.populate() clobbers the return type with { [x: string]: NativeDate; }

[smbogan]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.5.3

Node.js version

22.5.1

MongoDB server version

5.0

Typescript version (if applicable)

4.9.5

Description

The Typescript type for populate's return value:

const result = await SomeModel.findOne().populate<{ otherInfo: string }>("other");

includes MergeType<{ [x: string]: NativeDate; } & ....

This causes later code to assume every property is of type NativeDate.

This was observed after upgrading from mongoose 6.12.0 to 8.5.3.

Steps to Reproduce

1. Create any model.
2. Call findOne, followed by populate with a type parameter.

Expected Behavior

The types to be properly merged without { [x: string]: NativeDate; } being included.

[ark23BLR]

@smbogan Does SomeModel in your example is constructed with timestamps schema options? Can you provide how your schema was defined?

[smbogan]

@smbogan Does SomeModel in your example is constructed with timestamps schema options?

Yes.

{
    timestamps: {
      createdAt: "createdAt",
      updatedAt: "updatedAt",
    },
}

[ark23BLR]

@smbogan You can try the following

{
    timestamps: {
      createdAt: "createdAt",
      updatedAt: "updatedAt",
    },
} as const

Alternatively, you can provide it like this:

{
    timestamps: {
      createdAt: true,
      updatedAt: true,
    },
}

Other than that

{
    timestamps: true,
}

The reason of the issue is that you provide createdAt, updatedAt values like string in typescript type, not as a literal and based on the values schema type is built. With using as const you provide the values as literal and mongoose can build a correct type.

Does it help?

[smbogan]

Using as const did fix the types. Thank you!

[ark23CIS]

@vkarpov15 Created an MR to not confuse users in case if they provide timestamp options like in case that was mentioned above