Using SQRT in a Linq EF Query

Question

I need to use the SQRT function as part of a where clause in a Linq EF query. I figured I could do this:

var qry = context.MyTable.Where("sqrt(it.field) > 1");

But it returns an error saying "'sqrt' cannot be resolved into a valid type constructor or function., near function, method or type constructor, line 6, column 5."

I had always assumed that linq literally takes what's in the where clause and translates that into a statement that is executed directly in SQL. That doesn't seem to be the case...

Anyone know the work-around?

Thanks

Answer 1

I'm using Linq Entities and was able to do this:

        testEntities entities = new testEntities ();

        ObjectQuery<Fees> fees = entities.Fees;

        return from f in fees 
               let s = Math.Sqrt((double)f.FeeAmount)
               where s > 1.0 
               select f ;

When I check the generated SQL, I get

SELECT [t1].[TestTriggerID]
FROM (
    SELECT [t0].[TestTriggerID], SQRT(CONVERT(Float,[t0].[TestTriggerID])) AS [value]
    FROM [TestTrigger2] AS [t0]
    ) AS [t1]
WHERE [t1].[value] > @p0

This seems reasonable. I was unable to use the .Where string format to reproduce the same code, but I'm probably missing something obvious.

Answer 2

I don't know how you got your answer working against EF. When I tried it with EF4, it wouldn't work for me. I'd get:

LINQ to Entities does not recognize the method 'Double Sqrt(Double)' method, and this method cannot be translated into a store expression.

So after banging my head against this for a while (after all, Math.Pow(double) is supported, and SQRT is available in SQL), I realised that the square root of a value is the same as its power of a half.

So, this solution works fine.

from e in context.MyEntities
     let s = Math.Pow(e.MyDouble, 0.5)
     select s;

The generated SQL uses POWER instead of SQRT:

SELECT 
POWER( CAST( [Extent1].[MyDouble] AS float), cast(0.5 as float(53))) AS [C1]
FROM [dbo].[MyEntities] AS [Extent1]

A simple enough workaround to a daft problem. Hope this helps someone else out.

Answer 3

Check the msdn document.Entity sql doesn't support the sqrt function.

Answer 4

You can use System.Data.Entity.SqlServer.SqlFunctions.SquareRoot as of EF6.