Model, Props, FormModel, and EventPayload

Stability

Classifications for this surface are recorded in STABILITY.md.

Status: Accepted · Shipped

Hedron exposes purpose-specific model bases backed by Pydantic.

from hedron import Field, FormModel, Model, Props

class User(Model):
    id: int
    name: str

class UserCardProps(Props):
    user: User
    compact: bool = False

class CreateUser(FormModel):
    name: str = Field(min_length=1, label="Name")

Roles

Type	Role
Model	Portable domain data used by UI contracts
Props	Component construction input; never automatically exposed as HTTP input
FormModel	Client-submitted form or action input with field presentation metadata
EventPayload	Typed custom-event data crossing a browser/server boundary

from hedron import Field
from hedron_core import EventPayload


class ItemSelected(EventPayload):
    item_id: str = Field(min_length=1)

EventPayload is for structured browser→server (or server→browser event) payloads—not for form posts (FormModel) or component construction (Props).

Supported field shapes

Primitives, enums, literals, optionals, lists, string-keyed mappings, nested Hedron models, dates, SafeUrl, and component-node types where declared. Extra fields are forbidden by default. Secret and TrustedHtml follow security types. Presentation metadata (label, widgets) is owned by Field.

Errors

Situation	Behavior
Unsupported / contradictory Field options	Fail at class definition (HED-MODEL-*)
Arbitrary objects / callbacks as props	Fail at class definition
Invalid submitted payload	Pydantic/ValidationError in your handler

See also

• Field · Forms and actions
• Component