### Author:  [@shadyabhi](https://discuss.elastic.co/u/shadyabhi)
#### Post date: [November 20, 2016, 5:18am UTC](https://discuss.elastic.co/t/is-searching-by--id-faster-in-parent-child-relationship/66633/1 "2016-11-20T05:18:08Z")
I'm trying to model one-to-many relationships in Elasticsearch with ability to fetch parents and children without involving any searches.
**Question 1:** I thought that the way I can achieve this is by using `_id` wherever possible. Can someone confirm if fetching a document by doing `GET` request to `/index/type/1` faster than doing a term query on a field that's not `_id`?
Below is an example of 1 parent and its 2 children.
Parent (type: parent):-
```
{
"_id": "deterministic_id_1",
"app": "awesome-app-1",
"server": "awesome-server-1"
}
```
Children (type: children):-
```
{
"config": "awesome-config-1"
"_parent": "deterministic_id_1"
}
{
"config": "awesome-config-2"
"_parent": "deterministic_id_1"
}
```
I have deterministic \_id field so that I can fetch parent documents without searching. That already works, simply do a `GET` request for `/index/type/`.
I know that Elasticsearch maintains a mapping of all parent-\>child relationships internally. Now, how do I fetch all children for a parent without searching? Is there a way? Best I could come up with is:-
```
POST /index/children/_search
{
"query": {
"has_parent": {
"type": "parent",
"query": {
"ids": {
"type": "config_parent",
"_id": "deterministic_id_1"
}
}
}
}
}
```
**Question 2:** Does Is this the fastest way I can fetch all children for the parent with `_id` as `deterministic_id_1`? Does this query hit all shards?
I want two things from my data:-
1. Get access to all parents using my deterministic\_id\_1. (already done)
2. Get access to all children using the parent's document id without involving any searching. (pending)
---
### Author:  [@shadyabhi](https://discuss.elastic.co/u/shadyabhi)
#### Post date: [November 23, 2016, 3:18pm UTC](https://discuss.elastic.co/t/is-searching-by--id-faster-in-parent-child-relationship/66633/2 "2016-11-23T15:18:05Z")
Anyone?
---
### Author:  [@jpountz](https://discuss.elastic.co/u/jpountz)
#### Post date: [November 25, 2016, 3:15pm UTC](https://discuss.elastic.co/t/is-searching-by--id-faster-in-parent-child-relationship/66633/3 "2016-11-25T15:15:36Z")
> [@shadyabhi](#):
>
> Can someone confirm if fetching a document by doing GET request to /index/type/1 faster than doing a term query on a field that's not \_id?
It should perform a bit better but I would not expect it to be a game changer.
> [@shadyabhi](#):
>
> Question 2: Does Is this the fastest way I can fetch all children for the parent with \_id as deterministic\_id\_1? Does this query hit all shards?
I think you should be able to do something like this:
```auto
POST /index/children/_search?routing=deterministic_id_1
{
"query": {
"term": {
"_parent": "deterministic_id_1"
}
}
}
```
---
### Author:  [@shadyabhi](https://discuss.elastic.co/u/shadyabhi)
#### Post date: [November 25, 2016, 3:31pm UTC](https://discuss.elastic.co/t/is-searching-by--id-faster-in-parent-child-relationship/66633/4 "2016-11-25T15:31:37Z")
Hi @jpountz,
Thanks for the reply. I somehow missed query as one of the options.
I see that we're using a routing key. Can I safely assume that this is the fastest way to search all children for a parent?
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [December 23, 2016, 3:31pm UTC](https://discuss.elastic.co/t/is-searching-by--id-faster-in-parent-child-relationship/66633/5 "2016-12-23T15:31:39Z")
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