从可以为空的日期时间获取日期？

Question

I have declared a field in my model as nullable datetime like this

public DateTime? CallNextDate {get;set;}

in my aspx code behind I am using this linq like this:

q = q.AsQueryable()
    .Where(c => c.CallNextDate.Date < DateTime.Now.Date )
    .ToList();

but c.CallNextDate.Date is not available. Please suggest how to fix it

Answer 1

Well, if you already know it's non-null, you can use Value to get the underlying non-nullable value:

q = q.AsQueryable()
     .Where(c => c.CallNextDate.Value.Date < DateTime.Now.Date)
     .ToList();

Or if you want to filter on that too:

q = q.AsQueryable()
     .Where(c => c.CallNextDate.Value != null &&
                 c.CallNextDate.Value.Date < DateTime.Now.Date)
     .ToList();

I'd strongly encourage you to fetch today's date once though, and reuse it for the whole query:

var today = DateTime.Today;
q = q.AsQueryable()
     .Where(c => c.CallNextDate.Value != null &&
                 c.CallNextDate.Value.Date < today)
     .ToList();

That will give you more consistency. You should really consider whether you definitely want the system local date , by the way.

(Do you definitely need to use AsQueryable , by the way? That's relatively rare.)

Answer 2

Nullable types have a Value property which represents the underlying type:

q = q.AsQueryable()
    .Where(c => c.CallNextDate.Value.Date < DateTime.Now.Date )
    .ToList();

But you will need to check to make sure the type has a value.

q = q.AsQueryable()
    .Where(c => c.CallNextDate.HasValue && c.CallNextDate.Value.Date < DateTime.Now.Date )
    .ToList();

Answer 3

To get the value you can use:

 GetValueOrDefault()

Example:

item.DOB is a nullable datetime.

item.DOB.GetValueOrDefault().Year