在Linq-to-SQL查询中返回null或对象

Question

When I'm looking for a record that is mapped to an object model, I have something like this:

var Output = (from x in MyDC.SomeTable
              where  ....
              select new SomeObjectModel()
              {
                 SomeProp = x.SomeColumnField

              }.Single();

Now, I want to return on object but only if the object was found I'm doing this:

var Output = (from x in MyDC.SomeTable
              where ....
              orderby x.SomeTime descending
              select s).FirstOrDefault();

This tells me if the object was found and from there, I want to be able to retrieve SomeObjectModel() and fill in its properties but only if there's an element that was found with the . FirstOrDefault() statement and combine all this into one query. I tried adding a Select after .FirstOrDefault() but it doesn't work.

Thanks for your help.

Answer 1

Use FirstOrDefault with your first version. You can also use SingleOrDefault if you are expecting only a single item or null.

var Output = (from x in MyDC.SomeTable
              where  ....
              select new SomeObjectModel()
              {
                 SomeProp = x.SomeColumnField

              }.SingleOrDefault(); //if only single item is expected or null

return Output;

Answer 2

var OutputAsModel = (from x in MyDC.SomeTable
where ....
orderby x.SomeTime descending
select s).Select(o=>new SomeObjectModel(o)).FirstOrDefault();