returning a single row from a table

Question

User172691333 posted

Hi,

I found this two way of returning a single row from my a table, is there anybody who can explain their difference to me?

A)            Test selectedTest = Context.Tests.Single(t => t.ID == ID);

B(             Test selectedTest = (from T in Context.Tests
                                     where T.ID == ID
                                     select T).SingleOrDefault();

Answer 1

User533502567 posted

For following code: You will get default item if no records exists in the table

B(             Test selectedTest = (from T in Context.Tests
                                     where T.ID == ID
                                     select T).SingleOrDefault();

For following code: You will get exception if no records exists in the table.

        Test selectedTest = Context.Tests.Single(t => t.ID == ID);

When the sequence contains many elements(more than one) -- You will get an exception in both cases.

If you want one record no matter what the sequence contains, use FirstOrDefault.

Answer 2

User172691333 posted

Thanks a lot budugu for the clarification.

 I actually tried both in a context and I got different errors for each.

I posted another another question a minut ago explaining the context, It will be great if you can help me with that too.

The subject is: "Object reference not set to an instance of an object / Sequence contains no elements ??"

Thanks again,

Kia

Answer 3

User-271186128 posted

Hi Kia,

kia997997

The subject is: "Object reference not set to an instance of an object / Sequence contains no elements ??"

As for this issue, I suppose the query result is null, please check your database and make sure it contains the specify records.

You could add a IF Else statement to check the result, like  this:

                Test selectedTest = (from T in Context.Tests
                                    where T.ID == ID
                                    select T).SingleOrDefault();
                if(selectedTest != null)
                {
                    selectedTest.ID = ID;
                    selectedTest.Stat = "Deleted";
                    Context.SubmitChanges();
                }

Best regards,
Dillion