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Clarify nested fields #2585

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62 changes: 62 additions & 0 deletions learn/inner_workings/datatypes.mdx
Original file line number Diff line number Diff line change
Expand Up @@ -200,6 +200,68 @@ After flattening, it would look like this:

Once all objects inside a document have been flattened, Meilisearch will continue processing it as described in the previous sections. For example, arrays will be flattened, and numeric and boolean values will be turned into strings.

### Nested document querying and subdocuments

Meilisearch has no concept of subdocuments and cannot perform nested document querying. In the previous example, the relationship between an appointment's date and doctor is lost when flattening the `appointments` array:

```json
"appointments.date": [
"2022-01-01",
"2019-01-01"
],
"appointments.doctor": [
"Jester Lavorre",
"Dorian Storm"
],
```

This may lead to unexpected behavior during search. The following dataset shows two patients and their respective appointments:

```json
[
{
"id": 0,
"patient_name": "Imogen Temult",
"appointments": [
{
"date": "2022-01-01",
"doctor": "Jester Lavorre"
}
]
},
{
"id": 1,
"patient_name": "Caleb Widowgast",
"appointments": [
{
"date": "2022-01-01",
"doctor": "Dorian Storm"
},
{
"date": "2023-01-01",
"doctor": "Jester Lavorre"
}
]
}
]
```

The following query returns patients `0` and `1`:

```sh
curl \
-X POST 'http://localhost:7700/indexes/movie_ratings/search' \
-H 'Content-Type: application/json' \
--data-binary '{
"q": "",
"filter": "(appointments.date CONTAINS 2022-01-01 AND appointments.doctor CONTAINS 'Jester Lavorre')"
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}'
```

Meilisearch is unable to only return patients who had an appointment with `Jester Lavorre` in `2022-01-01`. Instead, it returns patients who had an appointment with `Jester Lavorre`, and patients who had an appointment in `2022-01-01`.
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## Possible tokenization issues

Even if it behaves exactly as expected, the tokenization process may lead to counterintuitive results in some cases, such as:
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1 change: 1 addition & 0 deletions learn/what_is_meilisearch/comparison_to_alternatives.mdx
Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,7 @@ Can't find a client you'd like us to support? [Submit your idea or vote for it](
|---|:---:|:----:|:---:|:---:|
| Schemaless | ✅ | ✅ | ✅ | ✅ |
| Nested field support | ✅ | ✅ | ✅ | ✅ |
| Nested document querying | ❌ | ❌ | ❌ | ✅ |
| Automatic document ID detection | ✅ | ❌ | ❌ | ❌ |
| Native document formats | `JSON`, `NDJSON`, `CSV` | `JSON` | `JSON`, `NDJSON` | `JSON`, `NDJSON`, `CSV` |

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