Demo/Data/RemoteData/RemoteDataBase/RemoteDatabaseContext.cs

using Demo.Data.RemoteData.RemoteDataBase.DAO;
using Microsoft.EntityFrameworkCore;

namespace Demo.Data.RemoteData.RemoteDataBase
{
    public class RemoteDatabaseContext: DbContext
    {
        public DbSet<GroupDAO> Groups {get; set; }
        public DbSet<UserDAO> Users {get; set;}
        public DbSet<PresenceDAO> PresenceDaos{get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseNpgsql("Host=localhost;Port=5433;Username=myuser;Password=mypassword;Database=mydatabase");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<GroupDAO>().HasKey(group => group.ID);
            modelBuilder.Entity<GroupDAO>().Property(group => group.ID).ValueGeneratedOnAdd();
            modelBuilder.Entity<UserDAO>().HasKey(user => user.Guid);
            modelBuilder.Entity<UserDAO>().Property(user => user.Guid).ValueGeneratedOnAdd();
            modelBuilder.Entity<PresenceDAO>().HasKey(presence => new {
                presence.UserGuid,
                presence.Date,
                presence.LessonNumber
            });
        }
    }
}