twenty/packages/twenty-docs/developers/extend/apps/data/overview.mdx

---
title: Overview
description: Shape the data your app adds to a workspace — objects, fields, and relations.
icon: "database"
---

A Twenty app's **data layer** is the data your app *adds* to a workspace — the new record types it declares, the columns it adds to existing objects, and how those records connect to each other.

```text
┌──────────────────────────────────────────────────┐
│ Object — a record type, e.g. PostCard            │
│    ├─ Field     (name, type, label)              │
│    ├─ Field                                      │
│    └─ Relation  (link to another object)         │
└──────────────────────────────────────────────────┘
            │
            ├── lives in your app, OR
            │
            ▼
┌──────────────────────────────────────────────────┐
│ Standard / other apps' objects                   │
│    └─ Field added by your app via defineField    │
└──────────────────────────────────────────────────┘
```

## In this section

<CardGroup cols={2}>
  <Card title="Objects" icon="table" href="/developers/extend/apps/data/objects">
    `defineObject` — declare new record types with their own fields.
  </Card>
  <Card title="Extending Objects" icon="wand-magic-sparkles" href="/developers/extend/apps/data/extending-objects">
    `defineField` — add fields to standard or other apps' objects.
  </Card>
  <Card title="Relations" icon="diagram-project" href="/developers/extend/apps/data/relations">
    Bidirectional `MANY_TO_ONE` / `ONE_TO_MANY` connections between objects.
  </Card>
</CardGroup>

## Entities at a glance

| Entity | Purpose | Defined with |
|--------|---------|--------------|
| **Object** | A new custom record type (e.g. PostCard, Invoice) with its own fields | `defineObject()` |
| **Field** | A column on an object. Standalone fields can extend objects you didn't create (e.g. add `loyaltyTier` to Company) | `defineField()` |
| **Relation** | A bidirectional link between two objects — both sides declared as fields | `defineField()` with `FieldType.RELATION` |
| **Index** | A database index to speed up a recurring query on one of your objects | `defineIndex()` |

The SDK detects these via AST analysis at build time, so file organization is up to you — the convention is `src/objects/`, `src/fields/`, and `src/indexes/`. Stable `universalIdentifier` UUIDs tie everything together across deploys.

## Indexes (optional)

Apps can ship indexes alongside their objects to keep recurring queries fast. The most common case is a status or foreign-key column that you read frequently.

```ts src/indexes/post-card-status.index.ts
import { defineIndex } from 'twenty-sdk/define';

import {
  POST_CARD_UNIVERSAL_IDENTIFIER,
  STATUS_FIELD_UNIVERSAL_IDENTIFIER,
} from '../objects/post-card.object';

export default defineIndex({
  universalIdentifier: 'b6e9d2a1-5a4c-46ca-9d52-42c8f02d1ff0',
  objectUniversalIdentifier: POST_CARD_UNIVERSAL_IDENTIFIER,
  fields: [
    {
      universalIdentifier: 'b6e9d2a1-5a4c-46ca-9d52-42c8f02d1ff1',
      fieldUniversalIdentifier: STATUS_FIELD_UNIVERSAL_IDENTIFIER,
    },
  ],
});
```

### Unique indexes

`defineIndex` accepts `isUnique: true` for both single- and multi-column uniqueness. This is the recommended primitive — `defineField({ isUnique: true })` is deprecated and will be removed in a future release.

```ts
defineIndex({
  universalIdentifier: '…',
  objectUniversalIdentifier: PERSON_UNIVERSAL_IDENTIFIER,
  isUnique: true,
  fields: [{ universalIdentifier: '…', fieldUniversalIdentifier: EMAIL_FIELD_UNIVERSAL_IDENTIFIER }],
});
```

### Other constraints

- Partial `WHERE` clauses stay under admin control — apps can't declare them.
- Each object is capped at 10 custom indexes (the framework's own indexes don't count).

Order the `fields` array the way Postgres should use it — leftmost column first, like a phone book. Indexes are not free: every write to the table updates them. Add one only when you have a query that needs it.

<Note>
Looking for **Application Config** or **Roles & Permissions**? Those describe the app itself rather than the data it adds — they live under [Config](/developers/extend/apps/config/overview). Looking for **Connections** (Linear, GitHub, Slack OAuth)? Those exist to be called *from* logic functions and live under [Logic](/developers/extend/apps/logic/connections).
</Note>