The main goal of ModelBuilderExtentions.cs is to use DataAnnotations more in our tables instead of using Fluent. The other files are mere examples.

ApplicationDbContext.cs

namespace MyDotNetCore.App
{
    using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
    using Microsoft.EntityFrameworkCore;
    public class ApplicationDbContext : IdentityDbContext
    {
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
            : base(options)
        {
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.SetDefaultValuesTableName();
        }
    }
}

ModelBuilderExtensions.cs

namespace Microsoft.EntityFrameworkCore
{
    using System;
    using System.ComponentModel;
    using System.ComponentModel.DataAnnotations.Schema;
    using System.Linq;
    using System.Reflection;
    public static class ModelBuilderExtensions
    {
        public static void SetDefaultValuesTableName(this ModelBuilder modelBuilder)
        {
            foreach (var entity in modelBuilder.Model.GetEntityTypes().Where(x => x.ClrType.GetCustomAttribute(typeof(TableAttribute)) != null))
            {
                var entityClass = entity.ClrType;
                var tAttr = entityClass.GetCustomAttribute(typeof(TableAttribute)) as TableAttribute;

                modelBuilder.Entity(entityClass).ToTable(tAttr.Name);

                foreach (var property in entityClass.GetProperties().Where(p => (p.PropertyType == typeof(DateTime) || p.PropertyType == typeof(Guid)) && p.CustomAttributes.Any(a => a.AttributeType == typeof(DatabaseGeneratedAttribute) && !p.CustomAttributes.Any(c=>c.AttributeType == typeof(DefaultValueAttribute)))))
                {
                    var defaultValueSql = "GetDate()";
                    if (property.PropertyType == typeof(Guid))
                    {
                        defaultValueSql = "newsequentialid()";
                    }
                    modelBuilder.Entity(entityClass).Property(property.Name).HasDefaultValueSql(defaultValueSql);
                }

                foreach (var property in entityClass.GetProperties().Where(p => p.CustomAttributes.Any(a => a.AttributeType == typeof(DefaultValueAttribute))))
                {
                    var pAttr = property.GetCustomAttribute(typeof(DefaultValueAttribute)) as DefaultValueAttribute;

                    modelBuilder.Entity(entityClass).Property(property.Name).HasDefaultValueSql(pAttr.Value.ToString());
                }
            }
        }
    }
}

Table.cs

//Use DataAnnotations for your properties in your classes.
[Table("CustomTableName")]
public class MyTable
{
  [Key, DefaultValue("NEWSEQUENTIALID()")]
  [Column(Order = 0)]
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
  public Guid Id { get; set; }
  
  [Column(TypeName = "datetime2(7)"), DefaultValue("SYSTEMDATIME()")]
  public DateTime LastUpdated { get; set; }
  
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
  public DateTime Created {get; set;}

  [MaxLength(15), Column(TypeName = "varchar(15)")]
  [DefaultValue("'127.0.0.1'")]
  public string ClientIp { get; set; }
}

Thank you.
This writing is very comfortable and I like it very much. If you can, please consider nullable types and other database support, such as Sqlite.

Thank you. This writing is very comfortable and I like it very much. If you can, please consider nullable types and other database support, such as Sqlite.

Thanks for the suggestion. I'll create a repo for that. Go to https://github.com/DiomedesDominguez/upgraded-enigma