Form definition: Actions

Forms can contain buttons which invoke actions on the server side. Each action must have a unique name (fields also have names, but unlike action names, they are automatically inferred). An action name can only contain letters, digits and _ (no spaces or other characters which would form an invalid JSON object key).

In its simplest form, an action can modify the object that is backing the form, and needs to return an ActionResult:

case class Person(name: String)

val personForm = form[Person](f => List(
  f.action("duplicateName")(p => ActionResult(p.copy(name = s"${} ${}"))
    .label("Duplicate name")

Actions can result not only in modified objects, but also return some custom data (JSON) to the client. You can either return both an object and custom data using ActionResult(obj, Some(jvalue)), or only custom data using ActionResult.custom(jvalue). Depending on the variant, when the JSON is generated, the custom data will be placed next to the form data, or will replace the whole generated JSON.

To implement some operations on subforms, such as removing a subform element, or moving the elements around, it is necessary to have access to the parent object. This is possible by using ``parentAction``s. The subform is in such case parametrised by the action (so it can be reused in different contexts), which is provided in the parent form:

case class Address(street: String)
case class Person(name: String, addresses: List[Address]) {
  def removeAddress(a: Address) = this.copy(addresses = this.addresses diff List(a))

def addressForm(removeAction: Address => ActionResult[Address]) = form[Address](f => List(

val personForm = form[Person](f => List(
  f.subform(_.addresses, addressForm(
    f.parentAction((person, index, address) => ActionResult(person.removeAddress(address)))))

To enable sending form content automatically when an action is invoked, see the section on frontend refreshes).

Before-action validation


Before an action is run, the form can be validated. By default, no validations are run before an action is invoked. You can customize that behavior using the .validate...() methods on an action field.

You can validate either the entire form, the current subform or run no validations at all. For example, when implementing a “save form” action, you will most probably want to validate all fields in the form:

val personForm = form[Person](f => List(
  f.action("save")(p => ActionResult(persist(p))).label("Save").validateAll()