fix: JsonMapper / data.source.parse don't touch LEAN-inherited properties (v0.1.1)

v0.1.0 had a parse-time bug surfaced the moment a consumer actually
ran the bridge against the live API: FlashAlphaJsonMapper.PopulateProperties
(C#) iterates ALL public properties on the bar — including the inherited
BaseData.Symbol whose declared type is QuantConnect.Symbol, not string.
The JSON key "symbol":"SPY" snake-cased to "Symbol" and the deserializer
threw JsonException trying to convert "SPY" into a QC Symbol object. The
Python parse() loop hit the same hazard via setattr(bar, "Symbol", "SPY")
silently clobbering the QC Symbol instance with the raw ticker string.

Fix: only walk properties declared on the bar SUBCLASS (and any non-
QuantConnect ancestors). LEAN-owned surface (Symbol/Time/EndTime/Value/Price)
is set explicitly by FlashAlphaSource.Parse before this method runs.

CI tests passed previously only because they skipped when FLASHALPHA_API_KEY
was absent — no live data reached the parse path. Setting the secret on
the next CI run will exercise it for real.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: tdobrowolski1

CHANGELOG.md

@@ -8,6 +8,12 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/) and
 
 _No changes yet._
 
+## [0.1.1] — 2026-05-30
+
+### Fixed
+
+- **`FlashAlphaJsonMapper` (C#) and `data.source.parse` (Python) no longer overwrite inherited LEAN properties from the JSON.** Previously the snake-case auto-mapper would walk every public property on the bar — including inherited `BaseData.Symbol` / `PythonData.Symbol` — and try to set them from JSON keys like `"symbol":"SPY"`. In C# this threw `JsonException` ("could not convert to `QuantConnect.Symbol`") at the very first parse; in Python it silently clobbered the QC Symbol object with the raw ticker string. The mapper now walks only attributes declared on the bar subclass (and any non-`QuantConnect.*` ancestors), so LEAN-owned surface is left alone. Caught by running v0.1.0 as a real NuGet consumer — surfaces on the first `FlashAlphaSource.Parse` against the live API.
+
 ## [0.1.0] — 2026-05-30
 
 Initial public release. The bridge ships with full coverage of the FlashAlpha historical API surface as native QuantConnect LEAN custom-data bars, for both C# and Python.
@@ -26,5 +32,6 @@ Initial public release. The bridge ships with full coverage of the FlashAlpha hi
 - **Documentation corpus.** Repo-root `README.md` with side-by-side C# + Python examples, `docs/getting-started.md`, `docs/data-types.md` (per-bar field reference for all 17 endpoints), `docs/auth.md`, `docs/troubleshooting.md`, and five `docs/recipes/*.md` cookbooks.
 - **`llms.txt`** site map per [llmstxt.org](https://llmstxt.org/).
 
-[Unreleased]: https://github.com/FlashAlpha-lab/flashalpha-quantconnect/compare/v0.1.0...HEAD
+[Unreleased]: https://github.com/FlashAlpha-lab/flashalpha-quantconnect/compare/v0.1.1...HEAD
+[0.1.1]: https://github.com/FlashAlpha-lab/flashalpha-quantconnect/compare/v0.1.0...v0.1.1
 [0.1.0]: https://github.com/FlashAlpha-lab/flashalpha-quantconnect/releases/tag/v0.1.0

src/csharp/FlashAlpha.QuantConnect/Data/FlashAlphaJsonMapper.cs

@@ -28,9 +28,28 @@ internal static class FlashAlphaJsonMapper
     public static void PopulateProperties(object bar, JsonElement root)
     {
         if (root.ValueKind != JsonValueKind.Object) return;
+
+        // Walk only properties declared on the bar SUBCLASS — never inherited
+        // ones. BaseData ships an inherited Symbol/Time/Price/Value/EndTime
+        // surface; the JSON's "symbol" key would otherwise auto-route into
+        // BaseData.Symbol (typed QuantConnect.Symbol) and the deserializer
+        // would throw on the string value. FlashAlphaSource.Parse already
+        // sets Symbol/Time/EndTime explicitly before calling this method.
         var type = bar.GetType();
+        for (var t = type; t != null && t != typeof(object); t = t.BaseType)
+        {
+            // Stop walking once we hit anything from QuantConnect.* — that's
+            // LEAN's base hierarchy (BaseData, IBaseDataBar, ...). Subclass
+            // properties remain in play.
+            if (t.Namespace?.StartsWith("QuantConnect", StringComparison.Ordinal) == true) break;
+            PopulateFromType(bar, t, root);
+        }
+    }
 
-        foreach (var prop in type.GetProperties(BindingFlags.Public | BindingFlags.Instance))
+    private static void PopulateFromType(object bar, Type declaring, JsonElement root)
+    {
+        const BindingFlags flags = BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly;
+        foreach (var prop in declaring.GetProperties(flags))
         {
             if (!prop.CanWrite) continue;
             var jsonName = prop.GetCustomAttribute<JsonPropertyNameAttribute>()?.Name

src/csharp/FlashAlpha.QuantConnect/FlashAlpha.QuantConnect.csproj

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <PackageId>FlashAlpha.QuantConnect</PackageId>
     <RootNamespace>FlashAlpha.QuantConnect</RootNamespace>
-    <Version>0.1.0</Version>
+    <Version>0.1.1</Version>
     <Authors>FlashAlpha</Authors>
     <Company>FlashAlpha</Company>
     <Copyright>Copyright (c) 2026 FlashAlpha</Copyright>

src/python/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "flashalpha-quantconnect"
-version = "0.1.0"
+version = "0.1.1"
 description = "FlashAlpha options-flow and dealer-positioning data as QuantConnect LEAN custom-data bars. GEX, DEX, VEX, vol surface, 0DTE, VRP, max-pain."
 readme = "README.md"
 license = "MIT"

src/python/src/flashalpha_quantconnect/__init__.py

@@ -1,6 +1,6 @@
 """FlashAlpha options-flow data as QuantConnect LEAN custom-data bars."""
 
-__version__ = "0.1.0"
+__version__ = "0.1.1"
 
 from . import config
 from .data.exposure import (

src/python/src/flashalpha_quantconnect/data/source.py

@@ -84,9 +84,23 @@ def parse(bar_cls: Type, line: str, symbol: Any, date: datetime) -> Any:
     if not isinstance(obj, dict):
         return bar
 
+    # Collect attribute names declared on the bar SUBCLASS (and any non-LEAN
+    # ancestors). We deliberately stop walking at the LEAN base — its
+    # ``Symbol`` / ``Time`` / ``EndTime`` / ``Value`` / ``Price`` attributes
+    # are already populated above, and the JSON's ``symbol`` key would
+    # otherwise auto-route into ``BaseData.Symbol`` and clobber the QC
+    # Symbol object with the raw ticker string.
+    declared: set[str] = set()
+    for cls in bar_cls.__mro__:
+        mod = getattr(cls, "__module__", "") or ""
+        if mod.startswith("QuantConnect") or cls is object:
+            break
+        declared.update(vars(cls).keys())
+        declared.update(getattr(cls, "__annotations__", {}).keys())
+
     for snake, value in obj.items():
         prop = _to_pascal_case(snake)
-        if hasattr(bar, prop):
+        if prop in declared:
             setattr(bar, prop, value)
 
     # Honor explicit field-name aliases declared on the bar class.