Mongo '_id' field not being added in ElasticSearch

The issue is that Elasticsearch does not index or store the id field by default:

_id

Each document indexed is associated with an id and a type. The _id field can be used to index just the id, and possible also store it. By default it is not indexed and not stored (thus, not created).

The _id field can be enabled to be indexed, and possibly stored, using the appropriate mapping attributes:

{    "tweet" : {        "_id" : {            "index" : "not_analyzed",            "store" : true        }    }}

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-id-field.html

The issue will be how to pass the "store": true parameters into the createMapping function of mongoosastic. You may need to play around a bit with the createMapping function, modify the code on your own or try to create the Elasticsearch mapping by hand prior to indexing any data.

There is no build-in way to do it with mongoosastic.

I always use map function and spread syntax(...) to join _id with all other fields:

let results = results.map(r => { return { '_id': r._id, ...r._source} } )

Another option is to to use hydration, but it will be much slower as it will do additional query against MongoDB.