> ## Documentation Index
> Fetch the complete documentation index at: https://forest-chore-open-api.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Enrich your models

> ⚠️ This page is relevant only if you installed Forest directly on a database (SQL/Mongodb). If you installed in a Rails/Django/Laravel app, you manage your models like you normally would.

### Declaring a new model

Whenever you have a new table/collection in your database, you will have to create file to declare it. Here is a **template example** for a `companies` table:

### Declaring a new field in a model

Any new field must be added **manually** within the corresponding model of your `/models` folder.

### Managing nested documents in Mongoose

<Info>
  For a better user experience, flatten nested fields. In v2 see the [Flattener plugin](/product/process/advanced-concepts/plugins/overview).
</Info>

Lumber introspects your data structure recursively, so ***nested fields*** (object in object) are detected any level deep. Your **sub-documents** (array of nested fields) are detected as well.

<Warning>
  Conflicting data types will result in the generation of a [mixed](https://mongoosejs.com/docs/schematypes.html#mixed) type field.
</Warning>

The following model...

...will result in the following interface:

<img src="https://mintcdn.com/forest-chore-open-api/TmGmEqoffYUVv4Df/images/legacy/javascript-agents/nested-documents-field-customization-mongoose.png?fit=max&auto=format&n=TmGmEqoffYUVv4Df&q=85&s=387cfaaed35c87df0318aa65d28a7da0" alt="" width="1920" height="1001" data-path="images/legacy/javascript-agents/nested-documents-field-customization-mongoose.png" />

### Removing a model

By default **all** tables/collections in your database are analyzed by Lumber to generate your models. If you want to exclude some of them to prevent them from appearing in your Forest, check out [this how-to](/legacy/ruby-agent/how-tos/settings/include-exclude-models).

### Adding validation to your models

Validation allows you to keep control over your data's quality and integrity.

<Info>
  If your existing app already has validation conditions, you may - or may not - want to reproduce the same validation conditions in your admin backend's models.&#x20;

  If so, you'll have to do it **manually**, using the below examples.
</Info>

Depending on your database type, your models will have been generated in *Sequelize* (for SQL databases) or *Mongoose* (for Mongo databases).

###

### Adding a default value to your models

You can choose to add a default value for some fields in your models. As a result, the corresponding fields will be prefilled with their default value in the creation form:

### Adding a hook

Hooks are a powerful mechanism which allow you to automatically **trigger an event** at specific moments in your records lifecycle.&#x20;

In our case, let's pretend we want to update a `update_count` field every time a record is updated: