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# NSO Service Model form field reference

> How to create and configure Form Builder forms using NSO YANG service models, including constraint validation, field properties, and deleting fields.

## Guidelines

* To view device elements from a service model in Form Builder, specify where to find the YANG files. In NSO adapter version 4 and higher, configure the `yangdirs` property in the adapter.
* In older NSO adapter versions (pre-version 4), include your YANG schemas in the `load-path` of `ncs.conf`.
* For more information, see the NSO NETCONF adapter documentation.

## Create a form using an NSO YANG service model

#### Select a service

Select the appropriate service from the **Data Elements** dropdown list. The leafs defined in the model display automatically below the dropdown.

#### Assign fields

Drag and drop the fields onto the form. By default, each field label matches the leaf name from the service model. Click a field and type a new label to change it.

#### Assign lists

Assign the **Lists** defined in NSO to the form.

#### Group fields in containers

Click **Add Container** to group fields together. Toggle the direction icon (double arrow in the left corner) to arrange containers horizontally or vertically. Containers can be nested within other containers.

#### Name and save

Assign a name to the form and click **Save**.

![](/_fern-img/3a34a07680e9a966634e740c64a002105a4eeb58fc67605816d87da1fb6f0fd0.webp)

### Meta Data fields

In addition to leafs from an NSO YANG service model, you can assign Meta Data Fields to a form. The following field types are available:

* **Text Box** — Allows any characters.
* **Number Field** — Accepts only numerical values.
* **Checkbox** — A boolean field that can be checked or unchecked.
* **Dropdown** — Accepts one selected option from a dropdown list.

![](/_fern-img/60177567b85ca567be8359ffee26049b34d263f7e1deff52176dfdf95898d409.webp)

## Preview a form

Once a form is saved, click the **Form Preview** button (eye icon) in the title bar to preview the form.

![](file:docs/assets/images/platform/studio/05-previewForm\(1\).png)

All form fields are editable in Preview mode, including those configured as a leaf reference or enumeration in the YANG service model, just as they are when the form is used in a workflow.

![](/_fern-img/04796ca589bbc82b994f25c0daa9f3cff468d0b762a9fc33a1b30f0a3163afd5.webp)

## Enable or disable constraints

The **Validate Constraints** checkbox allows you to bypass the `must` statement validations defined in the YANG service models. The checkbox works at the form level — disabling it disables validations for the entire form. It does not disable other form validations.

### Examples

The example below shows a form with a leaf `description` that has a length constraint (3 to 8 characters) and a `must` statement (`leafWithMust`) that requires `description` to be exactly 5 characters.

![](/_fern-img/defff8ac69c8fedc866d8b10ae41b9267ca7a382f91ab651cedd555f93dff996.webp)

When `description` has only two characters, an error message displays for the leaf:

![](/_fern-img/389135aa9e01c20529ea42a5aff2e636b3670bd80873f5be6fe8acf4d5363837.webp)

Disabling **Validate Constraints** does not remove the length error for the field:

![](/_fern-img/bd91f24d49521041072b6e54c0ab62c2b553a34db67a37dd73d1ccfa4699d510.webp)

When `description` has three characters, the length validation passes — but `leafWithMust` now fails because it requires exactly 5 characters:

![](/_fern-img/7df9abd5cd15056b9d9789ff17fa86b1afca58dcb7acc3a544d0c129c419d5a3.webp)

When **Validate Constraints** is unchecked, the `must` statement validation is disabled and the form reports no errors:

![](/_fern-img/fedfae32ba0fec2b056e27abdb0f88d2777b4a91ce25361b4a176e3ff7ba3288.webp)

## Mandatory vs. required field constraint validation

Some fields are **mandatory** — they must contain a value and this cannot be overridden. Mandatory fields always display a red asterisk (\*) or the text "Required" next to the field label. **Constraints** can also restrict values based on the value of another field. If expected data is missing or incorrectly formatted, an error message displays.

### Examples

Mandatory constraint validation:

![](/_fern-img/a9e4419eba8f8124ee083af0ec27a99b910633ca7cb3223dfa08e9ab0f3728fc.webp)

For **required** field constraint validation, there is a dependency between the `key` and the `required` field element. When a nested table `key` is not entered, the form skips the table row:

![](/_fern-img/16061196e0bf8edfd4597d8617ce1d92e848e22f20d88091df649210417a6fd0.webp)

When the table `key` is missing, the form submits but the table row is ignored regardless of whether Field A or Field B was filled in:

![](/_fern-img/195503289f156b1cfb493128f230d26171984000e6d549fed87d59e831b4c0db.webp)

**Output (missing key):**

```json
{
  "name": [
    "test"
  ]
}
```

When the table key is present but required fields are empty, the form cannot be submitted:

![](/_fern-img/4eef10d4395bec5f6450ddae5980fce5de5645568ab279ffb7bd6fa3c6186913.webp)

A successful submission includes a valid table key and all required fields:

![](/_fern-img/3d688aaf725f741faa94dd12e7bc0871d3257337f703b797cee6cfb79a477532.webp)

**Output (successful):**

```json
{
  "name": [
    "testValCrit"
  ],
  "table": [
    [
      {
        "key": "1",
        "fieldA": "A",
        "fieldB": "B"
      }
    ]
  ]
}
```

### Resources

* [YANG Data Modeling — Keys in Lists (RFC 7950)](https://datatracker.ietf.org/doc/html/rfc7950#page-85)
* [MDN Constraint Validation](https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Constraint_validation)

## Edit form field properties

#### Open the Configure dialog

Hover over the field and click the **Configure Properties** icon in the top-right corner of the field. The **Configure** dialog opens.

![](/_fern-img/0f046f8aaaa9ea20b1b2adebe5d252a26458539d134bfd058ead58db88c38ef3.webp)![](/_fern-img/efdfc63816b23e80bc083154c3b9a1081e880d53ffe2a3670852619193abfa6f.webp)

| Property             | Description                                                                                                                                                                        |
| -------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Custom Label         | Adds a custom label above the field.                                                                                                                                               |
| Field Key            | An internal value that identifies the field in the workflow engine. Update this only for a Meta Data Field — do not modify it when the field is part of an NSO YANG service model. |
| Info / Tool Tip      | Adds a custom tooltip that displays when the cursor is placed over the field.                                                                                                      |
| Required             | When checked, the form cannot be submitted unless a value has been entered in the field.                                                                                           |
| Read-Only            | When checked, the field is visible but cannot be modified by users.                                                                                                                |
| Hide Field           | When checked, the field is hidden from users but remains available to the workflow engine.                                                                                         |
| Min Length           | The minimum number of characters a Text field must contain before it can be submitted.                                                                                             |
| Max Length           | The maximum number of characters a Text field may contain before it can be submitted.                                                                                              |
| Regex Patterns       | Does not apply to fields assigned an NSO leaf reference or enumeration.                                                                                                            |
| Custom Error Message | Adds a custom error message when user input is invalid. Requires that Field Type be defined.                                                                                       |

## Delete a form field

Click the trashcan icon on the field to remove it.

![](/_fern-img/23e5980d0d9a81c2de9b18df201ed00677250213cfe79b3997bb06d63ec4e0f5.webp)

> How to create and configure Form Builder forms using NSO YANG service models, including constraint validation, field properties, and deleting fields.