Not able to create multiple nested type mapping for hierarchical json data

I have a json file which contains hierarchical structure. I want to create multiple nested type mapping for this data. When i do it and try to search a field it gives exception in search query.
Below is the example of json data that I have. I cannot post original data cos its forbidden.
{
"elementType" : {
"type" : "knowledge",
"entity" : [ { "media" : "book"
"subject" : [
{"name" : "maths" ,
"division" : [
{"name" : "linear Algebra"},
{"name" : "calculas"},
{"name" : "sets"}
]},
{"name" : "economics",
"division" : [
{"name" : "macro economics"},
{"name" : "micro economics"}
]}
{ "name" : "biology"}
]},
{ "media" , "DVD"},
{ "media", "usb"}

			               ]
			 }

}

i was able to create nested mapping for entity . I am not able to create nested mapping for subject

var mapping={
"mappings": {
"poc": {
"properties": {
elementType.entity": {
"type": "nested"
}
}
}
}
}

Need help to create nested mapping for elementType.entity.subject,
elementType.entity.subject.division. I have taken too many days looking and trying solutions but everything in vein. Please help. If you have any better suggestion feel free to add it. Please note i cannot change my json hierarchy.

You don’t use the dot notation in the mappings- ‘elementType’ is declared as type nested then you have a ‘properties’ field at the same level to declare the fields it holds eg “entity”.
Before you do - are you sure you need the overhead of nested docs? If the objects only have one property (“name”) there’s no need for a nested doc. See this flowchart

This is the sample json that i have provided that i have provided. My actual json is very huge. this is just a simulation of the original 1. I will require Nested type cos i will query inner json arrays.. I am ready to live with the overhead. Regarding not to use. operator i wasnt able to follow u. can you post me some example from my json.
i want to nest elementType.entity & elementType.entity.subject & elementType.entity.subject.division. This are arrays. any help will be appreciated.
if I add entity as nested object and perform nested search on elementType.entity.media = knowledge it works fine . But if i try to add another nested object like elementType.entity.subject the same query used to find media throws exception "reason": [nested] nested object under path elementType.entity is not of nested type"

{
  "mappings": {
	"poc": {
	  "properties": {
		"elementType": {
		  "type": "nested",
		  "properties": {
			"entity": {
			  "type": "nested",
			  "properties": {
				"name": {
				  "type": "text"
				}
			  }
			}
		  }
		}
	  }
	}
  }
}