"TypeError: Cannot read property 'forEach' of undefined" when embedded object field is a reference about graffiti-mongoose

[yoadsn]

I suspect this might be a bug in Graphql.js itself. since in the "type" docs of Graphql the "args" property of a field is optional. From here:

type GraphQLFieldConfig = {
  type: GraphQLOutputType;
  args?: GraphQLFieldConfigArgumentMap;
  resolve?: GraphQLFieldResolveFn;
  deprecationReason?: string;
  description?: ?string;
}

Should I open a bug in graphql?

[tothandras]

@yoadsn looking at it

[tothandras]

feel free to open the PR, I will try to fix the tests

[yoadsn]

After many hours of debugging- I think I have found the problem - deep inside the type.js source code.
I will update later when I have a suggestion for a fix.

[tothandras]

@yoadsn Thank you, I really appreciate!

[yoadsn]

Ok, For future reference here is a brief of the problem and how it was resolved.

Since ever, graphql was memoizing access to the getFields() method of a GraphQLObjectType so that the calculation is stored internally on the _fields property and returned from that field if already calculated.

 getFields(): GraphQLFieldDefinitionMap {
    return this._fields || (this._fields =
      defineFieldMap(this, this._typeConfig.fields)
    );
  }

code here;

Now, graffiti-mongoose generates fields with reference and attaches the correct types to those fields in a big method getTypes() in type.js.
During that process in order to get the fields of a parent field of a reference field it uses the graphql getFields() method unlike how it does it for other types of fields (such as an array of reference fields).

parent = parent[segment].type.getFields();

code here

The parent variable is the internal _fields property of the GraphQLObjectType and a few rows below it is modified (partially overridden) by the correct reference type field prepared beforehand. That pre-made field does not have an empty args property and it overrides the correct value in _fields generated by graphql which did contain the args property.

Later on, when the schema and inside it that specific GraphQLObjectType object is used by graphql it checks for the existence of the args field. (which is a mistake since the spec does not require it - see above).
But since graphql assumed internal properties like _fields are under the library control - it is a reasonable invariant to assert.

The fix was to enumerate the fields using an external method which does not call the internal memoizing leaving the object "clean".

parent = getTypeFields(parent[segment].type);

This is how other fields were populated in other parts of that method.
This bug was most likely caused by this commit