---
title: Uniqueness Constraints
description: How Twenty enforces data uniqueness during import.
---
import { VimeoEmbed } from '/snippets/vimeo-embed.mdx';

## Overview

Twenty enforces uniqueness on certain fields to prevent duplicate records and ensure data integrity. Understanding these constraints is essential for successful imports.

## Default Unique Fields

| Object | Unique Fields |
|--------|---------------|
| **People** | `id`, `email` |
| **Companies** | `id`, `domain` |
| **Custom objects** | `id` only (by default) |

<Note>The `id` field is Twenty's internal identifier, auto-generated for each record. It uses UUID format (e.g., `c776ee49-f608-4a77-8cc8-6fe96ae1e43f`).</Note>

## Custom Unique Fields

You can define additional unique fields under **Settings → Data Model**:

1. Go to **Settings → Data Model**
2. Select the object
3. Click on a field
4. Enable **Unique** in field settings

### Use Cases for Custom Unique Fields
- **External IDs**: Store IDs from other systems (Salesforce ID, HubSpot ID)
- **Business identifiers**: Employee numbers, customer codes
- **Alternative contact info**: LinkedIn profile, phone number

<Note>The field name `id` is reserved for Twenty's internal ID. Use a different name like `externalId` or `legacyId` for external identifiers.</Note>

## Import Behavior

### Creating New Records
If a unique field value doesn't exist, a new record is created.

### Updating Existing Records
If a unique field value matches an existing record, that record is **updated** with the new data.
<Warning>To **update existing records**, it is recommended to **only match one unique field**.</Warning>

### Soft-Deleted Records

<Warning>
**Deleted records count toward uniqueness.**

Soft-deleted records (visible under Command Menu → See deleted records) are included in uniqueness checks. If you import a record with the same unique value as a deleted record, the deleted record will be **restored** with the new data.
</Warning>

## Duplicate Detection During Import

During the validation phase:
- Duplicates within your file are highlighted in yellow
- You can edit or remove duplicate rows from the UI before starting the import

<VimeoEmbed videoId="1145246326" title="Video demonstration" />

## Best Practices

1. **Remove duplicates** from your file before importing
2. **Check for existing records** in Twenty before importing
3. **Use external IDs** when migrating from other systems
4. **Include unique fields** if you want to update existing records