ForEach only works for the first item

Hi,

I’ve been trying to get a for-each loop to work that just writes the items of a list to the console.

The Dummy Data Generator returns a List<Dictionary<string, string>> as Output.

I use Javascript: (input) for both the ForEach Items param and the WriteLine Text param.

The expected outcome is that all my list entries are printed to the console, but what actually happens is that the first entry is successfully printed and then an exception is thrown:

Hopefully somebody can help me with this 😃

[sfmskywalker]

I see now. The issue is the use of the input variable, which changes over time.

For example, initially, input will hold the list of dictionaries (the output of the custom activity). Next, as the ForEach activity executes, it changes the input value to the item of the current iteration (a dictionary).

Once an iteration completes, ForEach is executed again, which will re-evaluate its Items property. But since this expression uses input, it is no longer the original list of dictionaries.

To fix this, you need to perform the following steps:

1. Update your custom activity by adding an output property (call it e.g. Output).
2. Then, instead of setting context.Output, set the result to the new Output property.
3. Update the ForEach items JS expression to: activities.TestDataSource1.Output().
4. Remove the connection between the WriteLine and the ForEach activity; Elsa will automatically execute the ForEach activity for you after its Iterate branch completes.

Here is the updated activity code:

[ActivityAttribute(
    Category = "Data Source",
    DisplayName = "Test",
    Description = "Fetch dummy data.",
    Outcomes = new[] { OutcomeNames.Done }
)]
public class TestDataSource : Activity
{
    [ActivityInput(Hint = "Number of entries")]
    public int EntryAmount { get; set; }

    [ActivityInput(Hint = "Number of columns")]
    public int Columns { get; set; }

    // Added.
    [ActivityOutput] public IList<Dictionary<string, object>> Output { get; set; } = default!;

    protected override IActivityExecutionResult OnExecute(ActivityExecutionContext context)
    {
        try
        {
            var result = new List<Dictionary<string, object>>();
            for (int i = 0; i < EntryAmount; i++)
            {
                var entry = new Dictionary<string, object>();
                for (int j = 0; j < Columns; j++)
                {
                    entry.Add($"key{j + i * 10}", $"value{j + i * 10}");
                }

                result.Add(entry);
            }

            // Updated.
            Output = result;

            return Done();
        }
        catch (Exception e)
        {
            throw new ActivityException("Creating Test data failed!", e);
        }
    }
}

And here is the updated workflow JSON:

{
  "$id": "1",
  "definitionId": "f78b6f6a0e554c5fbca44fb5bee0c321",
  "versionId": "91e42f8754a949b6aa5e64b1f2f92c96",
  "name": "loop_test_data",
  "displayName": "Loop test data",
  "version": 5,
  "variables": {
    "$id": "2",
    "data": {}
  },
  "customAttributes": {
    "$id": "3",
    "data": {}
  },
  "isSingleton": false,
  "persistenceBehavior": "WorkflowBurst",
  "deleteCompletedInstances": false,
  "isPublished": true,
  "isLatest": true,
  "activities": [
    {
      "$id": "4",
      "activityId": "32e64fb2-94ad-40a0-9f4e-2d6f1df771d9",
      "type": "TestDataSource",
      "name": "TestDataSource1",
      "displayName": "Test",
      "persistWorkflow": false,
      "loadWorkflowContext": false,
      "saveWorkflowContext": false,
      "properties": [
        {
          "$id": "5",
          "name": "EntryAmount",
          "expressions": {
            "$id": "6",
            "Literal": "50"
          }
        },
        {
          "$id": "7",
          "name": "Columns",
          "expressions": {
            "$id": "8",
            "Literal": "5"
          }
        }
      ],
      "propertyStorageProviders": {}
    },
    {
      "$id": "9",
      "activityId": "4e346ab0-bcb0-4d5f-b175-0a5739f53e85",
      "type": "WriteLine",
      "displayName": "Write Line",
      "persistWorkflow": false,
      "loadWorkflowContext": false,
      "saveWorkflowContext": false,
      "properties": [
        {
          "$id": "10",
          "name": "Text",
          "syntax": "JavaScript",
          "expressions": {
            "$id": "11",
            "JavaScript": "(input)"
          }
        }
      ],
      "propertyStorageProviders": {}
    },
    {
      "$id": "12",
      "activityId": "439b8305-22a7-4d87-9af6-6fe9c17879af",
      "type": "WriteLine",
      "displayName": "Write Line",
      "persistWorkflow": false,
      "loadWorkflowContext": false,
      "saveWorkflowContext": false,
      "properties": [
        {
          "$id": "13",
          "name": "Text",
          "expressions": {
            "$id": "14",
            "Literal": "SUCCESS"
          }
        }
      ],
      "propertyStorageProviders": {}
    },
    {
      "$id": "15",
      "activityId": "7b1a127b-7da6-4006-af17-754dcd64878c",
      "type": "ForEach",
      "displayName": "For Each",
      "persistWorkflow": false,
      "loadWorkflowContext": false,
      "saveWorkflowContext": false,
      "properties": [
        {
          "$id": "16",
          "name": "Items",
          "syntax": "JavaScript",
          "expressions": {
            "$id": "17",
            "Literal": "(input)",
            "JavaScript": "activities.TestDataSource1.Output()"
          }
        }
      ],
      "propertyStorageProviders": {}
    }
  ],
  "connections": [
    {
      "$id": "18",
      "sourceActivityId": "32e64fb2-94ad-40a0-9f4e-2d6f1df771d9",
      "targetActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c",
      "outcome": "Done"
    },
    {
      "$id": "19",
      "sourceActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c",
      "targetActivityId": "4e346ab0-bcb0-4d5f-b175-0a5739f53e85",
      "outcome": "Iterate"
    },
    {
      "$id": "20",
      "sourceActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c",
      "targetActivityId": "439b8305-22a7-4d87-9af6-6fe9c17879af",
      "outcome": "Done"
    }
  ],
  "id": "91e42f8754a949b6aa5e64b1f2f92c96"
}

I will close this issue as solved, but feel free to follow-up with any questions or concerns.

[Oraeya]

I upgraded all Elsa packages to 2.3.0 but it still throws the same exception. Here is the exported Workflow JSON: { "$id": "1", "definitionId": "371ae20403c34965be434a5584216ad5", "versionId": "060cc3b9ad5d469ba7997dbba772ae53", "name": "loop_test_data", "displayName": "Loop test data", "version": 10, "variables": { "$id": "2", "data": {} }, "customAttributes": { "$id": "3", "data": {} }, "isSingleton": false, "persistenceBehavior": "WorkflowBurst", "deleteCompletedInstances": false, "isPublished": true, "isLatest": true, "activities": [ { "$id": "4", "activityId": "e8c51f8c-1118-4a07-9db0-10dfd70e4ee5", "type": "HttpEndpoint", "displayName": "HTTP Endpoint", "persistWorkflow": false, "loadWorkflowContext": false, "saveWorkflowContext": false, "properties": [ { "$id": "5", "name": "Path", "expressions": { "$id": "6", "Literal": "/loop-test" } }, { "$id": "7", "name": "Methods", "expressions": { "$id": "8", "Json": "[\"GET\"]" } }, { "$id": "9", "name": "ReadContent", "expressions": { "$id": "10" } }, { "$id": "11", "name": "TargetType", "expressions": { "$id": "12" } } ], "propertyStorageProviders": {} }, { "$id": "13", "activityId": "32e64fb2-94ad-40a0-9f4e-2d6f1df771d9", "type": "TestDataSource", "displayName": "Test", "persistWorkflow": false, "loadWorkflowContext": false, "saveWorkflowContext": false, "properties": [ { "$id": "14", "name": "EntryAmount", "expressions": { "$id": "15", "Literal": "50" } }, { "$id": "16", "name": "Columns", "expressions": { "$id": "17", "Literal": "5" } } ], "propertyStorageProviders": {} }, { "$id": "18", "activityId": "4e346ab0-bcb0-4d5f-b175-0a5739f53e85", "type": "WriteLine", "displayName": "Write Line", "persistWorkflow": false, "loadWorkflowContext": false, "saveWorkflowContext": false, "properties": [ { "$id": "19", "name": "Text", "syntax": "JavaScript", "expressions": { "$id": "20", "JavaScript": "(input)" } } ], "propertyStorageProviders": {} }, { "$id": "21", "activityId": "439b8305-22a7-4d87-9af6-6fe9c17879af", "type": "WriteLine", "displayName": "Write Line", "persistWorkflow": false, "loadWorkflowContext": false, "saveWorkflowContext": false, "properties": [ { "$id": "22", "name": "Text", "expressions": { "$id": "23", "Literal": "SUCCESS" } } ], "propertyStorageProviders": {} }, { "$id": "24", "activityId": "7b1a127b-7da6-4006-af17-754dcd64878c", "type": "ForEach", "displayName": "For Each", "persistWorkflow": false, "loadWorkflowContext": false, "saveWorkflowContext": false, "properties": [ { "$id": "25", "name": "Items", "syntax": "JavaScript", "expressions": { "$id": "26", "Literal": "(input)", "JavaScript": "(input)" } } ], "propertyStorageProviders": {} } ], "connections": [ { "$id": "27", "sourceActivityId": "e8c51f8c-1118-4a07-9db0-10dfd70e4ee5", "targetActivityId": "32e64fb2-94ad-40a0-9f4e-2d6f1df771d9", "outcome": "Done" }, { "$id": "28", "sourceActivityId": "32e64fb2-94ad-40a0-9f4e-2d6f1df771d9", "targetActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c", "outcome": "Done" }, { "$id": "29", "sourceActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c", "targetActivityId": "4e346ab0-bcb0-4d5f-b175-0a5739f53e85", "outcome": "Iterate" }, { "$id": "30", "sourceActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c", "targetActivityId": "439b8305-22a7-4d87-9af6-6fe9c17879af", "outcome": "Done" }, { "$id": "31", "sourceActivityId": "4e346ab0-bcb0-4d5f-b175-0a5739f53e85", "targetActivityId": "7b1a127b-7da6-4006-af17-754dcd64878c", "outcome": "Done" } ], "id": "060cc3b9ad5d469ba7997dbba772ae53" }

And the code for my Activity:

using System;
using System.Collections.Generic;
using Elsa;
using Elsa.ActivityResults;
using Elsa.Attributes;
using Elsa.Services;
using Elsa.Services.Models;
using ElsaQuickstarts.Server.DashboardAndServer.Exceptions;

namespace ElsaQuickstarts.Server.DashboardAndServer.Activities.DataSources
{
    [Activity(
        Category = "Data Source",
        DisplayName = "Test",
        Description = "Fetch dummy data.",
        Outcomes = new[] {OutcomeNames.Done}
    )]
    public class TestDataSource : Activity
    {
        [ActivityInput(Hint = "Number of entries")]
        public int EntryAmount { get; set; }

        [ActivityInput(Hint = "Number of columns")]
        public int Columns { get; set; }

        protected override IActivityExecutionResult OnExecute(ActivityExecutionContext context)
        {
            try
            {
                var result = new List<Dictionary<string, object>>();
                for (int i = 0; i < EntryAmount; i++)
                {
                    var entry = new Dictionary<string, object>();
                    for (int j = 0; j < Columns; j++)
                    {
                        entry.Add($"key{j + i * 10}", $"value{j + i * 10}");
                    }

                    result.Add(entry);
                }

                context.Output = result;
                return Done();
            }
            catch (Exception e)
            {
                throw new ActivityException("Creating Test data failed!", e);
            }
        }
    }
}

And my custom Exception:

using System;
using Elsa.Services.Models;

namespace ElsaQuickstarts.Server.DashboardAndServer.Exceptions
{
    public class ActivityException : Exception
    {
        public ActivityException() : base()
        {
        }

        public ActivityException(string message)
            : base(message)
        {
        }

        public ActivityException(string message, Exception inner)
            : base(message, inner)
        {
        }
    }
}

@sfmskywalker I hope you can reproduce the error with this 😃