> Markdown version of [Fields & Binding](https://vaadin.com/docs/v24/building-apps/forms-data/add-form/fields-and-binding). Section index: [llms.txt](https://vaadin.com/docs/v24/building-apps/llms.txt)

# Fields and Binding

Forms are used to display and edit data in UI components called **fields**. This data comes from a **Form Data Object** (FDO), which is structured to align with the fields in the form. Each form field typically maps to a corresponding property in the FDO.

FDOs are often fetched from and submitted to an [application service](https://vaadin.com/docs/v24/building-apps/forms-data/add-form/loading-and-saving.md) for processing, such as validation and persistence. Architecturally, **an FDO belongs to the application layer**, not the presentation layer.

> **Important: Entities as Form Data Objects**
>
> In simple cases — such as CRUD views and administration screens — the form model and the domain model may be the same. In those cases, **you can use your entities as FDOs**. However, doing so **couples your domain logic to the UI**. This can lead to maintainability issues, especially if UI requirements evolve independently of business logic. When that happens, it’s better to introduce a dedicated FDO and handle data conversion in the application service.

Data is exchanged between the form and the FDO through **data binding**. Typically, each field is bound to a specific property of the FDO. The binding mechanism keeps the form and the FDO in sync.

> **Tip: Part of a Series**
>
> This is part 1 of the **Add a Form** series.

Both Flow and Hilla have many different field components and offer built-in support for data binding:

- [Fields and Binding in Flow](https://vaadin.com/docs/v24/building-apps/forms-data/add-form/fields-and-binding/flow.md)

- [Fields and Binding in Hilla](https://vaadin.com/docs/v24/building-apps/forms-data/add-form/fields-and-binding/hilla.md)