ticket_manager/Data/AppDbContext.cs

using Microsoft.EntityFrameworkCore;
using TicketManager.Models;

namespace TicketManager.Data
{
    public class AppDbContext : DbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
        { }

        public DbSet<Project> Projects { get; set; }
        public DbSet<User> Users { get; set; }
        public DbSet<Ticket> Tickets { get; set; }
        public DbSet<Assignment> Assignments { get; set; }
        public DbSet<History> Edits { get; set; }
        public DbSet<Note> Notes { get; set; }
        public DbSet<File> Files { get; set; }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);
            builder.Entity<Assignment>().HasKey(a => new { a.ProjectId, a.UserId });
            builder.Entity<Assignment>().HasOne(a => a.Project).WithMany(p => p.Assignments).HasForeignKey(a => a.ProjectId);
            builder.Entity<Assignment>().HasOne(a => a.User).WithMany(u => u.Assignments).HasForeignKey(a => a.UserId);
        }
    }
}