How can I convert from Expression<Func<TSource, TSourceMember>> to Func<TSource, bool> condition

0
votes

I am trying to convert from

x => x.SomeProperty

to

x => x.SomeProperty is ISomeInterface

In a method that fits the following signature:

Func<TSource, bool> Convert(Expression<Func<TSource, TSourceMember>> source);

Where SomeProperty might be a collection or a single object. Can anyone help?

I'm finding it difficult to work out what kind of expressions these are. I think that the first one is a MemberExpression and the second is a UnaryExpression.

I'd be happy to move the

x.SomeProperty is ISomeInterface

logic into a method if that would make things easier.

bool IsSomeInterface(object obj)
{
  return obj is ISomeInterface;
}

Any pointers or tutorials on how to put this stuff together would be appreciated. I always seem to struggle with Expression trees.

1
c#lambdalinq-expressions

1 Answers

2
votes

You might be looking for Expression.TypeIs(...). Try this:

    Func<TSource, bool> Convert<TSource, TSourceMember>(Expression<Func<TSource, TSourceMember>> source)
    {
        return (Func<TSource, bool>)(Expression.Lambda<Func<TSource, bool>>(Expression.TypeIs(source.Body, typeof(ISomeInterface)), source.Parameters).Compile());
    }