store only date in database not time portion C#

I think you are trying to specify database column type. You could use data annotations as described in this article.

Here is an example :

[Table("People")]
public class Person
{
    public int Id { get; set; }

    [Column(TypeName = "varchar")]
    public string Name { get; set; }

    [Column(TypeName="date")]
    public DateTime DOB { get; set; }
}

By default, string is translated to nvarchar, we have changed that here. Also Datetime (this is what you asked I suppose) which by default maps to datatime in sql server, is changed to date which stores only the date portion and not the time portion of a DateTime value.