PreserveReference and "An item with the same key has already been added." ArgumentException

[nsgaga]

I'm having an issue with PreserveReference, I worked around it and I pretty much stopped using it, but I'd like to know if I'm missing something (which is likely).

• so, when I have circular references PreserveReference didn't resolve that for me

• and when I have (what seems as, it's hard to trace it, I didn't debug it with Mapster source, will do if needed) 2 properties pointing to the same object reference - then I get the above error (which is a typical dictionary/hash issue somewhere inside the Mapster code).

• so it's simple hierarchy that I'm trying to map (basically entities to view-models, pretty typical), no circular references (I made sure of that, the code is quite mature)

• what it's supposed to actually handle (2 properties pointing to the same object) is when it fails (that error)

• as soon as I remove the PreserveReference all is working (just not preserved references of course)

I'll try and dive deeper into this, provide a sample solution etc.,
but I just wanted to see if this is a known issue, or even if you ever encountered it, or it's something specific to my data/code.

[chaowlert]

Hi,

I tried to reproduce, but it works fine. Could you pls provide reproducible code?

public class ParentPoco
{
    public ChildPoco Child1 { get; set; }
    public ChildPoco Child2 { get; set; }
}
public class ChildPoco
{
    public Guid Id { get; set; }
}
public class ParentDto
{
    public ChildDto Child1 { get; set; }
    public ChildDto Child2 { get; set; }
}
public class ChildDto
{
    public Guid Id { get; set; }
}
class Program
{
    static void Main(string[] args)
    {
        TypeAdapterConfig.GlobalSettings.Default.PreserveReference(true);
        var child = new ChildPoco {Id = Guid.NewGuid()};
        var poco = new ParentPoco {Child1 = child, Child2 = child};
        var result = poco.Adapt<ParentDto>();
        Console.WriteLine(result.Child1 == result.Child2); //true
    }
}

[nsgaga]

thanks on your response,
I thought it wasn't simple issue,
I certainly will sit down and make a small project - it's part of a larger scenario, but I'll figure something out.
This is how I'm using it, as a start only (that's the offending code)

    config.NewConfig<ISomeEntity, SomeViewModel>()  
        .ConstructUsing(entity => container.Resolve<SomeViewModel.Factory>()(entity))  
        .IgnoreAttribute(typeof(DoNotMapAttribute))  
        .IgnoreNullValues(true)  
        .PreserveReference(true);

...but I should know better, I'll provide an example.
I basically just wanted to get a first response to see if it's worth investing time into it.

[chaowlert]

I have no clue why PreserveReference doesn't work in your case. Mapster checks item not exists before adding new item to dictionary. My guess is there might be some other issues that cause the problem.

[nsgaga]

And just to update, I didn't have enough time but I figured out where the problem is, roughly, I have hierarchical data structure and I was applying TypeAdapter.Adapt redundantly at every level, i.e. not just on the root but also on each child (building, again, it's own hierarchy). If I de-duplicate that and just have one mapping on the root (that takes care of the entire hierarchy) the issue goes away. Exception is somewhere within the expressions created, but it's hard to debug those.
That isn't wrong though per se (even though arguably that wasn't the best design decision on my part), and I'm guessing it should not throw.
I'm going to write a small unit test with some sample data that mimics the above case - and will post that - but need a bit more time to find some space to do it. So I didn't forget about it!

[chaowlert]

Hi, even I don't know root cause of this problem. I changed from Dictionary.Add to Dictionary[key] when adding new references to solve this issue. If you can provide test case, I'm happy to inspect the problem. I will close this issue for now.