In Elasticsearch, you can define a nested type that allows you to store arrays of objects and query them as separate entities. However, Elasticsearch does not directly support recursive nested types, which means you cannot have a nested object containing another nested object of the same type in a recursive manner.

To illustrate this limitation, consider the following example of a blog post with comments:

json
{ "post_id": 1, "title": "Elasticsearch Recursive Nested Type", "comments": [ { "comment_id": 101, "text": "This is a comment.", "replies": [ { "comment_id": 201, "text": "This is a nested reply to comment 101.", "replies": [ { "comment_id": 301, "text": "This is a nested reply to comment 201.", "replies": [ ... // This structure cannot be recursively nested in Elasticsearch ] } ] } ] } ] }

As you can see, the comments field contains nested objects with a replies field, which also contains nested objects with their replies field, and so on. This recursive nesting is not supported in Elasticsearch.

To handle such scenarios, you typically flatten the nested structure by denormalizing the data. Instead of having a recursive nested structure, you can store comments and replies as separate documents in the index and use a field to denote the parent-child relationship, like the parent_comment_id. This way, you can query and retrieve comments and replies in a non-recursive manner.

Here's an example of denormalized data for the blog post with comments:

json
{ "post_id": 1, "title": "Elasticsearch Recursive Nested Type" } { "comment_id": 101, "text": "This is a comment.", "post_id": 1, "parent_comment_id": null } { "comment_id": 201, "text": "This is a nested reply to comment 101.", "post_id": 1, "parent_comment_id": 101 } { "comment_id": 301, "text": "This is a nested reply to comment 201.", "post_id": 1, "parent_comment_id": 201 }

With this flattened structure, you can use Elasticsearch's regular queries to retrieve comments and replies based on the post_id and parent_comment_id fields, and you can achieve the same functionality without the need for recursive nested types.

Keep in mind that the denormalized approach may lead to some data duplication, but it allows you to work around the limitation of recursive nested types in Elasticsearch.

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