Beginners' guide to using MongoDB 4.0.2 and the official C# driver

namespace TestMongo
{
    using System;
    using System.Collections.Generic;
    using System.Linq;

    using MongoDB.Bson;
    using MongoDB.Bson.Serialization;
    using MongoDB.Driver;

    public partial class Program
    {
        #region Public Methods and Operators

        public static void DemoAggregation(MongoCollection<ClubMember> collection)
        {
            var sortFamiliesOperation = new BsonDocument { { "$sort", new BsonDocument { { "FamilyName", 1 } } } };
            var groupFamiliesOperation = new BsonDocument
            {
                {
                    //Sort the documents into groups
                    "$group",
                    new BsonDocument
                    {
                        //Make the unique identifier for the group a BSON element consisting
                        // of a field named FamilyId.
                        // Set its value to that of the Lastname field 
                                
                        {
                            "_id",
                            new BsonDocument { { "FamilyId", "$Lastname" } }
                            },
                        {
                            //Declare another output field and name it Count. 
                            //Increase Count's value by one for each document in the group 
                            "Count", new BsonDocument { { "$sum", 1 } }
                            },
                        {
                            //Declare an other output field and name it TotalAge. 
                            //Increase TotalAge's value by the Age value for each document in the group 
                            "TotalAge",
                            new BsonDocument { { "$sum", "$Age" } }
                            },
                        {
                            "MinAge", new BsonDocument { { "$min", "$Age" } }
                            },
                        {
                            "MaxAge", new BsonDocument { { "$max", "$Age" } }
                            }
                    }
                    }
            };

            // Example of a document formed as a result of the group operation
            //{ "_id" : { "Lastname" : "Thomas" }, "Count" : 6, "TotalAge" : 204, "MinAge" : 20, "MaxAge" : 48 }

            var projectFamilyOperation = new BsonDocument
            {
                {
                    "$project", new BsonDocument
                    {
                        //Drop the _id field, the '0' means drop
                        { "_id", 0 },
                        //Declare a new field. Set its value to the FamilyId value of the _id
                        { "FamilyName", "$_id.FamilyId" },
                        //Keep the fields detailed below. The '1' means keep
                        { "Count", 1 },
                        { "TotalAge", 1 },
                        { "MinAge", 1 },
                        { "MaxAge", 1 }
                    }
                    }
            };

            AggregateResult familyAggregate = collection.Aggregate(
                groupFamiliesOperation, projectFamilyOperation, sortFamiliesOperation);

            IEnumerable<FamilyStat> familyStats =
                familyAggregate.ResultDocuments.Select(BsonSerializer.Deserialize<FamilyStat>);

            Console.WriteLine(
                String.Format("{0,-12}{1,10}{2,12}{3,13}{4,12}", "Family", "Members", "Oldest", "Youngest", "TotalAge"));
            foreach (FamilyStat stats in familyStats)
            {
                Console.WriteLine(
                    String.Format(
                        "{0,-11}{1,8}{2,12}{3,14}{4,14}",
                        stats.FamilyName,
                        stats.Count,
                        stats.MaxAge,
                        stats.MinAge,
                        stats.TotalAge));
            }

            DateTime utcTime5yearsago = DateTime.Now.AddYears(-5).ToUniversalTime();

            var matchMembershipDateOperation = new BsonDocument
            {
                { "$match", new BsonDocument { { "MembershipDate", new BsonDocument { { "$gte", utcTime5yearsago } } } } }
            };
            var unwindCarsOperation = new BsonDocument { { "$unwind", "$Cars" } };
            var groupByCarTypeOperation = new BsonDocument
            {
                {
                    //Sort the documents into groups
                    "$group",
                    new BsonDocument
                    {
                        //Make the unique identifier for the group a BSON element consisting
                        // of a field named Car.
                        // Set its value to that of the Cars field 
                        // The Cars field is nolonger an array because it has been unwound
                        { "_id", new BsonDocument { { "Car", "$Cars" } } },
                        {
                            "Owners",
                            new BsonDocument
                            {
                                {
                                    //add a value to the Owners Array if it does not
                                    //already contain an  identical value
                                    "$addToSet",
                                    //The value to add is a BsonDocument with an identical structure to
                                    // a serialized ClubMember class.
                                    new BsonDocument
                                    {
                                        { "_id", "$_id" },
                                        { "Lastname", "$Lastname" },
                                        { "Forename", "$Forename" },
                                        { "Age", "$Age" },
                                        {
                                            "MembershipDate", "$MembershipDate"
                                            }
                                    }
                                    }
                            }
                            }
                    }
                    }
            };
            var projectMakeOfCarOperation = new BsonDocument
            { { "$project", new BsonDocument { { "_id", 0 }, { "MakeOfCar", "$_id.Car" }, { "Owners", 1 } } } };

            var sortCarsOperation = new BsonDocument { { "$sort", new BsonDocument { { "MakeOfCar", 1 } } } };
            AggregateResult aggResult = collection.Aggregate(
                matchMembershipDateOperation,
                unwindCarsOperation,
                groupByCarTypeOperation,
                projectMakeOfCarOperation,
                sortCarsOperation);
            IEnumerable<CarStat> carStats = aggResult.ResultDocuments.Select(BsonSerializer.Deserialize<CarStat>);
            foreach (CarStat stat in carStats)
            {
                Console.WriteLine("\n\rCar Marque : {0}\n\r", stat.MakeOfCar);
                IEnumerable<ClubMember> clubMembers =
                    stat.Owners.AsEnumerable().Select(BsonSerializer.Deserialize<ClubMember>).OrderBy(p => p.Lastname).
                        ThenBy(p => p.Forename).ThenBy(p => p.Age).Select(p => p);

                foreach (ClubMember member in clubMembers)
                {
                    member.PrintDetailsToScreen();
                }
            }
        }

        #endregion
    }
}