fix: setting a field to null does not delete it via GraphQL API (#7649)

BREAKING CHANGE: To delete a field via the GraphQL API, the field value has to be set to `null`. Previously, setting a field value to `null` would save a null value in the database, which was not according to the [GraphQL specs](https://spec.graphql.org/June2018/#sec-Null-Value). To delete a file field use `file: null`, the previous way of using `file: { file: null }` has become obsolete.

src/GraphQL/loaders/defaultGraphQLTypes.js

@@ -357,21 +357,17 @@ const FILE_INFO = new GraphQLObjectType({
 
 const FILE_INPUT = new GraphQLInputObjectType({
   name: 'FileInput',
+  description:
+    'If this field is set to null the file will be unlinked (the file will not be deleted on cloud storage).',
   fields: {
     file: {
-      description:
-        'A File Scalar can be an url or a FileInfo object. If this field is set to null the file will be unlinked.',
+      description: 'A File Scalar can be an url or a FileInfo object.',
       type: FILE,
     },
     upload: {
       description: 'Use this field if you want to create a new file.',
       type: GraphQLUpload,
     },
-    unlink: {
-      description:
-        'Use this field if you want to unlink the file (the file will not be deleted on cloud storage)',
-      type: GraphQLBoolean,
-    },
   },
 });
 

src/GraphQL/loaders/parseClassMutations.js

@@ -10,6 +10,14 @@ import { ParseGraphQLClassConfig } from '../../Controllers/ParseGraphQLControlle
 import { transformClassNameToGraphQL } from '../transformers/className';
 import { transformTypes } from '../transformers/mutation';
 
+const filterDeletedFields = fields =>
+  Object.keys(fields).reduce((acc, key) => {
+    if (typeof fields[key] === 'object' && fields[key]?.__op === 'Delete') {
+      acc[key] = null;
+    }
+    return acc;
+  }, fields);
+
 const getOnlyRequiredFields = (
   updatedFields,
   selectedFieldsString,
@@ -131,7 +139,7 @@ const load = function (parseGraphQLSchema, parseClass, parseClassConfig: ?ParseG
             [getGraphQLQueryName]: {
               ...createdObject,
               updatedAt: createdObject.createdAt,
-              ...parseFields,
+              ...filterDeletedFields(parseFields),
               ...optimizedObject,
             },
           };
@@ -240,7 +248,7 @@ const load = function (parseGraphQLSchema, parseClass, parseClassConfig: ?ParseG
             [getGraphQLQueryName]: {
               objectId: id,
               ...updatedObject,
-              ...parseFields,
+              ...filterDeletedFields(parseFields),
               ...optimizedObject,
             },
           };