# Difference of Parent to Child Documents and a Nested Document **URL:** \ **Category:** Elasticsearch\ **Created:** [August 23, 2012, 10:18pm UTC](https://discuss.elastic.co/t/difference-of-parent-to-child-documents-and-a-nested-document/8839 "2012-08-23T22:18:14Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![phill](https://avatars.discourse-cdn.com/v4/letter/p/779978/32.png) [@phill](https://discuss.elastic.co/u/phill)\ **Post date:** [August 23, 2012, 10:18pm UTC](https://discuss.elastic.co/t/difference-of-parent-to-child-documents-and-a-nested-document/8839/1 "2012-08-23T22:18:14Z")
I can understand the different between a multi-value field that contains many objects and a Nested Document. The main problem solvable by nested objects is "cross object" matching, see [http://www.elasticsearch.org/guide/reference/mapping/nested-type.html](http://www.elasticsearch.org/guide/reference/mapping/nested-type.html) But why would I use a nested object vs. a parent object & one or more child objects? For query that includes the child, I can use a has\_child query (or filter) [http://www.elasticsearch.org/guide/reference/query-dsl/has-child-query.html](http://www.elasticsearch.org/guide/reference/query-dsl/has-child-query.html) For a query that includes a nested document I can use a nested\_ query [http://www.elasticsearch.org/guide/reference/query-dsl/nested-query.html](http://www.elasticsearch.org/guide/reference/query-dsl/nested-query.html) Both result in 1 document for the parent and 1 for each child. Is one of the primary differences between nested object and a child/parent is that A nested type is defined/changed/deleted by indexing a new parent while a child document can have a different lifecycle than its parent? My application of parent/child would definitely be a case where the children come along at different times after the parent is created. -Paul -- ---
**Author:** ![Clinton\_Gormley](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Clinton\_Gormley](https://discuss.elastic.co/u/Clinton_Gormley)\ **Post date:** [August 24, 2012, 6:36am UTC](https://discuss.elastic.co/t/difference-of-parent-to-child-documents-and-a-nested-document/8839/2 "2012-08-24T06:36:39Z")
On Thu, 2012-08-23 at 15:19 -0700, P. Hill wrote: > I can understand the different between a multi-value field that contains > many objects and a Nested Document. > The main problem solvable by nested objects is "cross object" matching, see > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/mapping/nested-type.html) > > But why would I use a nested object vs. a parent object & one or more > child objects? > > For query that includes the child, I can use a has\_child query (or filter) > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/query-dsl/has-child-query.html) > For a query that includes a nested document I can use a nested\_ query > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/query-dsl/nested-query.html) > Both result in 1 document for the parent and 1 for each child. > > Is one of the primary differences between nested object and a > child/parent is that > A nested type is defined/changed/deleted by indexing a new parent > while a child document can have a different lifecycle than its parent? Correct > My application of parent/child would definitely be a case where the > children come along at different times after the parent is created. It's also a question of the number of children. I'd guess (not sure) that nested docs probably perform better than parent-child docs, but if you could have thousands of children, you will probably do better with parent-child. clint > -Paul -- ---
**Author:** ![mvg](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/mvg/32/98890_2.png) [@mvg](https://discuss.elastic.co/u/mvg)\ **Post date:** [August 24, 2012, 8:20am UTC](https://discuss.elastic.co/t/difference-of-parent-to-child-documents-and-a-nested-document/8839/3 "2012-08-24T08:20:19Z")
Hi Paul, With nested objects you basically need to know your parent child relation upfront. You can't add a nested object after the main document is added. This isn't the case with parent child objects. So based on your requirements I would suggest that parent child type object is the way to go. Martijn On 24 August 2012 08:36, Clinton Gormley [clint@traveljury.com](mailto:clint@traveljury.com) wrote: > On Thu, 2012-08-23 at 15:19 -0700, P. Hill wrote: > > > I can understand the different between a multi-value field that contains > > many objects and a Nested Document. > > The main problem solvable by nested objects is "cross object" matching, see > > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/mapping/nested-type.html) > > > > But why would I use a nested object vs. a parent object & one or more > > child objects? > > > > For query that includes the child, I can use a has\_child query (or filter) > > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/query-dsl/has-child-query.html) > > For a query that includes a nested document I can use a nested\_ query > > [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/query-dsl/nested-query.html) > > Both result in 1 document for the parent and 1 for each child. > > > > Is one of the primary differences between nested object and a > > child/parent is that > > A nested type is defined/changed/deleted by indexing a new parent > > while a child document can have a different lifecycle than its parent? > > Correct > > > My application of parent/child would definitely be a case where the > > children come along at different times after the parent is created. > > It's also a question of the number of children. > > I'd guess (not sure) that nested docs probably perform better than > parent-child docs, but if you could have thousands of children, you will > probably do better with parent-child. > > clint > > > -Paul > > -- -- Met vriendelijke groet, Martijn van Groningen -- ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 3:15am UTC](https://discuss.elastic.co/t/difference-of-parent-to-child-documents-and-a-nested-document/8839/4 "2017-07-06T03:15:13Z")