Why Does LINQ to Entities Throw a 'System.String ToString()' Exception During MySQL to SQL Server Migration?

Troubleshooting the 'System.String ToString()' LINQ to Entities Exception

During database migration from MySQL to SQL Server, using LINQ to Entities might trigger this error:

<code>LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression.</code>

This happens because LINQ to Entities lacks a direct SQL equivalent for the ToString() method.

Resolution

The solution involves pre-processing the string conversion:

<code class="language-csharp">var strItem = item.Key.ToString();

IQueryable<entity> pages = from p in context.pages
                           where p.Serial == strItem
                           select p;</code>

By performing ToString() beforehand, the conversion happens in memory, outside the database query.

Additional Considerations:

• For newer Entity Framework Core versions, consider using the SqlFunctions helper class for SQL-compatible string conversions.
• Sometimes, ToString() is redundant. Direct comparison might suffice, eliminating the error entirely.

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