如何在Entity Framework中使用DateTime.AddDays(x)

Question

我有这个代码:

from pr in e.ProgramSetup.Include("Program").Include("Program.Client")
        where pr.DateBegin < DateTime.Now
        && pr.DateEnd > DateTime.Now.AddDays(pr.DateEndOffset) 
select pr).ToList();

它不起作用,因为无法使用AddDays()来生成sql.

还有另一种方式吗？现在我选择所有内容并通过foreach最终过滤它,但在我看来这不是好方法.

问题是pr.DateEndOffset也只在db中,它不是常量...

Answer 1

您需要使用映射到规范函数的EntityFunction之一.以下是AddDays的示例:

public class MyEntity
{
    public int Id { get; set; }
    public DateTime Date { get; set; }
}

public class MyContext : DbContext
{
    public DbSet<MyEntity> Entities { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        using (var ctx = new MyContext())
        {
            if (!ctx.Entities.Any())
            {
                ctx.Entities.Add(new MyEntity() { Date = new DateTime(2000, 1, 1) });
                ctx.Entities.Add(new MyEntity() { Date = new DateTime(2012, 10, 1) });
                ctx.Entities.Add(new MyEntity() { Date = new DateTime(2012, 12, 12) });
                ctx.SaveChanges();
            }

            var q = from e in ctx.Entities
                    where e.Date > EntityFunctions.AddDays(new DateTime(2012, 10, 1), 10)
                    select e;

            foreach (var entity in q)
            {
                Console.WriteLine("{0} {1}", entity.Id, entity.Date);
            }
        }
    }
}

Answer 2

using System.Data.Entity;
...
DbFunctions.AddDays(dateFromDataStore, numDaysToAdd);