Refering to your previous problem, you can use IndexMany for indexing the data. Now as per your question in comment, you can specify the id which elastic search will use. see the below example.
ElasticType(IdProperty = "<fieldName>")]
public class ClassName
{
if you dont want to specify any Id to elastic search, create a dummy field dummyId(nullable) and put it in "IdProperty". Elastic search will auto assign the value to it if it null.
Edit : From 2.3 onwards, Its
[ElasticsearchType(IdProperty = "<fieldName>")]