---
title: "Legacy xDB facet"
slug: "legacy-xdb-facet"
abstract: "Guide to how interaction IDs are mapped from Sitecore 8.x to 9 in xDB Data Migration Tool."
---
# Legacy xDB facet

<details>
<summary><h2>Format in Sitecore 8.x</h2></summary>

In Sitecore 8.x, each interaction has a unique identifier. This identifier is the document id, which is stored in a property named `_id`.

The following is an example of an interaction with the `_id` property:

```text
"_id" : NUUID("ac95ec0b-fba0-466b-8b51-a2f3e887e1d2"),
```

</details>

<details>
<summary><h2>Format in Sitecore 9</h2></summary>

When an interaction from Sitecore 8.x is migrated to Sitecore 9, xConnect generates a new id for the interaction. The interaction id from Sitecore 8.x is associated with the interaction through an interaction facet:

|     |     |
| --- | --- |
| Facet Name | `LegacyXdb` |
| Facet Type | `Sitecore.DataExchange.Tools.XdbDataMigration.Models.DataMigrationCollectionModel` |

</details>

<details>
<summary><h2>Mapping details</h2></summary>

|     |     |
| --- | --- |
| Mapping definition | MongoDB to xConnect Interaction Mappings > MongoDB Interaction to xConnect Interaction Legacy xDB Facet |

| Value to write to target object | Property on target object |
| --- | --- |
| `_id` from source object | `LegacyId` |

</details>