Typescript mongoose static model method "Property does not exist on type"

Question

I am currently trying to add a static method to my mongoose schema but I can't find the reason why it doesn't work this way.

My model:

import * as bcrypt from 'bcryptjs';
import { Document, Schema, Model, model } from 'mongoose';

import { IUser } from '../interfaces/IUser';

export interface IUserModel extends IUser, Document {
    comparePassword(password: string): boolean;
}

export const userSchema: Schema = new Schema({
    email: { type: String, index: { unique: true }, required: true },
    name: { type: String, index: { unique: true }, required: true },
    password: { type: String, required: true }
});

userSchema.method('comparePassword', function (password: string): boolean {
    if (bcrypt.compareSync(password, this.password)) return true;
    return false;
});

userSchema.static('hashPassword', (password: string): string => {
    return bcrypt.hashSync(password);
});

export const User: Model<IUserModel> = model<IUserModel>('User', userSchema);

export default User;

IUser:

export interface IUser {
    email: string;
    name: string;
    password: string;
}

If I now try to call User.hashPassword(password) I am getting the following error [ts] Property 'hashPassword' does not exist on type 'Model<IUserModel>'.

I know that I didn't define the method anywhere but I don't really know where I could put it as I can't just put a static method into an interface. I hope you can help my find the error, thanks in advance!

Answer 1

I was having the same problem as you, and then finally managed to resolve it after reading the documentation in the TS mongoose typings (which I didn't know about before, and I'm not sure how long the docs have been around), specifically this section.

---

As for your case, you'll want to follow a similar pattern to what you currently have, although you'll need to change a few things in both files.

IUser file

1. Rename IUser to IUserDocument. This is to separate your schema from your instance methods.
2. Import Document from mongoose.
3. Extend the interface from Document.

Model file

1. Rename all instances of IUser to IUserDocument, including the module path if you rename the file.
2. Rename only the definition of IUserModel to IUser.
3. Change what IUser extends from, from IUserDocument, Document to IUserDocument.
4. Create a new interface called IUserModel which extends from Model<IUser>.
5. Declare your static methods in IUserModel.
6. Change the User constant type from Model<IUserModel> to IUserModel, as IUserModel now extends Model<IUser>.
7. Change the type argument on your model call from <IUserModel> to <IUser, IUserModel>.

---

Here's what your model file would look like with those changes:

import * as bcrypt from 'bcryptjs';
import { Document, Schema, Model, model } from 'mongoose';

import { IUserDocument } from '../interfaces/IUserDocument';

export interface IUser extends IUserDocument {
    comparePassword(password: string): boolean; 
}

export interface IUserModel extends Model<IUser> {
    hashPassword(password: string): string;
}

export const userSchema: Schema = new Schema({
    email: { type: String, index: { unique: true }, required: true },
    name: { type: String, index: { unique: true }, required: true },
    password: { type: String, required: true }
});

userSchema.method('comparePassword', function (password: string): boolean {
    if (bcrypt.compareSync(password, this.password)) return true;
    return false;
});

userSchema.static('hashPassword', (password: string): string => {
    return bcrypt.hashSync(password);
});

export const User: IUserModel = model<IUser, IUserModel>('User', userSchema);

export default User;

And your (newly renamed) ../interfaces/IUserDocument module would look like this:

import { Document } from 'mongoose';

export interface IUserDocument extends Document {
    email: string;
    name: string;
    password: string;
}

Answer 2

I think you are having the same issue that I just struggled with. This issue is in your call. Several tutorials have you call the .comparePassword() method from the model like this.

User.comparePassword(candidate, cb...)

This doesn't work because the method is on the schema not on the model. The only way I was able to call the method was by finding this instance of the model using the standard mongoose/mongo query methods.

Here is relevant part of my passport middleware:

passport.use(
  new LocalStrategy({
    usernameField: 'email'
  },
    function (email: string, password: string, done: any) {
      User.findOne({ email: email }, function (err: Error, user: IUserModel) {
        if (err) throw err;
        if (!user) return done(null, false, { msg: 'unknown User' });
        user.schema.methods.comparePassword(password, user.password, function (error: Error, isMatch: boolean) {
          if (error) throw error;
          if (!isMatch) return done(null, false, { msg: 'Invalid password' });
          else {
            console.log('it was a match'); // lost my $HÏT when I saw it
            return done(null, user);
          }
        })
      })
    })
);

So I used findOne({}) to get the document instance and then had to access the schema methods by digging into the schema properties on the document user.schema.methods.comparePassword

A couple of differences that I have noticed:

1. Mine is an instance method while yours is a static method. I'm confident that there is a similar method access strategy.
2. I found that I had to pass the hash to the comparePassword() function. perhaps this isn't necessary on statics, but I was unable to access this.password

Answer 3

For future readers:

Remember that we are dealing with two different Mongo/Mongoose concepts: a Model, and Documents.

Many Documents can be created from a single Model. The Model is the blueprint, the Document is the thing created according to the Model's instructions.

Each Document contains its own data. Each also carries their own individual instance methods which are tied to its own this and only operate on that one specific instance.

The Model can have 'static' methods which are not tied to a specific Document instance, but operate over the whole collection of Documents.

How this all relates to TypeScript:

• Extend Document to define types for instance properties and .method functions.
• Extend the Model (of a Document) to define types for .static functions.

The other answers here have decent code, so look at them and trace through the differences between how Documents are defined and how Models are defined.

And remember when you go to use these things in your code, the Model is used to create new Documents and to call static methods like User.findOne or your custom statics (like User.hashPassword is defined above).

And Documents are what you use to access the specific data from the object, or to call instance methods like this.save and custom instance methods like this.comparePassword defined above.

Answer 4

I cannot see your IUser interface however I suspect that you have not included the methods in there. EG

export interface IUser {
    email: string,
    hash: string,
    salt: string,

    setPassword(password: string): void,
    validPassword(password: string): boolean,
    generateJwt(): string
}

typescript will then recognize your methods and stop complaining

Answer 5

So the one with 70 updates I also gave an upvote. But it is not a complete solution. He uses a trivial example based on the OP. However, more often than not when we use statics and methods in order to extend the functionality of the model, we want to reference the model itself. The problem with his solution is he using a callback function which means the value of this will not refer to the class context but rather a global.

The first step is to invoke the statics property rather than pass the property as an argument to the static function:

schema.statics.hashPassword

Now we cannot assign an arrow function to this member, for this inside the arrow function will still refer to the global object! We have to use function expression syntax in order to capture this in the context of the model:

schema.statics.hashPassword = async function(password: string): Promise<string> {
    console.log('the number of users: ', await this.count({}));
    ...
}

Answer 6

Refer : https://mongoosejs.com/docs/typescript.html

1. Just create an interface before the schema which represents a document structure.
2. Add the interface type to the model.
3. Export the model.

Quoting below from mongoose docs:

import { Schema, model, connect } from 'mongoose';

// 1. Create an interface representing a document in MongoDB.
interface User {
  name: string;
  email: string;
  avatar?: string;
}

// 2. Create a Schema corresponding to the document interface.
const schema = new Schema<User>({
  name: { type: String, required: true },
  email: { type: String, required: true },
  avatar: String
});

// 3. Create a Model.
const UserModel = model<User>('User', schema);

If you add any method to the schema, add its definition in the interface as well.