---
description: 'Learn what entities are in Medusa. There are entities defined in the Medusa backend, and developers can create custom entities.'
---

import DocCardList from '@theme/DocCardList';
import Icons from '@theme/Icon';
import LearningPath from '@site/src/components/LearningPath';

# Entities

In this document, you'll learn what Entities are in Medusa.

## What are Entities

Entities in medusa represent tables in the database as classes. An example of this would be the `Order` entity which represents the `order` table in the database. Entities provide a uniform way of defining and interacting with data retrieved from the database.

Aside from the entities in the Medusa core package, you can also create custom entities to use in your Medusa backend. Custom entities are TypeScript or JavaScript files located in the `src/models` directory of your Medusa backend. You then transpile these entities to be used during the backend's runtime using the `build` command, which moves them to the `dist/models` directory.

Entities are based on [Typeorm’s Entities](https://typeorm.io/entities) and use Typeorm decorators. Each entity also require a [repository](./repositories.md) to be created. A repository provides basic methods to access and manipulate the entity's data.

<LearningPath pathName="entity-and-api" />

---

## Base Entities

All entities must extend either the `BaseEntity` or `SoftDeletableEntity` classes. The `BaseEntity` class holds common columns including the `id`, `created_at`, and `updated_at` columns.

The `SoftDeletableEntity` class extends the `BaseEntity` class and adds another column `deleted_at`. If an entity can be soft deleted, meaning that a row in it can appear to the user as deleted but still be available in the database, it should extend `SoftDeletableEntity`.

---

## metadata Attribute

Most entities in Medusa have a `metadata` attribute. This attribute is an object that can be used to store custom data related to that entity. In the database, this attribute is stored as a [JSON Binary (JSONB)](https://www.postgresql.org/docs/current/datatype-json.html#JSON-CONTAINMENT) column. On retrieval, the attribute is parsed into an object.

Some example use cases for the `metadata` attribute include:

- Store an external ID of an entity related to a third-party integration.
- Store product customization such as personalization options.

### Add and Update Metadata

You can add or update metadata entities either through the REST APIs or through create and update methods in the entity's respective [service](../services/overview.mdx).

In the [admin REST APIs](https://docs.medusajs.com/api/admin), you'll find that in create or update requests of some entities you can also set the `metadata`.

In services, there are typically `create` or `update` methods that allow you to set or update the metadata.

If you want to add a property to the `metadata` object or update a property in the `metadata` object, you can pass the `metadata` object with the properties you want to add or update in it. For example:

```json
{
  // other data
  "metadata": {
    "is_b2b": true
  }
}
```

If you want to remove a property from the `metadata` object, you can pass the `metadata` object with the property you want to delete. The property should have an empty string value. For example:

```json
{
  // other data
  "metadata": {
    "is_b2b": "" // this deletes the `is_b2b` property from `metadata`
  }
}
```

---

## Custom Development

Developers can create custom entities in the Medusa backend, a plugin, or in a module, then ensure it reflects in the database using a migration.

<DocCardList colSize={4} items={[
  {
    type: 'link',
    href: '/development/entities/create',
    label: 'Create an Entity',
    customProps: {
      icon: Icons['academic-cap-solid'],
      description: 'Learn how to create an entity in Medusa.'
    }
  },
  {
    type: 'link',
    href: '/development/entities/repositories',
    label: 'Create a Repository',
    customProps: {
      icon: Icons['academic-cap-solid'],
      description: 'Learn how to use a repository in Medusa.'
    }
  },
  {
    type: 'link',
    href: '/development/entities/migrations/create',
    label: 'Create a Migration',
    customProps: {
      icon: Icons['academic-cap-solid'],
      description: 'Learn how to create migrations in Medusa.'
    }
  },
]} />

<DocCardList colSize={6} items={[
  {
    type: 'link',
    href: '/development/entities/extend-entity',
    label: 'Extend an Entity',
    customProps: {
      icon: Icons['academic-cap-solid'],
      description: 'Learn how to extend a core Medusa entity.'
    }
  },
  {
    type: 'link',
    href: '/development/entities/extend-repository',
    label: 'Extend a Repository',
    customProps: {
      icon: Icons['academic-cap-solid'],
      description: 'Learn how to extend a core Medusa repository.'
    }
  },
]} />
