ELSA Workflow 3.1 JsonException when adding a custom activity through the designer

ONLINECAST

2 min read

·

04-10-2024

11

0

Share

ELSA Workflow 3.1: Tackling JsonException When Adding Custom Activities Through Designer

Problem: When attempting to add a custom activity to an ELSA Workflow 3.1 process through the designer, you encounter a JsonException. This frustrating issue prevents you from seamlessly integrating your custom logic into the workflow.

Rephrased: You've created a custom activity in your ELSA Workflow project, but when you try to drag and drop it onto the workflow designer, you get an error message related to JSON. This means the designer can't recognize and use your custom activity.

Scenario: Imagine you're building a complex workflow for automating a business process. You need a specific step to perform a unique task that isn't included in ELSA's default activities. You create a custom activity class to handle this task, but when you try to add it in the designer, the dreaded JsonException appears.

Original Code Example:

// Custom Activity class
public class MyCustomActivity : Activity
{
    // ... Activity implementation ...
}

Analysis:

The JsonException usually occurs when the designer struggles to serialize your custom activity into a JSON format for internal representation. This can happen due to a few reasons:

1. Missing or Incorrect Attributes: The JsonException can occur if your custom activity class lacks necessary attributes to guide the serialization process. You need to mark the properties and methods relevant to the designer with proper attributes like JsonProperty from the Newtonsoft.Json library.

2. Circular References: If your custom activity class has circular references (e.g., two properties referring to each other), it can cause serialization issues leading to the exception. You might need to use appropriate techniques like custom JSON converters to handle these situations.

3. Missing Dependencies: Make sure all the required NuGet packages (like Newtonsoft.Json) are properly referenced in your project. The designer relies on these packages to serialize your custom activity.

Solution:

1. Add Required Attributes:

   • Decorate the properties you want to expose in the designer with the JsonProperty attribute.
   • For methods, use the JsonProperty attribute with a specific name (e.g., JsonProperty("ActionName")).

2. Resolve Circular References:

   • Use custom JSON converters to break the circular references.
   • Consider redesigning the activity to avoid circular references.

3. Verify Dependencies:

   • Ensure the Newtonsoft.Json package is installed and referenced correctly in your project.

Example:

using Newtonsoft.Json;

// Custom Activity class
public class MyCustomActivity : Activity
{
    [JsonProperty("InputValue")]
    public string Input { get; set; }

    [JsonProperty("OutputValue")]
    public string Output { get; set; }

    [JsonProperty("ActionName")]
    public string ActionName => "MyCustomAction";

    public override void Execute()
    {
        // ... Your custom activity logic ...
    }
}

Additional Value:

• Documentation: Refer to the ELSA Workflow documentation for detailed information on custom activity development and best practices.
• Community Forums: Join the ELSA Workflow community forums or Stack Overflow to seek help from other developers.

References:

• ELSA Workflow Documentation
• Newtonsoft.Json

Conclusion:

By understanding the reasons behind the JsonException and implementing the correct attributes and addressing circular references, you can smoothly add custom activities to your ELSA Workflow 3.1 projects, enabling you to build powerful and customized workflows for your business needs.