how to set mapping for _id in elasticsearch -

i creating new index 'collegedatabase' type 'studenttable' , id 123,1234,12345 etc; when trying record id 1234 returning record of 123 only. have tried set mapping '_id' field follows:

{    "studenttable" : {       "_id" : {         "index" : "not_analyzed"        }    } } 

still showing same result. can please me this. using this(it node.js)

client.search({         index: 'collegedatabase',         type: 'studenttable',         id: req.body.sid     },function(err,resp){       ............. });