LinqKit System.InvalidCastException When Invoking method-provided expression on member property

Question

Given a simple parent/child class structure. I want to use linqkit to apply a child lambda expression on the parent. I also want the Lambda expression to be provided by a

Answer 1

var lambdaX = Bar.GetLambdaX();

Expression<Func<Foo, bool>> lx = c => lambdaX.Invoke(c.Bar);

This works.

Be careful with writing

Expression<Func<Foo, bool>> lx = ...

Before assignment the compiler processes this line and in your case creates a Method Call Expression (i.e. for calling Bar.GetLambdaX()) that is assigned to lx.

If you use var ... then Bar.GetLambdaX(); is called and assigned, the value of which (which is the lambda expression) is used later in lx = ...