Cannot convert anonymous type to expression tree because it contains a field that is used in the initialization of another field

  • Article

The compiler does not accept conversion of an anonymous to an expression tree when one property of the anonymous type is used to initialize another property of the anonymous type. For example, in the following code, Prop1 is declared in the initialization list and then used as the initial value for Prop2.

Module M2

    Sub ExpressionExample(Of T)(ByVal x As Expressions.Expression(Of Func(Of T)))
    End Sub

    Sub Main()
        ' The following line causes the error.
        ' ExpressionExample(Function() New With {.Prop1 = 2, .Prop2 = .Prop1})

    End Sub
End Module

Error ID: BC36548

To correct this error

  • Assign the initial value for Prop1 to a local variable. Assign that variable to both Prop1 and Prop2, as shown in the following code.

    Sub Main()

    Dim temp = 2
    ExpressionExample(Function() New With {.Prop1 = temp, .Prop2 = temp})

End Sub

See Also

Tasks

How to: Use Expression Trees to Build Dynamic Queries

Concepts

Anonymous Types

Expression Trees in LINQ