# Validation

{% hint style="success" %}
This is the official documentation of the `forestadmin-agent-django` and `forestadmin-agent-flask` Python agents.
{% endhint %}

![A field failing validation](https://2921382565-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F2HgnlEINLUAEQC1KgN48%2Fuploads%2Fgit-blob-8668bc8ffc7b3c737c80351447aa58c6eed2f303%2Ffield-validation-error.png?alt=media)

* Columns of type `VARCHAR(15)` will automatically carry a `less than 15 chars` validator.
* Non-nullable columns will automatically carry a `Present` validator.

However, you may want to enforce stricter restrictions than the ones which are implemented in your data source.

### Adding validation rules

The list of operators (`Present`, `LongerThan`, ...) which can be used when adding validators is the same as the [filter operators](https://docs.forestadmin.com/developer-guide-agents-python/data-sources/getting-started/queries/filters#operators).

```python
collection.add_field_validation(
    "firstName", "present"
).add_field_validation(
    "firstName", "longer_than", 2
).add_field_validation(
    "firstName", "shorter_than", 30
).add_field_validation(
    "firstName", "match", r"^[a-z]+$"
)
```


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