elsa-workflows/elsa-core · error · Exception

Failed to deserialize

Error message

Failed to deserialize {stringValue} to {underlyingTargetType}

What it means

ObjectConverter.ConvertTo wraps JsonSerializer.Deserialize failures in a generic Exception with a message showing the string and target type. It is thrown when a JSON-looking string ('{' or '[' prefixed) cannot be deserialized to the underlying target type.

Solutions

1. Validate the string is well-formed JSON of the expected shape before conversion
2. Fix the stored value so it matches the target type schema
3. Catch Exception around ConvertTo and log stringValue for diagnosis, then supply a fallback

Example fix

// before
var options = ObjectConverter.ConvertTo<MyOptions>(rawString);
// after
MyOptions options;
try { options = ObjectConverter.ConvertTo<MyOptions>(rawString); }
catch (Exception e) { logger.LogError(e, "Bad value: {V}", rawString); options = new MyOptions(); }

if (s.TrimStart().StartsWith('{') || s.TrimStart().StartsWith('['))
    using (var doc = JsonDocument.Parse(s)) { /* shape check */ }

try { result = ObjectConverter.ConvertTo<T>(s); } catch (Exception e) { logger.LogError(e, "Convert failed for: {Value}", s); result = default; }

When it happens

Trigger: Calling ConvertTo<T> (or via activity property conversion) with a string value that starts with '{' or '[' whose content is not valid JSON or does not match the target type shape.

Common situations: Workflow input/property values stored as JSON strings in definitions; malformed JSON saved by designers or hand-edited definitions; target type changed between versions.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

• Cannot deserialize to .
• Invalid variable test values.
• The binding to activity type
• Expected number or string.
• Cannot convert to bool

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/3dd739f813bd14e5. Report an issue: GitHub.

Appendix: source

Thrown at src/clients/Elsa.Api.Client/Extensions/ObjectConverter.cs:83

        }

        if (value is JsonNode jsonNode)
            return jsonNode.Deserialize(targetType, options);

        if (underlyingSourceType == typeof(string) && !underlyingTargetType.IsPrimitive && underlyingTargetType != typeof(object))
        {
            var stringValue = (string)value;

            try
            {
                var firstChar = stringValue.TrimStart().FirstOrDefault();

                if (firstChar is '{' or '[')
                    return JsonSerializer.Deserialize(stringValue, underlyingTargetType, options);
            }
            catch (Exception)
            {
                throw new Exception($"Failed to deserialize {stringValue} to {underlyingTargetType}");
            }
        }

        if (targetType == typeof(object))
            return value;

        if (underlyingTargetType.IsInstanceOfType(value))
            return value;

        if (underlyingSourceType == underlyingTargetType)
            return value;

        if (IsDateType(underlyingSourceType) && IsDateType(underlyingTargetType))
            return ConvertAnyDateType(value, underlyingTargetType);

        if (typeof(IDictionary<string, object>).IsAssignableFrom(underlyingSourceType) && underlyingTargetType.IsClass)
        {
            if (typeof(ExpandoObject) == underlyingTargetType)

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