fix: If field _id present in OutputType then make it NonNull

This fix makes work with Flowtype and Relay Modern more comfortable. It
makes _id field NonNull, so no need an additional checks on the client
side is _id null or not.

Mongoose and mongo almost always have _id for the document and it is not
null. In rare cases if you tune mongoose model to have _id optional, you
should manually change type for this generated field.

Author: nodkz

package.json

@@ -78,7 +78,7 @@
     "watch": "jest --watch",
     "coverage": "jest --coverage --maxWorkers 2",
     "lint": "eslint --ext .js ./src",
-    "flow": "./node_modules/.bin/flow stop && ./node_modules/.bin/flow",
+    "flow": "./node_modules/.bin/flow",
     "test": "npm run coverage && npm run lint && npm run flow",
     "link": "yarn build && yarn link graphql-compose && yarn link graphql-compose-connection && yarn link mongoose && yarn link",
     "unlink": "yarn unlink graphql-compose && yarn unlink graphql-compose-connection && yarn unlink mongoose && yarn add graphql-compose graphql-compose-connection mongoose --dev",

src/__tests__/composeWithMongoose-test.js

@@ -3,9 +3,11 @@
 
 import mongoose from 'mongoose';
 import { TypeComposer, InputTypeComposer } from 'graphql-compose';
+import { GraphQLNonNull } from 'graphql-compose/lib/graphql';
 import { UserModel } from '../__mocks__/userModel';
 import { composeWithMongoose } from '../composeWithMongoose';
 import typeStorage from '../typeStorage';
+import GraphQLMongoID from '../types/mongoid';
 
 beforeAll(() => UserModel.base.connect());
 afterAll(() => UserModel.base.disconnect());
@@ -41,6 +43,13 @@ describe('composeWithMongoose ->', () => {
           expect.arrayContaining(['_id', 'name', 'gender', 'age'])
         );
       });
+
+      it('should have NonNull _id field', () => {
+        const tc = composeWithMongoose(UserModel);
+        expect(tc.getFieldType('_id')).toBeInstanceOf(GraphQLNonNull);
+        // $FlowFixMe
+        expect(tc.getFieldType('_id').ofType).toBe(GraphQLMongoID);
+      });
     });
 
     describe('filterFields()', () => {

src/composeWithMongoose.js

@@ -2,6 +2,7 @@
 /* eslint-disable no-use-before-define, no-param-reassign, global-require */
 
 import { TypeComposer, InputTypeComposer } from 'graphql-compose';
+import { GraphQLNonNull } from 'graphql-compose/lib/graphql';
 import type { MongooseModel } from 'mongoose';
 import type { ConnectionSortMapOpts } from 'graphql-compose-connection';
 import { convertModelToGraphQL } from './fieldsConverter';
@@ -135,6 +136,14 @@ export function composeWithMongoose(
     createResolvers(model, typeComposer, opts.resolvers || {});
   }
 
+  if (typeComposer.hasField('_id')) {
+    const fc = typeComposer.getField('_id');
+    if (fc.type && !(fc.type instanceof GraphQLNonNull)) {
+      fc.type = new GraphQLNonNull(fc.type);
+      typeComposer.setField('_id', fc);
+    }
+  }
+
   return typeComposer;
 }