I'm trying to share some base interfaces between the client code and the server code. I'm having problems when using the interfaces to create data models in mongoose.

The problem I have is how to access the document._id property in the client. I can't add _id to the User interface without causing compilation errors and I can't access _id without declaring it.

My project layout:

/src
-/client
--/user.service.ts
-/server
--/models
---/user.model.ts
-/common
--/common.d.ts

user.service.ts

import { User } from 'common'

 deleteUser(user: User): Promise<User> {
   return this.http.delete( 'http://someurl/api/users' + user._id )
     .toPromise()
     .then( resp => resp.json().data as User )
     .catch( err => this.errorHandler(err) );
 }

user.model.ts

import { model, Schema, Document } from 'mongoose';
import { User } from 'common';

let UserSchema = new Schema {
  firstName: String,
  lastName: String,
  email: String
}

export interface UserDocument extends User, Document { }

export var UserModel:Model<UserDocument> = model<UserDocument>('Users', UserSchema);

common.d.ts

declare module 'common' {
  export interface User {
    firstName: string;
    lastName: string;
    email: string;
  }
}

Thanks for the help