Store mixed data-type in ElasticSearch

I am using logstash to manage my application logs. I want to store some context data along with the log entries. These context data doesn't have to be indexed. But it can have can have different structure/data type depending on the application context. For example, the context can be in any of the following formats

String

{
    error: "This is a sample error message"
}

Array

{
    error: [
        "This is an error message", 
        "This is another message", 
        "This is the final message"
    ]
}

Or it could be an object

{
    error: {
        user_name: "Username cannot be empty",
        user_email: "Email address is already in use",
        user_password: "Passwords do not match"
    }
}

Is it possible to have such a field in ElasticSearch? The field does not have to be indexed, it just needs to be stored.

I don't think it's possible to do exactly what you're asking. You can get the first two examples for free, though, since any field can be a list:

curl -XDELETE "http://localhost:9200/test_index"

curl -XPUT "http://localhost:9200/test_index" -d'
{
    "mappings": {
        "doc": {
            "properties": {
                "error": {
                    "type": "string",
                    "index": "not_analyzed"
                }
            }
        }
    }
}'

curl -XPUT "http://localhost:9200/test_index/doc/1" -d'
{
    "error": "This is a sample error message"
}'

curl -XPUT "http://localhost:9200/test_index/doc/2" -d'
{
    "error": [
        "This is an error message", 
        "This is another message", 
        "This is the final message"
    ]
}'

curl -XPOST "http://localhost:9200/test_index/_search"
...
{
   "took": 2,
   "timed_out": false,
   "_shards": {
      "total": 5,
      "successful": 5,
      "failed": 0
   },
   "hits": {
      "total": 2,
      "max_score": 1,
      "hits": [
         {
            "_index": "test_index",
            "_type": "doc",
            "_id": "1",
            "_score": 1,
            "_source": {
               "error": "This is a sample error message"
            }
         },
         {
            "_index": "test_index",
            "_type": "doc",
            "_id": "2",
            "_score": 1,
            "_source": {
               "error": [
                  "This is an error message",
                  "This is another message",
                  "This is the final message"
               ]
            }
         }
      ]
   }
}

Alternatively, you could set up the mapping according to your third example, and then just use the fields needed for each document (complicating your application code, presumably):

curl -XDELETE "http://localhost:9200/test_index"

curl -XPUT "http://localhost:9200/test_index"

curl -XPUT "http://localhost:9200/test_index/doc/3" -d'
{
    "error": {
        "user_name": "Username cannot be empty",
        "user_email": "Email address is already in use",
        "user_password": "Passwords do not match"
    }
}'

curl -XGET "http://localhost:9200/test_index/_mapping"
...
{
   "test_index": {
      "mappings": {
         "doc": {
            "properties": {
               "error": {
                  "properties": {
                     "user_email": {
                        "type": "string"
                     },
                     "user_name": {
                        "type": "string"
                     },
                     "user_password": {
                        "type": "string"
                     }
                  }
               }
            }
         }
      }
   }
}

So basically the direct answer to your question is "No", unless I'm missing something (which is quite possible).

Here is the code I used:

http://sense.qbox.io/gist/18476aa6c2ad2fa554b472d09934559c884bec33