Demo/Data/RemoteData/RemoteDataBase/RemoteDataBaseContext.cs

using Microsoft.EntityFrameworkCore;
using Posechaemost.Data.RemoteData.RemoteDataBase.DAO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Posechaemost.Data.RemoteData.RemoteDataBase
{
    public class RemoteDataBaseContext: DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder){
            optionsBuilder.UseNpgsql("Host=localhost; Database=presencedb; Username=postgres; Password=123");
        }

        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.UserId);
            modelBuilder.Entity<UserDao>().Property(user => user.UserId).ValueGeneratedOnAdd();
            modelBuilder.Entity<PresenceDao>().HasKey(presence => new {
            presence.User,
            presence.Date,
            presence.IsAttendence,
            presence.ClassNumber
});
        }

        
        public DbSet<GroupDao> Groups{ get; set; }
        public DbSet<UserDao> Users{ get; set; }
        public DbSet<PresenceDao> Presences{ get; set; }
    }
}