mongoose: Populate type with TypeScript not working

Do you want to request a feature or report a bug? bug

What is the current behavior? property in interface with type PopulatedDoc<interface & Document> has type any If the current behavior is a bug, please provide the steps to reproduce.

import mongoose, { Schema, model, Document, PopulatedDoc } from 'mongoose';
async function run() {
    mongoose.connect('mongodb://localhost:27017/test');
    // `child` is either an ObjectId or a populated document
    interface Parent {
        child?: PopulatedDoc<Child & Document>,
        name?: string
    }
    const ParentModel = model<Parent>('Parent', new Schema<Parent>({
        child: { type: 'ObjectId', ref: 'Child' },
        name: String
    }));

    interface Child {
        name?: string;
    }
    const childSchema: Schema = new Schema<Child>({ name: String });
    const ChildModel = model<Child>('Child', childSchema);

    const parent = await ParentModel.findOne({}).populate('child')
    parent!.child.name;
}

{
  "compilerOptions": {
    "target": "ES6",                      
    "module": "commonjs",                     
    "strict": true,                          
    "esModuleInterop": true,                 
    "forceConsistentCasingInFileNames": true 
  }
}

What is the expected behavior? it should support the type of given interface What are the versions of Node.js, Mongoose and MongoDB you are using? Note that “latest” is not a version. Node.js: 14.17.4 , Mongoose: 6.0.7 , MongoDB: 4.4.3

About this issue

Original URL
State: closed
Created 3 years ago
Reactions: 4
Comments: 18 (6 by maintainers)

Most upvoted comments

@vkarpov15 I’m running in the same issue as @judgegodwins regarding the populate method returning an intersection type:

ParentModel.findOne({})
  .populate<{ child: Child }>('child')
  .orFail()
  .then((doc) => {
    const t: string = doc.child.name
  })

The type of doc.child in the callback is Types.ObjectId & Child, while we expect Child | null. (iirc the null type should be automatically added since Mongoose might return it if the document was not found).

Even when using .populate<{ child: Child | null }>('child'), doc.child stays Types.ObjectId & Child.

Typescript 4.2.4 / Mongoose 6.0.13

sheerlox on Dec 19, 2021

@thiagokisaki using your example above, there’s still no name property on child.

ahmedelshenawy25 on Sep 21, 2021

@dantenol please open a new issue and follow the issue template

vkarpov15 on Feb 6, 2022

Hi, this isn’t about any compilation issues, it’s just the actual behavior of the populate regarding types doesn’t seem to be expected behavior:

The type of doc.child in the callback is Types.ObjectId & Child, while we expect Child | null. (iirc the null type should be automatically added since Mongoose might return it if the document was not found).

Even when using .populate<{ child: Child | null }>('child'), doc.child stays Types.ObjectId & Child.

Am I misunderstanding how this should work or is there something not making sense to you as well ?

sheerlox on Dec 19, 2021

@thiagokisaki we made some improvements to make this easier by passing a generic param to populate() as shown below.

import { Schema, model, Document, Types } from 'mongoose';

// `Parent` represents the object as it is stored in MongoDB
interface Parent {
  child?: Types.ObjectId,
  name?: string
}
interface Child {
  name: string;
}
// `PopulatedParent` represents the possible populated paths
interface PopulatedParent {
  child: Child | null;
}
const ParentModel = model<Parent>('Parent', new Schema({
  child: { type: 'ObjectId', ref: 'Child' },
  name: String
}));
const childSchema: Schema = new Schema({ name: String });
const ChildModel = model<Child>('Child', childSchema);

// Populate with `Paths` generic `{ child: Child }` to override `child` path
ParentModel.findOne({}).populate<Pick<PopulatedParent, 'child'>>('child').orFail().then(doc => {
  // Works
  const t: string = doc.child.name;
});

vkarpov15 on Oct 12, 2021