"this" type is inferred to "any" within virtuals' getter function

[mrdulin]

Didn't find any information from typescript documentation.

The this is inferred to be any instead of shop document. Currently, I have to specify the type for this explicitly. Is this the currently recommended way?

import { Schema } from 'mongoose';

interface Item {
	name?: string;
}
const itemSchema = new Schema<Item>({
	name: String,
});

interface Shop {
	items: Item[];
}

const shopSchema = new Schema<Shop>(
	{
		items: {
			type: [itemSchema],
			required: true,
		},
	},
	{
		virtuals: {
			isFull: {
				// get(): boolean {
                                //     // this is `any` type
				// 	return this.items.length > 15;
				// },
				get(this: Shop): boolean {
					return this.items.length > 15;
				},
			},
		},
	},
);

mongoose: 7.4.0
typescript: ^5.1.6

[vkarpov15]

This is because you're turning off Mongoose's automatic type inference by passing the document interface as a generic to new Schema(). The following compiles fine:

import { Schema } from 'mongoose';

/*interface Item {
  name?: string;
}*/
const itemSchema = new Schema({
  name: String,
});

/*interface Shop {
  items: Item[];
}*/

const shopSchema = new Schema(
  {
    items: {
      type: [itemSchema],
      required: true,
    },
  },
  {
    virtuals: {
      isFull: {
        // get(): boolean {
                                //     // this is `any` type
        //  return this.items.length > 15;
        // },
        get(): boolean {
          const length: number = this.items.length;
          return length > 15;
        },
      },
    },
  },
);

If you want to continue passing in document interface, you would also need to pass in the virtual interface:

import { Model, Schema } from 'mongoose';

interface Item {
  name?: string;
}
const itemSchema = new Schema({
  name: String,
});

interface Shop {
  items: Item[];
}
interface ShopVirtuals {
  isFull: boolean;
}

const shopSchema = new Schema<Shop, Model<Shop>, {}, {}, ShopVirtuals>(
  {
    items: {
      type: [itemSchema],
      required: true,
    },
  },
  {
    virtuals: {
      isFull: {
        get(): boolean {
          const length: number = this.items.length;
          return length > 15;
        },
      },
    },
  },
);