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I have the following LINQ Query. Note that DataValue is a string value. I am trying to convert it to a float and then get the average. 

var Avg = (from fd in DataContext.FormData
           select float.Parse(fd.DataValue)).Average();

I get the following error:

System.NotSupportedException: 'LINQ to Entities does not recognize 
the method 'Single Parse(System.String)' method, and this method 
cannot be translated into a store expression.'

Is there a good work around to this issue?

AustinWBryan
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Nate Pet
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    Either select the data into memory and then convert the values in an `IEnumerable` or write a custom SQL query to do the conversion and average. – Dan Wilson May 16 '18 at 20:49

2 Answers2

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You should be able to use Convert.ToSingle instead of float.Parse:

var Avg = DataContext.FormData
    .Select(fd => DataContext.FormData(fd.DataValue))
    .Average();
Sergey Kalinichenko
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Not every C# function is a mapped function to SQL. Depending on the ORM you are using (I'm assuming EntityFframework), you can find a list of mapped functions in the ORM documentation.

Mapped function basically mean a C# function that the ORM maps/converts to an SQL function and add it to the end result SQL statement that gets executed by the ORM.

Read the documentation to be safe.

If you still want to use Float.Parse, then your only option is to materialize the query first then Parse, then Average. But that is not recommended.

Tarek
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  • `Convert.ToFloat` is not a valid function. It's `Convert.ToSingle` and this function isn't mapped to. – H. Pauwelyn Nov 18 '19 at 11:03
  • Thanks for the information, I wasn't sure what it was when I wrote the answer. But advised the person who asked to check the docs themselves. – Tarek Nov 18 '19 at 12:10