Presentation

A thin edge that maps the wire model to a command, calls one use case, and maps failures back out.

clean-architecturepresentation

Presentation is the incoming adapter. It turns an outside request into one use case call, then turns the result or the failure into the response that caller understands. A screen, an endpoint, and a job runner are all presentation when they are the thing that invokes the workflow.

What lives here

Artifact	Notes example	Why it is here
Entry point	`NotesEndpoint.save` or a submit handler	Receives the outside call
Wire model	`SaveNotePayload`	Fields and names the client speaks
Mapper	`toSaveNoteCommand`	Wire model to command, result to wire model
Failure mapper	`InvalidTitle` to the client's error	The caller does not import domain types

The entry point stays thin:

text

save(request):
  command = toSaveNoteCommand(request.payload)
  result = saveNote.execute(command)
  return toSaveNoteResponse(result)

Auth context that arrived with the request (who is calling) is read here and placed on the command. The policy that decides whether that person may save a note is a use case step, or a domain rule, depending on whether it is a workflow or an invariant. The entry point does not re-implement it.

The wire model

The payload is the third model at the boundary. It exists to be serialized. It is allowed to be awkward in ways the entity is not: optional fields, names that match a public API, ids omitted on create because the server assigns them.

text

SaveNotePayload
  title
  body

SaveNoteResponse
  id
  title
  body
  createdAt

The client sends no id and no createdAt. The response has both, because the use case created them. That difference is a reason the payload is not a Note. If the public API renames body to text, the mapper changes. Note does not.

Errors across a boundary

Failures mean different things, and presentation is where they become a response.

Failure	Raised by	What presentation does
`InvalidTitle`	Domain, while creating the note	A client error that names the field
Not found	Application, when a load returns nothing the workflow required	A client error for an unknown id
Store timeout, connection reset	Infrastructure	A server failure. The title was fine

Do not catch a store timeout inside the domain and rethrow it as InvalidTitle. Do not let the use case format an error string for a particular client. Map at the edge, once, so a second entry point can map the same failure differently.

Unexpected failures can stay unexpected. Presentation maps the ones it knows. A programming bug is not a domain failure and does not need a polite field error.

What stays outside

Constructing SqlNoteRepository or any concrete adapter
Business invariants (title is not blank)
Multi-step workflows
Query text

If the entry point grows past the map-call-map shape, the extra steps belong in the use case. The edge is replaceable: the same SaveNote serves an HTTP route, a generated RPC endpoint, or a test that calls execute directly.