Elasticsearch Parent ID Query - Syntax, Example, and Tips

The Parent ID Query in Elasticsearch is used to find child documents that belong to a specific parent document. This query type is particularly useful when working with parent-child relationships in Elasticsearch using the join field type.

Syntax

The basic syntax for a Parent ID Query is as follows:

{
  "parent_id": {
    "type": "child_type",
    "id": "parent_id"
  }
}

For more details, refer to the official Elasticsearch documentation on Parent ID Query.

Example Query

Here's an example of a Parent ID Query:

GET /my-index/_search
{
  "query": {
    "parent_id": {
      "type": "answer",
      "id": "1"
    }
  }
}

This query will return all "answer" documents that have a parent document with ID "1".

Common Issues

1. Incorrect join field configuration: Ensure that the join field is properly configured in your mapping.
2. Missing parent document: The parent document must exist for the query to return results.
3. Wrong type: Make sure you're using the correct child type in the query.

Best Practices

1. Use Parent ID Query in combination with other queries for more complex searches.
2. Consider using the has_parent or has_child queries for more flexible parent-child relationship queries.
3. Be aware of the performance implications when dealing with large numbers of child documents.

Frequently Asked Questions

Q: How does Parent ID Query differ from Has Parent Query?
A: Parent ID Query finds child documents based on a specific parent ID, while Has Parent Query finds child documents whose parent matches a query.

Q: Can I use Parent ID Query with nested documents?
A: No, Parent ID Query is specifically for parent-child relationships using the join field type, not for nested documents.

Q: How do I index documents for use with Parent ID Query?
A: You need to use the join field type in your mapping and specify the parent-child relationship when indexing documents.

Q: Is there a limit to the number of child documents a parent can have?
A: There's no hard limit, but having too many child documents can impact performance. It's recommended to keep the number of children per parent reasonable.

Q: Can I use Parent ID Query in a bool query?
A: Yes, you can combine Parent ID Query with other query types in a bool query for more complex search scenarios.