> ## Documentation Index
> Fetch the complete documentation index at: https://docs.twenty.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Uniqueness Constraints

> How Twenty enforces data uniqueness during import.

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## 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

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## 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