Parent Child example

parent_child.txt

DELETE chat

PUT chat
{
  "settings": {
    "index": {
      "number_of_shards": "1",
      "number_of_replicas": "1"
    }
  },
  "mappings": {
    "doc": {
      "properties": {
        "user_comment_relation": {
          "type": "join",
          "relations": {
            "user": "comment"
          }
        }
      }
    }
  }
}

GET chat

PUT chat/doc/chat_01
{
  "user": "foo",
  "appid": "foos_app",
  "user_comment_relation": {
    "name": "user"
  }
}

PUT chat/doc/chat_02
{
  "user": "bar",
  "appid": "bars_app",
  "user_comment_relation": {
    "name": "user"
  }
}

PUT chat/doc/comment_01_01?routing=chat_01
{
  "text": "hello",
  "user_comment_relation": {
    "name": "comment",
    "parent": "chat_01"
  }
}

PUT chat/doc/comment_01_02?routing=chat_01
{
  "text": "world",
  "user_comment_relation": {
    "name": "comment",
    "parent": "chat_01"
  }
}

PUT chat/doc/comment_02_01?routing=chat_02
{
  "text": "world",
  "user_comment_relation": {
    "name": "comment",
    "parent": "chat_02"
  }
}


GET chat/_search
{
  "query": {
    "match": {
      "text": "world"
    }
  }
}

# The only case where the join field makes sense is if your data contains a one-to-many relationship where one entity significantly outnumbers the other entity

# https://www.elastic.co/guide/en/elasticsearch/reference/6.2/parent-join.html

# https://www.elastic.co/guide/en/elasticsearch/reference/6.2/search-request-inner-hits.html#parent-child-inner-hits

POST chat/_search
{
  "query": {
    "has_child": {
      "type": "comment",
      "query": {
        "match": {
          "text": "world"
        }
      },
      "inner_hits": {}    
    }
  }
}

POST chat/_search
{
  "query": {
    "bool": {
      "filter": {
        "term": {
          "appid.keyword": "foos_app"
        }
      }
    }
  }
}

POST chat/_search
{
  "query": {
    "bool": {
      "filter": {
        "term": {
          "appid.keyword": "foos_app"
        }
      },
      "must": {
        "has_child": {
         "type": "comment",
          "query": {
            "match": {
            "text": "world"
          }
        },
        "inner_hits": {}    
        }
      }
    }
  }
}