Program.cs

using MongoDB.Entities;
using MongoDB.Entities.Core;
using System.Collections.Generic;
using System.Linq;

namespace TestApp
{
    public class Zone : Entity
    {
        public int SqlId { get; set; }
    }

    public class Search : Entity
    {
        public Many<Zone> Zones { get; set; }

        public Search() => this.InitOneToMany(() => Zones);
    }

    public class _001_seed_zone_data : IMigration
    {
        public void Upgrade()
        {
            var zones = new List<Zone>();

            for (int i = 1; i <= 20; i++)
            {
                zones.Add(new Zone { SqlId = i });
            }

            zones.Save();
        }
    }

    public static class Program
    {
        private static void Main()
        {
            new DB("test", "127.0.0.1");

            DB.Migrate();

            var wantedZones = new[] { 1, 2, 3 };

            var foundZones = DB.Find<Zone>()
                                .Many(z => wantedZones.Contains(z.SqlId));

            var seach1Zones = foundZones.Where(z => new[] { 1, 2 }.Contains(z.SqlId));
            var search2Zones = foundZones.Where(z => new[] { 1, 2, 3 }.Contains(z.SqlId));

            var search1 = new Search();
            var search2 = new Search();

            DB.Save(new[] { search1, search2 });

            search1.Zones.Add(seach1Zones);
            search2.Zones.Add(search2Zones);
        }
    }
}