Can't fetch nested mongoose queries using populate in graphQL

Question

I'm wiring up a graphQL backend with mongoose and I am having trouble with some of the conventions of mongoose for a nested query. If I have the following field in the root query:

course: {
  type: CourseType,
  args: { id: { type: new GraphQLNonNull(GraphQLID) } },
  resolve(parentValue, { id }) {
    return Course.findById(id);
  },
},

A Course Type of this:

const CourseType = new GraphQLObjectType({
  name: 'CourseType',
  fields: () => ({
    id: { type: GraphQLID },
    sections: {
      type: new GraphQLList(SectionType),
      resolve(parentValue) {
        return Course.findSections(parentValue._id);
      }
    }
  }),
});

And my model looks like this:

const CourseSchema = new Schema({
  _id: { type: String },
  sections: [{
    type: Schema.Types.String,
    ref: 'Section'
  }],
});

CourseSchema.statics.findSections = function(id) {
  return this.findById(id)
    .populate('Sections')
    .then(course => {
      return course.sections
    });
}

mongoose.model('Course', CourseSchema, 'Courses');

const SectionSchema = new Schema({
  _id: { type: String },
  course: {
    type: Schema.Types.String,
    ref: 'Course',
  },
});

mongoose.model('Section', SectionSchema, 'Sections');

I would expect that I could run a query like this:

query {
 course(id: "4Zpm8zrZYqdbr2i4t") {
  id
  sections {
    id
  }
 }
}

And I should get back a given course with all of its sections. The sections come back as an empty array while the course comes back as expected. I can tell that if I look in the findSections method that it has the proper id, but populate doesn't seem to fetch the sections.

I have a feeling that I'm running into some issue with how mongoose uses its conventions for how to name stuff but I can't for the life of me figure out what is going on. Here is what my mongoDB looks like:

MongoDB:
Courses: { _id: "4Zpm8zrZYqdbr2i4t" }
Sections: { _id: "00000000000000000", courseId: "4Zpm8zrZYqdbr2i4t" }

Locco0_0 · Accepted Answer · 2017-05-24 08:46:02Z

1

One thing that does not look correct. You want to populate for the path sections but the string is in capital letter. See the docu.

So it should look like this:

CourseSchema.statics.findSections = function(id) {
  return this.findById(id)
    .populate('sections') // lower case
    .then(course => {
      return course.sections
    });
}

answered May 24, 2017 at 8:46

Locco0_0

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5 Comments

Coherent Over a year ago

Thanks that did it! I didn't realize that my courses needs an array of all the sections AND it isn't enough to have all my sections have a courseId.

Coherent Over a year ago

Just as a final question to really make sure I understand it- would it be possibly to have a query for Section.findById in your code block above so that we can search a child collection for ids that match the parent we are querying for?

Locco0_0 Over a year ago

Im not perfectly sure what you mean. But maybe you mean the in functionality of the mongoDB.

Coherent Over a year ago

Sorry I'll try once more: 1 course has many sections. Each section has a courseId. Can I find out the sections a course has without saving the sections:[sectionId1, sectionId2...] in course? Instead I would search the sections collection for all { courseId=course._id } so go the other way?

Locco0_0 Over a year ago

Sure just use find. E.G. SectionModel.find({"course_id": <given course id>}, (error, sections) => { // do something}). But i suggest you let it like this because i think it is one of the big advantages of mongoDB and what if you want to add a section to different courses?

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