Mongoose .populate() not working correctly - node.js

Question

I'm trying to create a Tumblr clone with GraphQL and MERN. Right now I'm just trying to create the template for posts with photos.
Just in case it's relevant, I am doing regular REST post requests with axios and express for the image files. I take the response from those, map over the _ids and send them in the createPost mutation.
In graphiql I can query for a single Image model and get everything back fine, like so:
{
image(_id: "someId"){
_id
url
created
}
}
But when I do a subquery with the ObjectIds I've pushed into the Post arrays I get null for everything besides _id and __typename:
{
post(_id: "someId"){
_id
mainImages {
_id //returns value
url //returns null
created //returns null
__typename //returns value
}
}
}
The posts have two arrays of objects with ObjectId and ref for images, the Post model:
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const PostSchema = new Schema({
mainImages: [
{
type: Schema.Types.ObjectId,
ref: 'Image'
}
],
bodyImages: [
{
type: Schema.Types.ObjectId,
ref: 'Image'
}
],
})
module.exports = mongoose.model('Post', PostSchema, 'posts')
The Image model:
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const ImageSchema = new Schema({
url: {
type: String,
required: true
},
created: {
type: Date,
required: true
}
})
module.exports = Image = mongoose.model('Image', ImageSchema, 'images');
The PostType:
const PostType = new GraphQLObjectType({
name: 'PostType',
fields: () => ({
_id: { type: GraphQLID },
mainImages: {
type: new GraphQLList(ImageType),
resolve(parentValue) {
return Post.findById(parentValue._id)
.populate('images')
.then(post => post.mainImages)
}
},
bodyImages: {
type: new GraphQLList(ImageType),
resolve(parentValue) {
return Post.findById(parentValue._id)
.populate('images')
.then(post => post.bodyImages)
}
},
})
})
module.exports = PostType;
I'm wondering if .populate('images') isn't working correctly. I thought that if you have the ObjectIds then .populate() can take care of the rest. I've been looking around at a bunch of different questions but none of them have seemed to be relevant enough to my situation, and the GraphQL and Mongoose docs also haven't given me a breakthrough yet.

Answer 1

Alright so in the latest edition of I wasn't reading the docs correctly, I finally figured out what I was doing wrong.
.populate() takes a string that denotes a path to the field within the document that you're trying to populate the field of.
I figured out the solution while I was reading about populating multiple fields in a single document.
For some reason I thought the 'path' was supposed to point to the name of the collection in the database:
const PostType = new GraphQLObjectType({
name: 'PostType',
fields: () => ({
_id: { type: GraphQLID },
mainImages: {
type: new GraphQLList(ImageType),
resolve(parentValue) {
return Post.findById(parentValue._id)
.populate('images') //incorrectly pointing towards the collection in db
.then(post => post.mainImages)
}
},
bodyImages: {
type: new GraphQLList(ImageType),
resolve(parentValue) {
return Post.findById(parentValue._id)
.populate('images') //incorrectly pointing towards the collection in db
.then(post => post.bodyImages)
}
},
})
})
module.exports = PostType;
It's supposed to point back in to the document/model itself:
const PostType = new GraphQLObjectType({
name: 'PostType',
fields: () => ({
_id: { type: GraphQLID },
mainImages: { //this is the 'path'
type: new GraphQLList(ImageType),
resolve(parentValue) {
return Post.findById(parentValue._id)
.populate('mainImages') //that's referenced here
.then(post => post.mainImages)
}
},
bodyImages: {
type: new GraphQLList(ImageType),
resolve(parentValue) {
return Post.findById(parentValue._id)
.populate('bodyImages') //and once again
.then(post => post.bodyImages)
}
}
})
})
export default PostType;
And that solved my problem, all of my GraphQL subqueries are working correctly now. Another day, another episode of I didn't read the docs correctly.