CreatedAt property with Entity framework

Jun 15, 2016

You’re building a new application, and you’re using Entity Framework Code First. Probably all your entities need an Id and CreatedAt/UpdatedAt property.

The sample below shows you how to define these properties in a base class, and (more importantly) how to set them correctly on every save, without setting them manually on every place where you’re changing things.

We do this by overriding the SaveChanges method of the DbContext.

    [Table("Blogs")]
    // We inherit the EntityBase class here (with Id, CreatedAt and UpdatedAt)
    public class Blog : EntityBase
    {

        [MaxLength(150)]
        [Required]
        public string Name { get; set; }
        
        [Required]
        [DataType(DataType.MultilineText)]
        public string Text { get; set;}
    }

    public class BlogsDatabase : DbContext
    {
        public InternshipDatabase() : base("BlogsDB") { }
        public DbSet<Blog> Blogs { get; set; }

        // Lets override the default save changes, so we automaticaly change the UpdatedAt field.
        public override int SaveChanges()
        {
            foreach (var entry in ChangeTracker.Entries().Where(x => x.Entity.GetType().GetProperty("CreatedAt") != null))
            {
                if (entry.State == EntityState.Added)
                {
                    entry.Property("CreatedAt").CurrentValue = DateTime.Now;
                }
                else if (entry.State == EntityState.Modified)
                {
                    // Ignore the CreatedTime updates on Modified entities. 
                    entry.Property("CreatedAt").IsModified = false;
                }
                // Always set UpdatedAt. Assuming all entities having CreatedAt property
                // Also have UpdatedAt
                entry.Property("UpdatedAt").CurrentValue = DateTime.Now;
            }
            return base.SaveChanges();
        }
    }

    public class EntityBase
    {
        [Key]
        public Guid Id { get; set; } = Guid.NewGuid();
        public DateTime? CreatedAt { get; set; } = DateTime.Now;
        public DateTime? UpdatedAt { get; set; } = DateTime.Now;
    }

I hope you like my sample, so please let me know below or share this post on social media.