Summary

• Make ServerSentEvent generic — ServerSentEvent[Data] now validates that data is an instance of Data and emits a contentSchema for that type in the OpenAPI spec
• Bare ServerSentEvent (no type parameter) continues to accept any value including None, preserving full backward compatibility
• Add get_sse_data_type() helper used by the routing layer to detect parameterized ServerSentEvent[Data] annotations and extract Data for schema generation
• Add docs_src/server_sent_events/tutorial006_py310.py example and corresponding test
• Add documentation section "Typed ServerSentEvent" to the SSE tutorial

Motivation

Before this change, yielding ServerSentEvent objects from an SSE endpoint meant no data validation and no type information in the generated OpenAPI schema. Callers had to rely on documentation or convention to know what shape the data field would carry.

With ServerSentEvent[Item]:

@app.get("/items/stream", response_class=EventSourceResponse)
async def stream_items() -> AsyncIterable[ServerSentEvent[Item]]:
    for i, item in enumerate(items):
        yield ServerSentEvent[Item](data=item, event="item_update", id=str(i + 1))

• Pydantic validates that every event's data really is an Item (or raises ValidationError at construction time)
• The generated OpenAPI schema includes a contentSchema referencing Item, so clients and SDK generators know the exact payload shape

How it works

Pydantic's generic BaseModel creates a concrete subclass (not a _GenericAlias) when parameterized, so get_origen() returns None. The routing layer calls get_sse_data_type() which inspects __pydantic_generic_metadata__["args"] to extract Data. The routing logic then branches:

• ServerSentEvent[Data] → use Data as stream_item_type (feeds contentSchema)
• Bare ServerSentEvent → skip (no contentSchema, same as before)
• Any other type → use as-is (existing JSONL / plain-model path)

model_config = ConfigDict(validate_default=True) ensures that omitting data on a parameterized event raises a ValidationError rather than silently storing None.

Example output

"text/event-stream": {
  "itemSchema": {
    "type": "object",
    "properties": {
      "data": {
        "type": "string",
        "contentMediaType": "application/json",
        "contentSchema": { "$ref": "#/components/schemas/Item" }
      },
      "event": { "type": "string" },
      "id":    { "type": "string" },
      "retry": { "type": "integer", "minimum": 0 }
    },
    "required": ["data"]
  }
}

Checklist

• New tests cover the generic construction, validation, streaming, and OpenAPI schema
• Tutorial example (tutorial006_py310.py) and tutorial test added
• Backward compatibility: bare ServerSentEvent behaves identically to before
• ruff check and ruff format pass with no changes
• All 46 SSE tests pass