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

Error: "A lambda expression with a statement body cannot be converted to an expression tree" when using EntityFramework

When using EntityFramework's Select method, you may encounter the error: "A lambda expression with a statement body cannot be converted to an expression tree." This error often occurs when the lambda expression you provide contains a statement body instead of a simple expression.

Understanding the Error:

In the provided code snippet:

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

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

The lambda expression uses a statement body to declare and use a local variable someLocalVar before returning an instance of Obj. However, EntityFramework expects simple expressions that can be directly translated into SQL for efficient database execution.

Solution:

To resolve this error, simplify the lambda expression by removing the statement body and assigning the values directly:

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

With this modification, the lambda expression only contains a simple expression that can be translated into an expression tree, and the code will compile successfully.

The above is the detailed content of Why Does Entity Framework Throw 'A lambda expression with a statement body cannot be converted to an expression tree'?. For more information, please follow other related articles on the PHP Chinese website!