Question

I’d like to order my list by a string converted into an int:

var orderedListOfRfidTags = uow.RfidTags.OrderBy(t => Convert.ToInt32(t.Number)).ToList();

but get: The method ‘ToInt32’ is not supported.

Answer 1

I am one of the developers of LightSpeed.

The LINQ provider in LightSpeed 3.11 RTM doesn’t support Convert.ToInt32. However we have now added support via a nightly release which is available for download now.

If you don’t want to use the nightly release, you can achieve the result you want by dropping down to the Query Objects API and invoking the SQL CAST function directly. This will look something like:

Query query = new Query
{
  Order = Order.By(Entity.Attribute("Number")
                         .Function("CAST", new LiteralExpression("INTEGER") { EmitInline = true }))
};

uow.Find<RfidTag>(query);

The reason for the rather verbose LiteralExpression for the cast type is that by default LightSpeed sends values to the database through parameters (to avoid SQL injection attacks). But for the CAST function the SQL engine needs to see CAST(Number, INTEGER) rather than CAST(Number, @p0) where p0 has the value “INTEGER”. So you have to use an EmitInline expression, which bypasses parameterisation, rather than the more natural string literal.

Once again, though, the nightly release does support Convert.ToInt32 in LINQ so you only need to drop down to this level if you want to avoid taking a nightly build.