Why Does LINQ to Entities Fail to Translate `ToString()` and How Can I Fix It?

LINQ to Entities: Addressing the ToString() Method Translation Issue

The Problem:

Executing a LINQ to Entities query incorporating the ToString() method often results in an error: "LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression." This occurs because ToString() isn't directly translatable into SQL.

The Root Cause:

Entity Framework (EF) translates LINQ queries into SQL for database execution. Since ToString() is a .NET method, not a SQL function, the translation process fails.

The Solution:

The most reliable solution is to avoid calling ToString() directly within the LINQ query. Instead, store the result of ToString() in a variable before using it in your query. This allows EF to properly translate the query.

string strItem = item.Key.ToString();

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

Alternative in EF Core:

Newer versions of EF Core provide the SqlFunctions.StringConvert method, offering a more direct approach for string conversions within LINQ queries, often eliminating the need for temporary variables. However, the variable approach remains a robust and widely compatible solution.

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