How to Resolve Entity Framework's Inability to Translate Double.Parse()?

Entity Framework Conversion Issue: Unable to Translate Double.Parse

When working with LINQ to Entities, it's important to note that not all methods supported in LINQ to Objects can be directly translated into SQL queries. One common error is the inability to use Double.Parse() in LINQ to Entities statements.

Resolving the Issue for Double.Parse()

To resolve this issue, you can define a custom method that performs the parsing and translate it to valid SQL using a function defined in the *.edmx file.

Example:

1. Define the SQL Translation:
   In the ConceptualModels section of your *.edmx file, add the following function definition:

   <function name="ParseDouble" returntype="Edm.Double">
       <parameter name="stringvalue" type="Edm.String"></parameter>
       <definingexpression>
           cast(stringvalue as Edm.Double)
       </definingexpression>
   </function>

2. Create the Custom Method in Code:

   In your ObjectContext partial class (usually generated by the EDMX), add the following method:

   public static double ParseDouble(string stringvalue)
   {
       return Double.Parse(stringvalue);
   }

   This method will serve as a stub during LINQ queries and be translated to the SQL CAST statement defined in the EDMX.

Example (Applying the Custom Method):

In your LINQ statement, replace any instances of Double.Parse() with YourObjectContext.ParseDouble() to utilize the custom method and allow translation to SQL.

Additional Considerations:

Keep in mind that Math.Round() may also require a similar approach if it's not supported by Entity Framework in the specific context. Use the EDM Canonical Functions list to determine the appropriate SQL function to define.

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