Make Math.Log work in an Entity Framework Query

Question

How can I make this orderby code work thisEntity Framework query

This is the orderby part of the query

orderby (double)b.score * Math.Pow( (1 + Math.Log(b.total_votes)), 0.2)

I get this exception:

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

How can I make it work?

If you don't need the sorting to happen in the db, you can just call `ToList()` to fetch the results before sorting. — Lorentz Vedeler, Sep 16 '16 at 07:59
I am not working with math for a long time, but I am just wondering, why to use this complex ordering? If I am not mistaken `a*b` is always greater than `a * Math.Pow((1 + Math.Log(b)), 0.2)`, no matter how you change the `a` and `b`. So you will get same results if you simply order by `a*b`. Please correct me, if I miss something — Adil Mammadov, Sep 16 '16 at 08:17
@IdanShechter cheked myself, there can be differences. You can look at fiddle test [here](https://dotnetfiddle.net/30jBFv). — Adil Mammadov, Sep 16 '16 at 08:44

sachin · Accepted Answer · 2016-09-16T08:23:22.910

2

Entity Framework tries to translate Math.Log function into SQL so that it could be executed against the DB but it doesn't know how to do that for Math.Log.

One solution is to retrieve all your items into memory using .ToList(), and execute Math.Log in memory using LINQ to Objects.
Another solution is to use the existing SqlFunctions.Log.

This is how you could write your orderby:

orderby (double)b.score * Math.Pow((1 + SqlFunctions.Log(b.total_votes) ?? default(double)), 0.2)

And if there are just 10 records, this is how you can sort in memory:

from b in _dataContext.MyTypes.ToList() orderby (double)b.score * Math.Pow((1 + Math.Log(b.total_votes)), 0.2) select b;

edited Sep 16 '16 at 08:23

answered Sep 16 '16 at 08:11

sachin

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what is the type of total_votes? Try casting b.total_votes to double. – sachin Sep 16 '16 at 08:20
I cast to double and after I run the code, I get this exception: The specified method 'System.Nullable`1[System.Double] Log(System.Nullable`1[System.Double])' on the type 'System.Data.Entity.SqlServer.SqlFunctions' cannot be translated into a LINQ to Entities store expression. My code: orderby (double)b.score * Math.Pow((1 + System.Data.Entity.SqlServer.SqlFunctions.Log((double)b.total_votes) ?? default(double)), 0.2). Total Votes is of type long. – Liron Harel Sep 16 '16 at 08:21
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I think you can go with 2nd approach as you're saying that there are only 10 records. – sachin Sep 16 '16 at 08:24
what .MyTypes.ToList() means? – Liron Harel Sep 16 '16 at 08:40
The returned results is a new type (I made a class for it called sortedResults) – Liron Harel Sep 16 '16 at 08:42
I was using MyTypes for a placeholder as I didn't know your type :) – sachin Sep 16 '16 at 09:13

score 0 · Answer 2 · edited May 23 '17 at 11:45

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There are a lot of same questions: this, that, etc. Try to use SqlFunctions.Log

edited May 23 '17 at 11:45

Community

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answered Sep 16 '16 at 08:08

Alexander

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Make Math.Log work in an Entity Framework Query

2 Answers2