用打字稿和猫鼬创建用户模型

Question

我一直在学习有关使用node，typescript和mongodb的微服务的课程，而我一直困扰着这个问题几天。

我不明白，为什么接口UserModel最终需要<UserDoc>？我知道build(attrs: userAttrs): UserDoc;在这里我们指定了一个将在UserModel上使用的函数，它将返回一个UserDoc。但是我不明白这个interface UserModel extends mongoose.Model<UserDoc>

// an interface that describes properties that are required to create a new user
interface userAttrs {
  email: string;
  password: string;
}

//an interface that describes the properties that user model has. It's gonna say there's gonna be build function on user model
interface UserModel extends mongoose.Model<UserDoc> {
  build(attrs: userAttrs): UserDoc;
}

//an interface thath describes properties that user document has
interface UserDoc extends mongoose.Document {
  email: string;
  password: string;
}

const userSchema = new mongoose.Schema({
  email: {
    type: String,
    required: true,
  },
  password: {
    type: String,
    required: true,
  },
});

userSchema.statics.build = (attrs: userAttrs) => {
  return new User(attrs);
};

const User = mongoose.model<UserDoc, UserModel>('User', userSchema);

const user = User.build({
  email: 'test@gmail.com',
  password: 'password',
});

console.log(user);

export { User };