How to assign a new field a certain type and value?

Elastic Stack Logstash
2

Perhaps surprisingly, mutate { add_field => { somefield => 1 } } doesn't actually add an integer field:

$ cat test.config
input { stdin { } }
output { stdout { codec => rubydebug } }
filter {
  mutate {
    add_field => { "somefield" => 1 }
  }
}
$ echo 'foo' | /opt/logstash/bin/logstash -f test.config
Logstash startup completed
{
       "message" => "foo",
      "@version" => "1",
    "@timestamp" => "2015-11-09T19:45:06.364Z",
          "host" => "hallonet",
     "somefield" => "1"
}
Logstash shutdown completed

Use a second mutate filter to convert the field.