Homework 3.1 MongoDB for .Net Development

MongoDB Homework 3.1 for the .Net Development is given below step by step.

Step1 :Download student.json from Download handout which is in homework url.

Use the below command to drop and import new data of student in MongoDB by using mongoimport command.

mongoimport --drop -d school -c students students.json

There should be two hundred record in the student collection. First check the data which is correctly imported or not.
see below command which help to find data in MongoDB collections

use school
db.students.count()

Correct output of count will be two hundred.

Now we need to find the student with highest average in the class . Use below query to get answer.

db.students.aggregate( [
  { '$unwind': '$scores' },
  {
    '$group':
    {
      '_id': '$_id',
      'average': { $avg: '$scores.score' }
    }
  },
  { '$sort': { 'average' : -1 } },
  { '$limit': 1 } ] )

You will get the out from the above query is : 13  .

So that the final answer of this homework is 13.

Now let's discuss to get same result through .net application.

I am going to write c# program code to complete the above process. see below code which help you to get knowledge to write code in C# in your project.

Make sure you have added mongo driver in your project otherwise it will not work.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Driver;

namespace Playground
{
  class Program
  {
    static void Main(string[] args)
    {
      MainAsync(args).Wait();
      Console.ReadKey();
    }

    static async Task MainAsync(string[] args)
    {
      var client = new MongoClient();
      var db = client.GetDatabase("m101");
      var collection = db.GetCollection<Student>("hw31");

      await collection.Find(new BsonDocument())
        .ForEachAsync(async student =>
        {
          var lowestHomeworkGrade = student.Grades
            .Where(x => x.Type == GradeType.homework)
            .OrderBy(x => x.Score)
            .First();

         
          await collection.UpdateOneAsync(
            filter: x => x.Id == student.Id,
            update: Builders<Student>.Update.PullFilter(
              field: x => x.Grades,
              filter: score => score.Score == lowestHomeworkGrade.Score && score.Type == GradeType.homework));

        
        });

      var result = await collection.Aggregate()
        .Unwind(x => x.Grades)
        .Group(new BsonDocument
        {
          { "_id", "$_id" },
          { "average", new BsonDocument("$avg", "$scores.score") }
        })
        .Sort(new BsonDocument("average", -1))
        .FirstAsync();

      Console.WriteLine(result);
    }

    private class Student
    {
      public int Id { get; set; }

      [BsonElement("name")]
      public string Name { get; set; }

      [BsonElement("scores")]
      public List<Grade> Grades { get; set; }
    }

    private class Grade
    {
      [BsonElement("type")]
      [BsonRepresentation(BsonType.String)]
      public GradeType Type { get; set; }

      [BsonElement("score")]
      public double Score { get; set; }
    }

    public enum GradeType
    {
     
      homework,
      exam,
      quiz
    }
  }
}