Why Does Entity Framework Throw 'Lambda expression with statement body cannot be converted to an expression tree'?

Error: "Lambda expression with statement body cannot be converted to expression tree" in EntityFramework

Getting the error "A lambda expression with a statement body cannot be converted to an expression tree" while using Entity Framework can be confusing. Let's clarify what the issue is and how to resolve it.

The error occurs when trying to execute a lambda expression that contains a statement body, like the one provided in the question. In Entity Framework, lambda expressions are used to build LINQ queries, which are then translated into SQL statements for database execution. However, statement bodies in lambda expressions, such as variable declarations and assignments, cannot be converted into SQL.

To fix this issue, it's recommended to use a simpler lambda expression that directly returns its values without additional statements. Here's a corrected example:

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

In this case, the lambda expression simply creates a new instance of the Obj class with the desired properties. This can be converted into an expression tree that the database can understand and execute. Remember, when working with Entity Framework, ensure that lambda expressions used in database queries are straightforward and do not contain complex statements.

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