# Basic ruby field adding not working
**URL:** https://discuss.elastic.co/t/basic-ruby-field-adding-not-working/223853
**Category:** Logstash
**Created:** [March 17, 2020, 6:45am UTC](https://discuss.elastic.co/t/basic-ruby-field-adding-not-working/223853 "2020-03-17T06:45:32Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@imrago](https://discuss.elastic.co/u/imrago)
#### Post date: [March 17, 2020, 6:45am UTC](https://discuss.elastic.co/t/basic-ruby-field-adding-not-working/223853/1 "2020-03-17T06:45:32Z")
Hi,
attempted to add a new field with ruby and not even a simple adding is working, what could be wrong?
> input {
> beats {
> port =\> 5044
> }
> }
>
> filter {
> ruby {
> code =\> "event['testfield'] = 'test'"
> }
> }
>
> output {
> elasticsearch {
> hosts =\> ["[http://localhost:9200](http://localhost:9200)"]
> index =\> "test-%{+yyyy.MM.dd}"
> }
> }
The error:
[2020-03-16T21:44:36,713][ERROR][logstash.filters.ruby][main] Ruby exception occurred: undefined method `=' for #LogStash::Event:0x115fa2a0
---
### Author:  [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [March 17, 2020, 12:44pm UTC](https://discuss.elastic.co/t/basic-ruby-field-adding-not-working/223853/2 "2020-03-17T12:44:01Z")
Elastic removed the ability to refer to an event as a hash years ago. Use the [event.set API call](https://www.elastic.co/guide/en/logstash/current/event-api.html).
---
### Author:  [@imrago](https://discuss.elastic.co/u/imrago)
#### Post date: [March 17, 2020, 2:22pm UTC](https://discuss.elastic.co/t/basic-ruby-field-adding-not-working/223853/3 "2020-03-17T14:22:07Z")
Thank you, that was the problem, used an outdated documentation.
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [April 14, 2020, 2:22pm UTC](https://discuss.elastic.co/t/basic-ruby-field-adding-not-working/223853/4 "2020-04-14T14:22:10Z")
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