How to use Exclude in FluentAssertions for property in collection?

Simple way would be to set assertions on collection directly, combined with its exclusion on ClassA equivalency assertion:

expectedA.ShouldBeEquivalentTo(expectedB,
   o => o.Excluding(s => s.PropertyInfo.Name == "Children"));
expectedA.Children.ShouldBeEquivalentTo(expectedB.Children,
   o => o.Excluding(s => s.PropertyInfo.Name = "Id"));

There are a few valid answers here, but I am adding another one that does not involve stringly-typed expressions.

expectedA.ShouldBeEquivalentTo(expectedB, o => o.Excluding(s => s.Children));
expectedA.Children.ShouldBeEquivalentTo(expectedB.Children, o => o.Excluding(s => s.Id));

I've just come across a similar problem and the latest version of FluentAssertions has changed things a bit.

My objects contains dictionaries of other objects. The objects in the dictionaries contain other objects that I want to exclude. The scenario I have is around testing Json serialization where I ignore certain properties.

This works for me:

gotA.ShouldBeEquivalentTo(expectedB , config => 
  config
    .Excluding(ctx => ctx.SelectedMemberInfo.MemberType == typeof(Venue))
    .Excluding(ctx => ctx.SelectedMemberInfo.MemberType == typeof(Exhibit))
    .Excluding(ctx => ctx.SelectedMemberInfo.MemberType == typeof(Content))
    .Excluding(ctx => ctx.SelectedMemberInfo.MemberType == typeof(Survey))
    .Excluding(ctx => ctx.SelectedMemberInfo.MemberType == typeof(Media))
  );

Took some time to work out how to do it, but it's really useful!

What about?

expected.ShouldBeEquivalentTo(actualA, options => options.Excluding(su => 
   (su.RuntimeType == typeof(ClassB)) && (su.PropertyPath.EndsWith("Id")));`

Or you could do a RegEx match on the property path, such as

expected.ShouldBeEquivalentTo(actualA, options => options.Excluding(su => (Regex.IsMatch
   ("Children\[.+\]\.ID"));

I actually like that last one, but the regex stuff makes it a bit difficult to read. Maybe I should extend ISubjectInfo with a method to match the path against a wildcard pattern, so that you can do this:

expected.ShouldBeEquivalentTo(actualA, options => options
  .Excluding(su => su.PathMatches("Children[*].ID")));