text: const mongoose=require("mongoose");
  const {ObjectId} = require("mongodb");
  
  const userSchema = new mongoose.Schema({
      username:{type: 'string',unique: true, required: true},
      mail:{type: 'string',unique: true, required: true},
      password:{type: 'string', required: true},
      friends: [{ type : ObjectId, ref: 'user' }],
      invitations: [{ type : ObjectId, ref: 'user' }],
      number:{type: 'string'},
      avatar:{type: 'string'},
  });
  
  module.exports =mongoose.model('user',userSchema)