Mongoose typescript model 创建多个连接

Question

I'm trying to create a model while using multiple connections ( following the docs ) but I get the following error:

TS2345: Argument of type 'Schema<Document<any>, Model<Document<any>>>' is not assignable to parameter of
type 'Schema<UserInterface, UserModelInterface>'.
Types of property 'methods' are incompatible.
... (a bunch of 'is not assignable - is missing the following properties' errors follow) ...

My code looks like this:

_database.ts

import mongoose from "mongoose";

// const mongo = mongoose.connection(process.env.DB_URI!, {
const mongo = mongoose.createConnection(process.env.DB_URI!, {
    useUnifiedTopology: true,
    useNewUrlParser: true,
    useFindAndModify: false,
    useCreateIndex: true
})

export default mongo

_UserModel.ts

import mongoose, {Model} from 'mongoose';
import bcrypt from 'bcrypt'
import database from "../database";

interface UserDocumentInterface extends mongoose.Document {
    firstname: string
    lastname: string
    ...
}
    
interface UserInterface extends UserDocumentInterface {
    // Instance methods
    hashPassword(password: string): Promise<string>
    ...
}
    
export interface UserModelInterface extends Model<UserInterface> {
    // Static methods
    // Currently empty
}

const UserSchema = new mongoose.Schema({
    firstname: {
        type: String,
        required: true,
        trim: true
    },
    lastname: {
        type: String,
        required: true,
        index: true,
        trim: true,
    },
    ...
})

// Methods definitions
UserSchema.methods.hashPassword = async function(password) {
    return await bcrypt.hash(password, 10);
}
...

// const User: UserModelInterface = mongoose.model<UserInterface, UserModelInterface>('User', UserSchema)
const User = database.model<UserInterface, UserModelInterface>('User', UserSchema)
export default User

The error appears on UserSchema in const User = database.model<UserInterface, UserModelInterface>('User', UserSchema)

What I don't understand is why this line works without issues

const User: UserModelInterface = mongoose.model<UserInterface, UserModelInterface>('User', UserSchema)

but this one throws an error

const User = database.model<UserInterface, UserModelInterface>('User', UserSchema)

when the only thing that changes is the connection type, mongoose.createConnection() as opposed to mongoose default connection

Answer 1

Turns out that as of version mongoose 5.11.11 there are some conflicts with @types/mongoose that break class inheritance when using typescript ( see this issue ). I also found the solution to my problem in this discussion , it revolves around moving the Document and Model interface from the model to the schema constructor.

In practice it means turning this

const UserSchema = new mongoose.Schema({
    firstname: {
        type: String,
        required: true,
        trim: true
    },
    lastname: {
        type: String,
        required: true,
        index: true,
        trim: true,
    },
    ...
})
    
const User = database.model<UserInterface, UserModelInterface>('User', UserSchema)
export default User

into this

const UserSchema = new mongoose.Schema<UserInterface, UserModelInterface>({
    firstname: {                            // INTERFACES GO HERE 
        type: String,
        required: true,
        trim: true
    },
    lastname: {
        type: String,
        required: true,
        index: true,
        trim: true,
    },
    ...
})
                // INSTEAD OF HERE
const User = database.model('User', UserSchema)
export default User

To me this looks like a temporary fix, the issue will probably affect only v5.11.11 as it's being patched in 5.11.12 so I suggest visiting the links above to see the issue status before using this suggestion.