Handle cache in student submission without mutating it

client/cypress/fixtures/module.minimal.js

@@ -6,7 +6,7 @@ export default {
   intro: 'intro',
   assignments: {},
   objectiveGroups: [],
-  id: '',
+  id: 'TW9kdWxlTm9kZToxMjM=',
   chapters: [],
   topic: {
     title: 'A Topic Mock Title',

client/cypress/integration/frontend/snapshots.spec.js

@@ -19,6 +19,7 @@ describe('Snapshot', () => {
           success: true,
         },
       },
+      UpdateLastModule: {},
       ModuleSnapshotsQuery: {
         module: {
           ...module,

client/src/pages/studentSubmission.vue

@@ -218,27 +218,32 @@
             const variables = {
               id: this.studentSubmission.id,
             };
-            const data = store.readQuery({query, variables});
+            const { studentSubmission } = store.readQuery({query, variables});
 
-            if (data) {
+            if (studentSubmission) {
-              if (!data.studentSubmission.submissionFeedback) {
+              let text;
-                data.studentSubmission.submissionFeedback = {
-                  '__typename': 'SubmissionFeedbackNode',
-                };
-              }
-
-              data.studentSubmission.submissionFeedback = Object.assign({}, data.studentSubmission.submissionFeedback, {
-                id: updatedSubmissionFeedback.id,
-                final: updatedSubmissionFeedback.final,
-              });
 
               if (updatedSubmissionFeedback.text !== undefined) {
                 // text is only being set on create and on turning in, then we'll update the cache with it. Otherwise, we'll trust the local state, as to not overwrite the input field
-                data.studentSubmission.submissionFeedback.text = updatedSubmissionFeedback.text;
+                text = updatedSubmissionFeedback.text;
               } else {
-                data.studentSubmission.submissionFeedback.text = this.studentSubmission.submissionFeedback ? this.studentSubmission.submissionFeedback.text : '';
+                text = this.studentSubmission.submissionFeedback ? this.studentSubmission.submissionFeedback.text : '';
               }
 
+              const submissionFeedback = Object.assign({}, studentSubmission.submissionFeedback, {
+                id: updatedSubmissionFeedback.id,
+                final: updatedSubmissionFeedback.final,
+                '__typename': 'SubmissionFeedbackNode',
+                text
+              });
+
+              const data = {
+                studentSubmission: {
+                  ...studentSubmission,
+                  submissionFeedback
+                }
+              };
+
               store.writeQuery({query, variables, data});
             }
           }