C＃ASP.NET MVC 4中的DateTime.Now

Question

I have created a model for Articles, and in the articles I am trying to implement a date created on initial create.

//Model

    [Display(Name = "Date Created")]
    public DateTime dateCreated
    {
        get { return DateTime.Now; }
    }

It works well when I create an article, but it also sets the same date time value to all the other articles. :/

Is there a way around this?

cheers.

Answer 1

Putting that in a property will evaluate the DateTime.Now each time the property is accessed, so if you query it twice, you'll get two different values.

There are a number of possible options for modeling this, but normally you'll want a read-only property set-ed in the constructor:

public Article()
{
    This.DateCreated = DateTime.Now;
}

[Display(Name = "Date Created")]
public DateTime DateCreated {get; private set;}

Answer 2

It works well when I create an article, but it also sets the same date time value to all the other articles.

This is exactly why it is a bad idea. Get what you do is exposing the current date and time with that property.

Why can't you set it right before you save your changes?

For instance:

public override int SaveChanges()
{
  DateTime saveTime = DateTime.Now;
  foreach (var entry in this.ChangeTracker.Entries().Where(e => e.State == System.Data.EntityState.Added))
   {
     if (entry.Property("dateCreated").CurrentValue == null)
       entry.Property("dateCreated").CurrentValue = saveTime;
    }
    return base.SaveChanges();

}

Answer 3

Here's what you need:

private DateTime? dateCreated;
public DateTime DateCreated
{
    get { return dateCreated ?? DateTime.Now; }
    set { dateCreated = value; }
}

What this does is wait until this property is first accessed. Then, it will see if a created date has already been set and if not, it will set it to DateTime.Now . For initial creates, this will usually happen when EF attempts to save it to the database, which is exactly when you want that to happen. It would only happen sooner if you tried to manually access the property before saving, but there's no good reason why you would do that. The set method just allows a normal set, so when EF pulls this from the database, it will just set the private field and it will always be set to that.