Can I use C# string interpolation with Linq to SQL

Question

While using EF (up to version 6.1.3 at least) assuming you have a class like this:

 class Customer
 {
      public string FirstName { get; set; }
      public string LastName { get; set; }
 }

if you to get a field FullName that is the concatenation of both (FirstName and LastName) as a field in query result you would have to do something like this:

db.Customers.Select(c => new { FullName = c.FirstName + " " + c.LastName })

now that there is String Interpolation in C# could you do something like this instead

db.Customers.Select(c => new { FullName = $"{c.FirstName} {c.LastName}" })

this might seem like a trivial example (which it is) but the question remains.

Can I use this out of the box, do I need to make some tricks to get it working or is it sure it won't work?

Answer 1

I wouldn't expect so, no. It'll compile down to a string.Format call, which I wouldn't expect to be supported. If you really need the projection to be done in the SQL part, you could test it... but otherwise, as normal, use AsEnumerable() when you've finished the part of the query you need to be performed in the database, and then use Select after that:

var query = db.Customers
              // Project to just the properties we need
              .Select(c => new { c.FirstName, c.LastName })
              // Perform the rest of the query in-process
              .AsEnumerable()
              .Select(c => $"{c.FirstName} {c.LastName}");

Answer 2

could you do something like this instead

Not in the general sense, because string interpolation is just translated to a string.Format call, replacing the placeholders with numbers and passing the values as parameters. So your format gets translated from

$"{c.FirstName} {c.LastName}" 

to

string.Format("{0} {1}", c.FirstName, c.LastName);

Since not all functionality of string.Format() (custom format strings, padding, justification, etc) can be directly translated to SQL, it is not supported.

do I need to make some tricks to get it working or is it sure it won't work?

I doubt there are any tricks you can do to get it to work in Ling-to-SQL since you are dealing with string.Format internally. You could retrieve all of the pieces you need, call AsEnumerable to change the context from Linq-to-SQL to Linq-to-Objects, and then use interpolation in a subsequent projection, but in this trivial case using string concatenation is cleaner.