ElasticSearch: Parent/Child: Find children based on parent properties

gistfile1.sh

#!/bin/bash

# Reset the index.
curl -X DELETE "localhost:9200/test/?pretty=true"
curl -X PUT "localhost:9200/test/?pretty=true"

# Create the parent mapping.
echo
curl -X PUT "localhost:9200/test/user/_mapping?pretty=true" -d '{
  "user": {
    "properties": {
      "firstname":  { "type": "string" },
      "lastname":   { "type": "string" }
    }
  }
}'

# Create the child mapping.
echo
curl -X PUT "localhost:9200/test/message/_mapping?pretty=true" -d '{
  "message": {
    "_parent": { "type": "user" },

    "properties": {
      "content":  { "type": "string" }
    }
  }
}'

# Index some parents.
echo
curl -X POST "localhost:9200/test/user/1" -d '{
  "firstname": "Nick",
  "lastname": "Hoffman"
}'
echo
curl -X PUT "localhost:9200/test/user/2" -d '{
  "firstname": "Nick",
  "lastname": "Smith"
}'

# Index some parents
echo
curl -X PUT "localhost:9200/test/message/3?parent=1" -d '{
  "content": "A message by Nick."
}'
echo
curl -X PUT "localhost:9200/test/message/4?parent=2" -d '{
  "content": "A message by John."
}'

# Search for messages by people whose firstname is "Nick".
#
# *** This returns no results. ***
#
echo
curl -X GET "localhost:9200/test/message/_search?pretty=1" -d '{
  fields: ["_parent", "content"],

  query:  {
    term: { "_parent.firstname": "Nick" }
  }
}'