[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › Relation

Bidirectional relations with O(1) lookup in both directions.

## Functions

| Function                                                                                               | Description                                                                                            |
| ------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------ |
| [createRefCountedRelation](https://evolu.dev/docs/api-reference/common/Relation/functions/createRefCountedRelation) | Creates a [RefCountedRelation](https://evolu.dev/docs/api-reference/common/Relation/interfaces/RefCountedRelation). |
| [createRelation](https://evolu.dev/docs/api-reference/common/Relation/functions/createRelation)                     | Creates a [Relation](https://evolu.dev/docs/api-reference/common/Relation/interfaces/Relation).                     |

## Interfaces

| Interface                                                                                         | Description                                                                                     |
| ------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------- |
| [CreateRelationOptions](https://evolu.dev/docs/api-reference/common/Relation/interfaces/CreateRelationOptions) | Options for [createRelation](https://evolu.dev/docs/api-reference/common/Relation/functions/createRelation). |
| [RefCountedRelation](https://evolu.dev/docs/api-reference/common/Relation/interfaces/RefCountedRelation)       | Bidirectional relation with a positive retain count for every active pair.                      |
| [Relation](https://evolu.dev/docs/api-reference/common/Relation/interfaces/Relation)                           | Bidirectional relation between two types.                                                       |