LINQ criteria question

[joewmaki]

I can generate simple LINQ queries using a listbox as criteria:

Dim Result = From person in db.Persons _
                           Where Person.id = Me.ListBox1.Text _
                           Select Person.Name, Person.Phone

Is there any way to reference the listbox.SelectedItems or something similar in a multiselect listbox?

[Phil Weber]

Try this:

Dim Result = From person in db.Persons _
                   Where ListBox1.SelectedItems.Contains(Person.id) _ 
                   Select Person.Name, Person.Phone

[joewmaki]

Throws an error here:

System.NotSupportedException - Method 'Boolean Contains(System.Object)' has no supported translation to SQL

I notice LINQ does not support the IN SQL clause either.

[joewmaki]

Ok, I got something to work:

Dim Criteria = From item in ListBox1.SelectedItems

Dim Result = From person in db.Persons _
                           Where Criteria.Contains(Person.id) _
                           Select Person.Name, Person.Phone

I haven't been able to reference the listbox directly in the criteria.

[Phil Weber]

Hmm. My syntax could be wrong, but Contains should work. See if this helps: http://www.google.com/search?q=linq+sql+%22in+clause%22

[joewmaki]

Ok, I got something to work:

Dim Criteria = From item in ListBox1.SelectedItems

Dim Result = From person in db.Persons _
                           Where Criteria.Contains(Person.id) _
                           Select Person.Name, Person.Phone

I haven't been able to reference the listbox directly in the criteria.

This works, but I think the previous syntax is easier to maintain:

Dim Result = From person in db.Persons _
                 Where (From item in ListBox1.SelectedItems).Contains(Person.id) _
                 Select Person.Name, Person.Phone

[Hack]

This works, but I think the previous syntax is easier to maintain:

I'm curious as to why you think it would be easier to maintain.

They both look pretty self-explanatory.

[joewmaki]

Your probably right I just need to get used to the LINQ syntax.

[Hack]

Your probably right I just need to get used to the LINQ syntax.

Yeah, you and me both. But, we will get there.

[joewmaki]

I did some simple timing tests and the first method is consistantly about 30% faster than embedding the subquery.