Why Can't I Convert a Lambda Expression with a Statement Body to an Expression Tree in Entity Framework?

"Understanding the "A lambda expression with a statement body cannot be converted to an expression tree" Error in EntityFramework"

The "A lambda expression with a statement body cannot be converted to an expression tree" error occurs when attempting to convert a lambda expression with a statement body to an expression tree. This error commonly arises in Entity Framework scenarios, where LINQ queries are used to retrieve data.

One possible cause for this error is when Linq-To-SQL is used, where only simple expressions can be applied to the immediate right of the => operator. The reason for this limitation is that these expressions are not executed but are directly translated to SQL queries.

As a solution to this issue, refactor the lambda expression to exclude statement bodies. For instance, rewrite the following code:

Obj[] myArray = objects.Select(o =>
{
    var someLocalVar = o.someVar;

    return new Obj() { 
    Var1 = someLocalVar,
    Var2 = o.var2 };
}).ToArray();

To the following:

Arr[] myArray = objects.Select(o => new Obj() { 
    Var1 = o.someVar,
    Var2 = o.var2 
}).ToArray();

This modification removes the statement body, enabling the conversion of the lambda expression to an expression tree and eliminating the error.

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