Question

I have a simple LINQ query. I would like to only check the DateDisable if there is an entry in the database. If the user doesn’t select a date to disable the entry will always show. Can someone please show me how to add a conditional statement within linq

return (from promo in context.Promoes
        where promo.DateEnable <= DateTime.Today
        where promo.DateDisable >= DateTime.Today
        orderby promo.SortOrder
        select promo).ToList();

Answer 1

Given that DateEnable is a DateTime?, you can do the following:

// Get today.
DateTime today = DateTime.Today;

return (
    from promo in context.Promoes
    where 
        promo.DateEnable <= today &&
        (promo.DateDisable == null || promo.DateDisable >= today)
    orderby promo.SortOrder
    select promo
).ToList();

Basically, you need to check for null or whether or not the date is greater than today.

Also you should capture the value outside of the statement, it’s not guaranteed that the the LINQ provider will translate DateTime.Today on the database side correctly.

However, be warned that because of deferred execution, if you wait a long time to execute the query, today might not give you the value you expect (if the time between declaring the query and executing it rolls past midnight).

Of course, if your database server is in a different timezone than your application server, then you’ll need to ensure that DateTime.Today is handled by your LINQ provider correctly (so that it’s executed on the server) and use that if you want to compare against time on the DB server. If your provider doesn’t handle translating DateTime.Today correctly, then you’ll have to resort to a stored procedure and call that.