SPOT : UserDataStreamEventsResponse does not deserialize correctly, instance is always None

[mobias17]

Description

The UserDataStreamEventsResponse model fails to parse user data stream events into their concrete event types (BalanceUpdate, ExecutionReport, OutboundAccountPosition, EventStreamTerminated, etc.). All input results in None and the event data is completely lost.

Expected Behavior

When validating a user data stream event, the model should:

1. Parse the event dictionary into the appropriate concrete event type based on the "e" field
2. Return a strongly-typed instance (e.g., BalanceUpdate, ExecutionReport)
3. Preserve all event data fields

Example:

from binance_sdk_spot.websocket_api.models import UserDataStreamEventsResponse

event = {
    "e": "balanceUpdate",
    "E": 1573200697110,
    "a": "BTC",
    "d": "100.00000000",
    "T": 1573200697068
}

result = UserDataStreamEventsResponse.model_validate(event)
# Expected: result is a BalanceUpdate instance with all fields accessible
# Expected: result.a == "BTC"
# Expected: result.d == "100.00000000"
# Expected: result.E == 1573200697110
# Expected: result.e == "balanceUpdate"
# Expected: result.T == 1573200697068

Actual Behavior

The parsing always fails and returns None, losing all event data:

result = UserDataStreamEventsResponse.model_validate(event)
# Actual: result.actual_instance is None
# Actual: All event data is lost
# Actual: Cannot access event fields

Possible Root Cause

The model uses Pydantic's discriminated union pattern but fails to properly discriminate between event types. Issues include:

1. Schema Validation Failure: The discriminator field or schema mapping is not correctly configured
2. Type Resolution Failure: The model cannot resolve which concrete event type to instantiate
3. Silent Failure: Instead of raising validation errors, it silently returns None

This is similar to the SymbolFilters discriminated union issue that was previously identified, where filter type discrimination failed.

Impact

• Complete Data Loss: All user data stream events are lost when using this model
• No Balance Updates: Balance changes from outboundAccountPosition events cannot be processed
• No Order Updates: Order status changes from executionReport events cannot be tracked
• No Stream Monitoring: Stream termination events cannot be detected

Related Issues

• Similar to SPOT : SymbolFilters does not deserialize correctly, instance is always None #476 discriminated union parsing issue

References

Affected Version: >=2.1.0
Related or same as #405

[alplabin]

Hey @mobias17, Thank you for pointing out this issue and opening PRs. An update has been included in binance-sdk-spot latest version v7.0.0. Please give it a try, and feel free to share any feedback if you encounter issues.

[mobias17]

Hey @alplabin Thank you for the new versions. Good step in right direction. Still failing in v7.0.0. Explained a bit deeper in the PR #492.

[mobias17]

@alplabin
As mentioned in closing comment of PR, resolved.

However, one tiny remaining note:

binance-connector-python/clients/spot/src/binance_sdk_spot/websocket_api/models/user_data_stream_events_response.py

Lines 121 to 142 in 5725647

	if isinstance(parsed, dict) and "filterType" in parsed:
	filter_type_map = {
	"outboundAccountPosition": OutboundAccountPosition,
	"balanceUpdate": BalanceUpdate,
	"executionReport": ExecutionReport,
	"listStatus": ListStatus,
	"eventStreamTerminated": EventStreamTerminated,
	"externalLockUpdate": ExternalLockUpdate,
	}
	validator_mapping = {
	"OutboundAccountPosition": "oneof_schema_1_validator",
	"BalanceUpdate": "oneof_schema_2_validator",
	"ExecutionReport": "oneof_schema_3_validator",
	"ListStatus": "oneof_schema_4_validator",
	"EventStreamTerminated": "oneof_schema_5_validator",
	"ExternalLockUpdate": "oneof_schema_6_validator",
	}
	ft = parsed.get("filterType")
	target_cls = filter_type_map.get(ft)

an Event never has a key filterType. Seems to be taken from symbolFilers. Correct IMHO would be "e", event_type_map, et.

The parsing still works due to the old code, but the code behind if target_cls is not None: to deserialize directly into the proper schema seems never called.