Update Account Details

The simplest update controller changes user profile data. We use findByIdAndUpdate with { new: true } to get the updated document back:

const updateAccountDetails = asyncHandler(async (req, res) => {
  const { fullName, email } = req.body;
  if (!fullName || !email) throw new ApiError(400, 'fullName and email are required');

  const user = await User.findByIdAndUpdate(
    req.user._id,
    { $set: { fullName, email: email.toLowerCase().trim() } },
    { new: true }   // Return the updated document
  ).select('-password -refreshToken');

  return res.status(200).json(new ApiResponse(200, user, 'Account updated'));
});

---

Change Password Controller

const changeCurrentPassword = asyncHandler(async (req, res) => {
  const { oldPassword, newPassword, confirmPassword } = req.body;

  if (newPassword !== confirmPassword) {
    throw new ApiError(400, 'New password and confirm password do not match');
  }
  if (newPassword.length < 8) throw new ApiError(400, 'Password must be at least 8 characters');

  // Fetch user WITH password (select: false means it won't be there by default)
  const user = await User.findById(req.user._id).select('+password');

  const isOldPasswordCorrect = await user.isPasswordCorrect(oldPassword);
  if (!isOldPasswordCorrect) throw new ApiError(401, 'Old password is incorrect');

  user.password = newPassword;  // Pre-save hook will hash it
  await user.save({ validateBeforeSave: false });

  return res.status(200).json(new ApiResponse(200, {}, 'Password changed successfully'));
});

---

Update Avatar (with Cloudinary cleanup)

When updating an avatar, we must:

1. Get the new file from req.file (use upload.single('avatar') middleware)
2. Upload new file to Cloudinary
3. Get the old avatar URL from the current user document
4. Extract the public_id from the old URL and delete it from Cloudinary
5. Update the user's avatar URL in the database

const updateUserAvatar = asyncHandler(async (req, res) => {
  const avatarLocalPath = req.file?.path;
  if (!avatarLocalPath) throw new ApiError(400, 'Avatar file is required');

  const newAvatar = await uploadOnCloudinary(avatarLocalPath);
  if (!newAvatar?.secure_url) throw new ApiError(500, 'Avatar upload failed');

  // Get old avatar public_id to delete from Cloudinary
  const oldUser = await User.findById(req.user._id).select('avatar');
  if (oldUser?.avatar) {
    const publicId = oldUser.avatar.split('/').pop()?.split('.')[0];
    if (publicId) await deleteFromCloudinary(publicId);
  }

  const user = await User.findByIdAndUpdate(
    req.user._id,
    { $set: { avatar: newAvatar.secure_url } },
    { new: true }
  ).select('-password -refreshToken');

  return res.status(200).json(new ApiResponse(200, user, 'Avatar updated'));
});

---

Get User Channel Profile — Aggregation Pipeline

This is one of the most advanced controllers — it uses MongoDB aggregation to get a user's channel info including subscriber count, subscription count, and whether the current user is subscribed, all in a single query:

const getUserChannelProfile = asyncHandler(async (req, res) => {
  const { username } = req.params;
  if (!username?.trim()) throw new ApiError(400, 'Username is required');

  const channel = await User.aggregate([
    // Stage 1: Find user by username
    { $match: { username: username.toLowerCase().trim() } },

    // Stage 2: Look up subscribers (documents where channel = this user)
    {
      $lookup: {
        from: 'subscriptions',
        localField: '_id',
        foreignField: 'channel',
        as: 'subscribers',
      },
    },

    // Stage 3: Look up who this user subscribes to
    {
      $lookup: {
        from: 'subscriptions',
        localField: '_id',
        foreignField: 'subscriber',
        as: 'subscribedTo',
      },
    },

    // Stage 4: Add computed fields
    {
      $addFields: {
        subscribersCount: { $size: '$subscribers' },
        channelsSubscribedToCount: { $size: '$subscribedTo' },
        isSubscribed: {
          $cond: {
            if: { $in: [req.user?._id, '$subscribers.subscriber'] },
            then: true,
            else: false,
          },
        },
      },
    },

    // Stage 5: Project only necessary fields
    {
      $project: {
        fullName: 1,
        username: 1,
        avatar: 1,
        coverImage: 1,
        email: 1,
        subscribersCount: 1,
        channelsSubscribedToCount: 1,
        isSubscribed: 1,
        createdAt: 1,
      },
    },
  ]);

  if (!channel?.length) throw new ApiError(404, 'Channel not found');

  return res.status(200).json(new ApiResponse(200, channel[0], 'Channel profile fetched'));
});

---

Get Watch History — Nested $lookup

const getWatchHistory = asyncHandler(async (req, res) => {
  const user = await User.aggregate([
    { $match: { _id: new mongoose.Types.ObjectId(req.user._id) } },
    {
      $lookup: {
        from: 'videos',
        localField: 'watchHistory',
        foreignField: '_id',
        as: 'watchHistory',
        pipeline: [
          {
            $lookup: {
              from: 'users',
              localField: 'owner',
              foreignField: '_id',
              as: 'owner',
              pipeline: [
                { $project: { fullName: 1, username: 1, avatar: 1 } },
              ],
            },
          },
          { $addFields: { owner: { $first: '$owner' } } },
        ],
      },
    },
  ]);

  return res.status(200).json(new ApiResponse(200, user[0].watchHistory, 'Watch history fetched'));
});

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Key Concepts Used in Update Controllers