In the previous type of query, has_child, we wanted to get records of the parent_type query based on a query that we executed against the child type. The has_parent query is useful for exactly the opposite purpose, that is, when we want to get all child type of records based on a query executed against the parent_type. Let's learn about this through an example.

We want to get all the features of a specific product that has the product id = c0003. We can use a has_parent query as follows:

GET amazon_products_with_features/_search
{
  "query": {
    "has_parent": {
      "parent_type": "product",                                  1
      "query": {                                                 2
        "ids": {
          "values": ["c0001"]
        }
      }
    }
  }
}

Please note the following points, marked with the numbers in the query:

1. Under the has_parent query, we need to specify the parent_type against which the query needs to be executed to get the children (features).
2. The query element can be any Elasticsearch query that will be run against the parent_type. Here we want features of a very specific product and we already know the Elasticsearch ID field (_id) of the product. This is why we use the ids query with just one value in the array: c0001.

The result is all the features of that product:

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 3,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_index" : "amazon_products_with_features",
        "_type" : "doc",
        "_id" : "c0001_screen_size",
        "_score" : 1.0,
        "_routing" : "c0001",
        "_source" : {
          "product_or_feature" : {
            "name" : "feature",
            "parent" : "c0001"
          },
          "feature_key" : "screen_size",
          "parent_id" : "c0001",
          "feature_value" : "14 inches",
          "feature" : "Screen Size"
        }
      },
      {
        "_index" : "amazon_products_with_features",
        "_type" : "doc",
        "_id" : "c0001_processor_series",
        "_score" : 1.0,
        "_routing" : "c0001",
        "_source" : {
          "product_or_feature" : {
            "name" : "feature",
            "parent" : "c0001"
          },
          "feature_key" : "processor_series",
          "parent_id" : "c0001",
          "feature_value" : "Core i5",
          "feature" : "Processor Series"
        }
      },
      {
        "_index" : "amazon_products_with_features",
        "_type" : "doc",
        "_id" : "c0001_clock_speed",
        "_score" : 1.0,
        "_routing" : "c0001",
        "_source" : {
          "product_or_feature" : {
            "name" : "feature",
            "parent" : "c0001"
          },
          "feature_key" : "clock_speed",
          "parent_id" : "c0001",
          "feature_value" : "2.30 GHz",
          "feature" : "Clock Speed"
        }
      }
    ]
  }
}