Bug: Elsa 2.0 MongoDb Deserializing

When loading workflow instances I get the following error.

An error occurred while deserializing the Activities property of class Elsa.Models.WorkflowInstance: An error occurred while deserializing the Output property of class Elsa.Models.ActivityInstance: Unknown discriminator value 'FinishOutput'.

I already know the cause of this: https://stackoverflow.com/a/43312423

BsonClassMap.RegisterClassMap<FinishOutput>(); will fix the problem.

But it will probably happen more often. It would be best to register the classes centrally, so that in Elsa.Persistence.MongoDb only the central place has to be read and thus no dependencies to other projects exist.

I just don’t know yet where it is nicest and how to name it best.

[sfmskywalker]

@Juandavi1 This should be fixed with the latest preview packages available on MyGet and of course in master. Please feel free to reopen if you can still reproduce this issue with the latest version and repro steps. Thanks!

[sfmskywalker]

Tricky problem, here’s why:

• When using MongoDB, we need to register any and all types that are potentially stored in a workflow instance using BsonClassMap.RegisterClassMap<T>.
• We have many modules with activities that potentially store something within a workflow instance.
• None of these modules should have a dependency on MongoDB.
• The MongoDb provider itself should also not have a dependency on any of the activity modules (such as Elsa.Activities.Http).

One not-so-great solution I can think of is to require the host application to register these types, like so:

public class Startup
{
    public Startup()
    {
        BsonClassMap.RegisterClassMap<HttpRequestModel>(cm => cm.AutoMap());
    }
}

Which is far from ideal of course, because now the user needs to understand what types to register, depending on what activity packages they use.

So what we might do instead is let Newtonsoft.Json take care of object serialization, which does not require “known types” to be registered.

I tried it and it works wonders, but it also means that it will break existing MongoDB databases where they basically need to wipe their DB.