1. i have created groups , which has members , each member has a group array displaying which they are part of . if i delete a group i want that user’s group array also updates. i am using express and mongodb for my project here is my code:

2. group controller

   const Group = require("../models/Group");
   const User = require("../models/User");
   
   const createGroup = async (req, res) => {
     try {
       const { name, members } = req.body;
       const adminId = req.user.userId;
   
       // Get admin details
       const admin = await User.findById(adminId);
   
       // Process members array
       const groupMembers = await Promise.all(
         members.map(async (member) => {
           if (member.email) {
             const user = await User.findOne({ email: member.email });
             if (user) {
               return { user: user._id, name: user.name, email: user.email };
             }
           }
           return { name: member.name, email: member.email };
         })
       );
   
       // Add admin as the first member
       groupMembers.unshift({
         user: admin._id,
         name: admin.name,
         email: admin.email,
       });
   
       const group = new Group({
         name,
         admin: adminId,
         members: groupMembers,
       });
   
       await group.save();
   
   
       // **Update each member's groups array**
       for (const member of groupMembers) {
         if (member.user) {
           const user = await User.findById(member.user);
           user.groups.push(group._id);
           await user.save();
         }
       }
       res.status(201).json({ message: "Group created successfully", group });
     } catch (error) {
       console.error("Error creating group:", error);
       res.status(500).json({ error: "Failed to create group" });
     }
   };
   
   const addMember = async (req, res) => {
     try {
       const { groupId, member } = req.body;
       const userId = req.user.userId;
   
       const group = await Group.findById(groupId);
       if (!group) {
         return res.status(404).json({ error: "Group not found" });
       }
   
       if (group.admin.toString() !== userId) {
         return res
           .status(403)
           .json({ error: "Only the group admin can add members" });
       }
   
       const newMember = member.email
         ? await User.findOne({ email: member.email })
         : null;
   
       group.members.push(
         newMember
           ? { user: newMember._id, name: newMember.name, email: newMember.email }
           : { name: member.name, email: member.email }
       );
       // **Update the new member's groups array**
       await group.save();
       if (newMember) {
         newMember.groups.push(group._id);
         await newMember.save();
       }
   
       res.status(200).json({ message: "Member added successfully", group });
     } catch (error) {
       console.error("Error adding member:", error);
       res.status(500).json({ error: "Failed to add member" });
     }
   };
   
   const removeMember = async (req, res) => {
     try {
       const { groupId, memberId } = req.body;
       const userId = req.user.userId;
   
       const group = await Group.findById(groupId);
       if (!group) {
         return res.status(404).json({ error: "Group not found" });
       }
   
       if (group.admin.toString() !== userId) {
         return res
           .status(403)
           .json({ error: "Only the group admin can remove members" });
       }
   
       group.members = group.members.filter(
         (member) => member._id.toString() !== memberId
       );
       await group.save();
       // **Update the member's groups array**
       const member = await User.findById(memberId);
       if (member) {
         member.groups = member.groups.filter(
           (group) => group.toString() !== groupId
         );
         await member.save();
       }
   
       res.status(200).json({ message: "Member removed successfully", group });
     } catch (error) {
       console.error("Error removing member:", error);
       res.status(500).json({ error: "Failed to remove member" });
     }
   };
   
   const leaveGroup = async (req, res) => {
     try {
       const { groupId } = req.body;
       const userId = req.user.userId;
   
       const group = await Group.findById(groupId);
       if (!group) {
         return res.status(404).json({ error: "Group not found" });
       }
   
       // If the admin is leaving
       if (group.admin.toString() === userId) {
         // Transfer admin rights to the next member
         const nextAdmin = group.members.find(
           (member) => member.user && member.user.toString() !== userId
         );
         if (!nextAdmin) {
           return res
             .status(400)
             .json({
               error: "Cannot leave the group without transferring admin rights",
             });
         }
         group.admin = nextAdmin.user;
       }
   
       // Remove the member from the group
       group.members = group.members.filter((member) =>
         member.user ? member.user.toString() !== userId : true
       );
       await group.save();
       // **Update the user's groups array**
       const user = await User.findById(userId);
       user.groups = user.groups.filter((group) => group.toString() !== groupId);
       await user.save();
   
       res.status(200).json({ message: "Left group successfully", group });
     } catch (error) {
       console.error("Error leaving group:", error);
       res.status(500).json({ error: "Failed to leave group" });
     }
   };
   
   const editGroup = async (req, res) => {
     try {
       const { groupId, name } = req.body;
       const userId = req.user.userId;
   
       const group = await Group.findById(groupId);
       if (!group) {
         return res.status(404).json({ error: "Group not found" });
       }
   
       if (group.admin.toString() !== userId) {
         return res
           .status(403)
           .json({ error: "Only the group admin can edit group details" });
       }
   
       group.name = name;
       await group.save();
   
       res
         .status(200)
         .json({ message: "Group details updated successfully", group });
     } catch (error) {
       console.error("Error editing group:", error);
       res.status(500).json({ error: "Failed to edit group" });
     }
   };
   
   const addFriendstoGroup = async (req, res) => {
     try {
       const { groupId, friendId } = req.body;
       const userId = req.user.userId;
   
       const group = await Group.findById(groupId);
       if (!group) {
         return res.status(404).json({ error: "Group not found" });
       }
   
       if (group.admin.toString() !== userId) {
         return res
           .status(403)
           .json({ error: "Only the group admin can add members" });
       }
       const friend = await User.findById(friendId);
       if (!friend) {
         return res.status(404).json({ error: "Friend not found" });
       }
   
       const isAlreadyMember = group.members.some(
         (member) => member.user && member.user.toString() == friendId
       );
       if (isAlreadyMember) {
         res.status(404).json({ error: "Friend is already a member of group" });
       }
   
       group.members.push({
         user: friend._id,
         name: friend.name,
         email: friend.email,
       });
       await group.save();
       // **Update the friend's groups array**
       friend.groups.push(group._id);
       await friend.save();
       res
         .status(201)
         .json({ message: "Friend added to group successfully", group });
     } catch (error) {
       console.error("Error adding friend to group:", error);
       res.status(500).json({ error: "Failed to add friend to group" });
     }
   };
   
   module.exports = {
     createGroup,
     addMember,
     removeMember,
     leaveGroup,
     editGroup,
     addFriendstoGroup,
   };
   
   

3. my user model :

   const mongoose = require("mongoose");
   const bcrypt = require("bcrypt");
   
   const userSchema = new mongoose.Schema({
     name: {
       type: String,
       required: true,
     },
     email: {
       type: String,
       required: true,
       unique: true,
     },
     password: {
       type: String,
       required: true,
     },
     friends: [
       {
         type: mongoose.Schema.Types.ObjectId,
         ref: "User",
       },
     ],
     groups: [
       {
         type: mongoose.Schema.Types.ObjectId,
         ref: "Group",
       },
     ],
     createdAt: {
       type: Date,
       default: Date.now,
     },
   });
   
   userSchema.pre("save", async function (next) {
     if (this.isModified("password") || this.isNew) {
       this.password = await bcrypt.hash(this.password, 10);
     }
     next();
   });
   
   module.exports = mongoose.model("User", userSchema, "User");
   
   

i deleted a record from database and i was expecting that it would update the arrays