape: shape({
     _id: string,
-    attachments: arrayOf(SubmissionDraftFile.shape)
+    attachments: arrayOf(SubmissionDraftFile.shape),
+    body: string
   })
 }
 
 export const SubmissionDraftDefaultMocks = {
   SubmissionDraft: () => ({
-    attachments: () => []
+    attachments: () => [],
+    body: null
   })
 }

app/models/submission_draft.rb

@@ -24,6 +24,7 @@ class SubmissionDraft < ActiveRecord::Base
   validates :submission, presence: true
   validates :submission_attempt, numericality: { only_integer: true }
   validates :submission, uniqueness: { scope: :submission_attempt }
+  validates :body, length: {maximum: maximum_text_length, allow_nil: true, allow_blank: true}
   validate :submission_attempt_matches_submission
 
   def submission_attempt_matches_submission

db/migrate/20190801215707_add_body_to_submission_draft.rb

@@ -0,0 +1,25 @@
+#
+# Copyright (C) 2019 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+class AddBodyToSubmissionDraft < ActiveRecord::Migration[5.1]
+  tag :predeploy
+
+  def change
+    add_column :submission_drafts, :body, :text
+  end
+end

schema.graphql

@@ -2535,6 +2535,7 @@ type SubmissionDraft {
   """
   _id: ID!
   attachments: [File!]
+  body: String
   submissionAttempt: Int!
 }
 

spec/graphql/types/submission_draft_type_spec.rb

@@ -29,7 +29,7 @@ RSpec.describe Types::SubmissionDraftType do
   end
 
   def resolve_submission_draft
-    result = CanvasSchema.execute(<<~GQL, context: {current_user: @teacher})
+    result = CanvasSchema.execute(<<~GQL, context: {current_user: @teacher, request: ActionDispatch::TestRequest.create})
       query {
         assignment(id: "#{@assignment.id}") {
           submissionsConnection(filter: {states: [unsubmitted, graded, pending_review, submitted]}) {
@@ -40,6 +40,7 @@ RSpec.describe Types::SubmissionDraftType do
                   _id
                   displayName
                 }
+                body
                 submissionAttempt
               }
             }
@@ -70,4 +71,12 @@ RSpec.describe Types::SubmissionDraftType do
     submission_draft = resolve_submission_draft
     expect(submission_draft['attachments'].first['displayName']).to eq(attachment.display_name)
   end
+
+  it 'returns the draft body' do
+    @submission_draft.body = 'some text'
+    @submission_draft.save!
+
+    submission_draft = resolve_submission_draft
+    expect(submission_draft['body']).to eq('some text')
+  end
 end