def skiplimit(page_size, page_num): """returns a set of documents belonging to page number `page_num` where size of each page is `page_size`. """ # Calculate number of documents to skip skips = page_size * (page_num - 1) # Skip and limit cursor = db['students'].find().skip(skips).limit(page_size) # Return documents return [x for x in cursor]

 let { allPostsPage = 1, followingPostsPage = 1, limit = 25, userId, fetchOthersPosts, } = req.query; const blockedUsers = await BlockUsers.aggregate([ { $match: { $or: [ { userId: mongoose.Types.ObjectId(userId) }, { blockedUserId: mongoose.Types.ObjectId(userId) }, ], }, }, ]); allPostsPage = parseInt(allPostsPage); followingPostsPage = parseInt(followingPostsPage); const blockedUserIds = []; blockedUsers.map((user) => { if (user.userId.toString() === userId.toString()) { blockedUserIds.push(user.blockedUserId); } else if (user.blockedUserId.toString() === userId.toString()) { blockedUserIds.push(user.userId); } }); let noMoreFollowingPosts = false; let posts = []; let fakeTotalPagesFlag = false; let initialPosts = []; const followingList = await Followers.aggregate([ { $match: { following: mongoose.Types.ObjectId(userId) } }, { $project: { userId: 1, _id: 0, requestAccepted: 1 } }, ]); const followingListIds = [] followingList.map((e) => { if (e.requestAccepted === true || !e.hasOwnProperty("requestAccepted")) { followingListIds.push(mongoose.Types.ObjectId(e.userId)); } }); let noFollowers = false; if (followingListIds.length < 1) { fetchOthersPosts = "true"; noFollowers = true; } // let queryFilter=; if (fetchOthersPosts === "false") { posts = await Post.aggregate([ { $lookup: { from: "users", let: { userId: "$userId" }, pipeline: [ { $match: { $expr: { $eq: ["$_id", "$$userId"] }, }, }, { $project: { fullName: 1, userName: 1, email: 1, image: 1, privateAccount: 1 } }, ], as: "users", }, }, { $addFields: { userId: { $arrayElemAt: ["$users", 0], }, dayssince: { $trunc: { $divide: [ { $subtract: [new Date(), "$createdAt"] }, 1000 * 60 * 60 * 24, ], }, }, }, }, { $match: { $or: [ { "userId._id": { $in: followingListIds } }, { $and: [ { "userId._id": mongoose.Types.ObjectId(userId) }, { dayssince: { $lt: 2 } }, ], }, ], }, }, { $lookup: { from: "ingredients", localField: "ingredients.id", foreignField: "_id", as: "output" } }, { $addFields: { "ingredients.name": "$output.name" } }, { $project: { output: 0, postLikes: 0, userLiked: 0, ingredient: 0, dayssince: 0, users: 0, comments: 0, image: 0, video: 0 } }, { $sort: { createdAt: -1 } }, { $facet: { stage1: [{ $group: { _id: null, count: { $sum: 1 } } }], stage2: [ { $skip: (followingPostsPage - 1) * limit, }, { $limit: limit * 1 }, ], }, }, { $unwind: { path: "$stage1", }, }, { $project: { count: "$stage1.count", data: "$stage2", }, }, ]); let filteredPostsCount = posts[0] ? posts[0].data.length : 0; let count = posts[0] ? posts[0].count : 0;