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Add user documentation about unique index creation #2856

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Jun 19, 2023
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Add user documentation about unique index creation #2856

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Update user docs about unique index creation support
rumyantseva Jun 19, 2023
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26 changes: 22 additions & 4 deletions website/docs/indexes.md
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Expand Up @@ -45,22 +45,40 @@ If it's `-1`, it specifies a descending order direction for the index.
### Compound Indexes

For compound indexes, you can create an index key combining multiple fields together as a key.
Below is an example of a compound index that uses `price` and `category` fields from the `products` collection as the index key.
Below is an example of a compound index that uses `price` and `category` fields
from the `products` collection as the index key:

```js
db.products.createIndex({ price: 1, category: 1 })
```

:::note
### Unique Indexes

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You can create unique indexes to ensure that the indexed fields do not contain duplicate values.
To create a unique index, set the `unique` option as `true` when calling `createIndexes()` command.

Below is an example of a unique index for the `name` field from the `products` collection:

```js
db.products.createIndex({ name: 1 }, { unique: true })
```

Unique indexes can be compound.
Here is an example of a unique index consisting
of the `category` and `name` fields from the `products` collection:

```js
db.products.createIndex({ category: 1, name: 1 }, { unique: true })
```

### Index creation details
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@rumyantseva A separate section may be quite confusing since we have one on how to create indexes. Let's add this to the section above on how to create indexes.

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It can be a subsection there too or just as extra details after this sentence You can create single field indexes or compound indexes.

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"Index creation details" is a subsection of "How to create indexes", not a top-level section

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@Fashander Please send a new PR to improve that page if needed


- If the `createIndexes()` command is called for a non-existent collection, it will create the collection and its given indexes.
- If the `createIndexes()` command is called for a non-existent field, an index for the field is created without creating or adding the field to an existing collection.
- If you attempt to create an index with the same name and key as an existing index, the system will not create a duplicate index.
Instead, it will simply return the name and key of the existing index, since duplicate indexes would be redundant and inefficient.
- Meanwhile, any attempt to call `createIndexes()` command for an existing index using the same name and different key, _or_ different name but the same key will return an error.

:::

## How to list Indexes

To display a collection's index details, use the `listIndexes()` command.
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2 changes: 1 addition & 1 deletion website/docs/reference/supported-commands.md
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Expand Up @@ -584,7 +584,7 @@ Related [issue](https://github.com/FerretDB/FerretDB/issues/1917).
| | `indexes` | | ✅ | |
| | | `key` | ✅ | |
| | | `name` | ✅️ | |
| | | `unique` | ❌ | [Unimplemented](https://github.com/FerretDB/FerretDB/issues/2045) |
| | | `unique` | ✅ | |
| | | `partialFilterExpression` | ❌ | [Unimplemented](https://github.com/FerretDB/FerretDB/issues/2448) |
| | | `sparse` | ❌ | [Unimplemented](https://github.com/FerretDB/FerretDB/issues/2448) |
| | | `expireAfterSeconds` | ❌ | [Unimplemented](https://github.com/FerretDB/FerretDB/issues/2415) |
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