Overview

This lesson covers the essential controller implementations for all the remaining features of our YouTube-like backend. Each controller follows the same pattern: validate inputs → check authorization → perform DB operation → return ApiResponse.

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Comment Controllers

addComment:

const addComment = asyncHandler(async (req, res) => {
  const { videoId } = req.params;
  const { content } = req.body;
  if (!content?.trim()) throw new ApiError(400, 'Comment content is required');
  if (!mongoose.isValidObjectId(videoId)) throw new ApiError(400, 'Invalid video ID');

  const video = await Video.findById(videoId);
  if (!video) throw new ApiError(404, 'Video not found');

  const comment = await Comment.create({ content: content.trim(), video: videoId, owner: req.user._id });
  return res.status(201).json(new ApiResponse(201, comment, 'Comment added'));
});

updateComment and deleteComment — always check ownership before allowing update/delete:

const deleteComment = asyncHandler(async (req, res) => {
  const comment = await Comment.findById(req.params.commentId);
  if (!comment) throw new ApiError(404, 'Comment not found');
  if (comment.owner.toString() !== req.user._id.toString()) {
    throw new ApiError(403, 'Unauthorized to delete this comment');
  }
  await Comment.findByIdAndDelete(req.params.commentId);
  // Also delete all likes on this comment
  await Like.deleteMany({ comment: req.params.commentId });
  return res.status(200).json(new ApiResponse(200, {}, 'Comment deleted'));
});

getVideoComments with pagination and like info:

const getVideoComments = asyncHandler(async (req, res) => {
  const { videoId } = req.params;
  const { page = 1, limit = 10 } = req.query;
  const skip = (Number(page) - 1) * Number(limit);

  const comments = await Comment.aggregate([
    { $match: { video: new mongoose.Types.ObjectId(videoId) } },
    { $sort: { createdAt: -1 } },
    { $skip: skip },
    { $limit: Number(limit) },
    {
      $lookup: { from: 'users', localField: 'owner', foreignField: '_id', as: 'owner',
        pipeline: [{ $project: { fullName: 1, username: 1, avatar: 1 } }],
      },
    },
    {
      $lookup: { from: 'likes', localField: '_id', foreignField: 'comment', as: 'likes' },
    },
    {
      $addFields: {
        owner: { $first: '$owner' },
        likesCount: { $size: '$likes' },
        isLiked: { $in: [new mongoose.Types.ObjectId(req.user._id), '$likes.likedBy'] },
      },
    },
    { $project: { content: 1, owner: 1, likesCount: 1, isLiked: 1, createdAt: 1 } },
  ]);

  const total = await Comment.countDocuments({ video: videoId });
  return res.status(200).json(new ApiResponse(200, { comments, total, page, limit }, 'Comments fetched'));
});

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Like Controllers

toggleVideoLike:

const toggleVideoLike = asyncHandler(async (req, res) => {
  const { videoId } = req.params;
  const existing = await Like.findOne({ likedBy: req.user._id, video: videoId });
  if (existing) {
    await Like.findByIdAndDelete(existing._id);
    return res.status(200).json(new ApiResponse(200, { isLiked: false }, 'Like removed'));
  }
  await Like.create({ likedBy: req.user._id, video: videoId });
  return res.status(200).json(new ApiResponse(200, { isLiked: true }, 'Video liked'));
});

getLikedVideos:

const getLikedVideos = asyncHandler(async (req, res) => {
  const likes = await Like.find({ likedBy: req.user._id, video: { $exists: true } })
    .populate({ path: 'video', select: 'title thumbnail duration views owner', populate: { path: 'owner', select: 'username avatar' } })
    .sort({ createdAt: -1 });
  const videos = likes.map((l) => l.video).filter(Boolean);
  return res.status(200).json(new ApiResponse(200, videos, 'Liked videos fetched'));
});

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Playlist Controllers

const addVideoToPlaylist = asyncHandler(async (req, res) => {
  const { playlistId, videoId } = req.params;
  const playlist = await Playlist.findById(playlistId);
  if (!playlist) throw new ApiError(404, 'Playlist not found');
  if (playlist.owner.toString() !== req.user._id.toString())
    throw new ApiError(403, 'Unauthorized');

  const video = await Video.findById(videoId);
  if (!video) throw new ApiError(404, 'Video not found');

  const updated = await Playlist.findByIdAndUpdate(
    playlistId,
    { $addToSet: { videos: videoId } },  // $addToSet prevents duplicates
    { new: true }
  );
  return res.status(200).json(new ApiResponse(200, updated, 'Video added to playlist'));
});

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Video Controllers — Pagination Pattern

getAllVideos with search, sort, and pagination:

const getAllVideos = asyncHandler(async (req, res) => {
  const { page = 1, limit = 10, query = '', sortBy = 'createdAt', sortType = 'desc', userId } = req.query;
  const skip = (Number(page) - 1) * Number(limit);

  const matchStage = { isPublished: true };
  if (query) matchStage['$text'] = { $search: query };
  if (userId && mongoose.isValidObjectId(userId)) matchStage['owner'] = new mongoose.Types.ObjectId(userId);

  const videos = await Video.aggregate([
    { $match: matchStage },
    { $lookup: { from: 'users', localField: 'owner', foreignField: '_id', as: 'owner',
        pipeline: [{ $project: { fullName: 1, username: 1, avatar: 1 } }] } },
    { $addFields: { owner: { $first: '$owner' } } },
    { $sort: { [sortBy]: sortType === 'asc' ? 1 : -1 } },
    { $skip: skip },
    { $limit: Number(limit) },
    { $project: { title: 1, thumbnail: 1, duration: 1, views: 1, owner: 1, createdAt: 1 } },
  ]);

  const total = await Video.countDocuments(matchStage);
  return res.status(200).json(new ApiResponse(200, { videos, total, page, limit }, 'Videos fetched'));
});

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Key Controller Patterns Summary