WebNovelPortal/DBConnection/AppDbContext.cs

using System.Reflection;
using DBConnection.ModelBuilders;
using DBConnection.Models;
using DBConnection.Seeders;
using Microsoft.EntityFrameworkCore;

namespace DBConnection;

public class AppDbContext : DbContext
{
    public DbSet<Novel> Novels { get; set; }
    public DbSet<Chapter> Chapters { get; set; }
    public DbSet<Author> Authors { get; set; }
    public DbSet<User> Users { get; set; }
    public DbSet<Tag> Tags { get; set; }
    public DbSet<UserNovel> UserNovels { get; set; }

    private readonly IEnumerable<ISeeder> _seeders = 
        from t in Assembly.GetExecutingAssembly().GetTypes()
        where t.IsClass && (t.Namespace?.Contains(nameof(DBConnection.Seeders)) ?? false) && typeof(ISeeder).IsAssignableFrom(t)
        select (ISeeder) Activator.CreateInstance(t);

    private static readonly IEnumerable<IModelBuilder> ModelBuilders =
        from t in Assembly.GetExecutingAssembly().GetTypes()
        where t.IsClass && (t.Namespace?.Contains(nameof(DBConnection.ModelBuilders)) ?? false) && typeof(IModelBuilder).IsAssignableFrom(t)
        select (IModelBuilder) Activator.CreateInstance(t);

    public AppDbContext(DbContextOptions options) : base(options)
    {
    }

    public override Task<int> SaveChangesAsync(CancellationToken cancellationToken = new CancellationToken())
    {
        UpdateAuditInfo();
        return base.SaveChangesAsync(cancellationToken);
    }

    private void UpdateAuditInfo()
    {
        var entries = ChangeTracker.Entries().Where(x =>
            x.Entity is BaseEntity && (x.State == EntityState.Added || x.State == EntityState.Modified));
        foreach(var entry in entries) {
            if (entry.State == EntityState.Added)
            {
                ((BaseEntity)entry.Entity).DateCreated = DateTime.Now;
            }
            ((BaseEntity)entry.Entity).DateModified = DateTime.Now;
        }
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        foreach (var builder in ModelBuilders)
        {
            builder.BuildModel(modelBuilder);
        }
        foreach (var seeder in _seeders)
        {
            seeder.SeedData(modelBuilder);
        }
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        base.OnConfiguring(optionsBuilder);
    }
}