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I have a .NET 8 service which uses Hangfire library for async jobs. I have configured Hangfire with PostgreSQL database.

I need to check the state of a running job frequently for which I am using the PostgreSqlConnection.GetStateData method of the Hangfire.PostgreSql library in the following way:

private StateData GetJobState(string jobId)
{
    using (var connection = JobStorage.Current.GetConnection())
    {
        var state = connection.GetStateData(jobId);
        return state;
    }
}

I am getting the following exception intermittently in this method call:

Unable to find a default constructor to use for type Hangfire.PostgreSql.PostgreSqlMonitoringApi+SafeDictionary`2[System.String,System.String].
Path 'State', line 1, position 136.

StackTrace:
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateNewDictionary(JsonReader reader, JsonDictionaryContract contract, Boolean& createdFromNonDefaultCreator)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
at Hangfire.Common.SerializationHelper.Deserialize(String value, Type type, SerializationOption option)
--- End of stack trace from previous location ---
at Hangfire.Common.SerializationHelper.Deserialize(String value, Type type, SerializationOption option)
at Hangfire.Common.SerializationHelper.Deserialize[T](String value, SerializationOption option)
at Hangfire.Common.SerializationHelper.Deserialize[T](String value)
at Hangfire.PostgreSql.PostgreSqlConnection.GetStateData(String jobId)

What could be the reason for this exception? I don't understand why it is trying to deserialize the state data dictionary into type Hangfire.PostgreSql.PostgreSqlMonitoringApi+SafeDictionary2[System.String,System.String].

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1 Answer 1

Reset to default
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Why This Error Occurs

1. Serialization Conflict: The job state data was serialized as a regular dictionary but is being deserialized into Hangfires internal SafeDictionary type
2. Intermittent Nature: This typically happens when:
Reading state data written by a different Hangfire version
During certain job state transitions
When the serialization format doesn't match the deserialization expectations

Recommended Solutions

1. Upgrade Hangfire.PostgreSql (Best Solution)

dotnet add package Hangfire.PostgreSql --version latest

Many serialization issues have been fixed in newer versions.

2. Use the Monitoring API Instead The monitoring API is more stable for reading job states:

    private StateData GetJobState(string jobId)    {
        var monitoringApi = JobStorage.Current.GetMonitoringApi();
        var jobDetails = monitoringApi.JobDetails(jobId);
        return jobDetails?.History?.LastOrDefault(); // or filter by state
    }
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