Fix Flow initialization with Pydantic models having required fields

- Modified _create_initial_state() to accept kwargs parameter
- Pass kwargs when instantiating BaseModel classes
- Updated __init__() to pass kwargs to _create_initial_state()
- Added comprehensive tests covering various scenarios

Fixes #3744

Co-Authored-By: João <joao@crewai.com>

src/crewai/flow/flow.py

@@ -539,8 +539,8 @@ class Flow(Generic[T], metaclass=FlowMeta):
         self._persistence: FlowPersistence | None = persistence
         self._is_execution_resuming: bool = False
 
-        # Initialize state with initial values
+        # Initialize state with initial values and kwargs
-        self._state = self._create_initial_state()
+        self._state = self._create_initial_state(kwargs if kwargs else None)
         self.tracing = tracing
         if (
             is_tracing_enabled()
@@ -549,9 +549,6 @@ class Flow(Generic[T], metaclass=FlowMeta):
         ):
             trace_listener = TraceCollectionListener()
             trace_listener.setup_listeners(crewai_event_bus)
-        # Apply any additional kwargs
-        if kwargs:
-            self._initialize_state(kwargs)
 
         crewai_event_bus.emit(
             self,
@@ -577,9 +574,12 @@ class Flow(Generic[T], metaclass=FlowMeta):
                         method = method.__get__(self, self.__class__)
                     self._methods[method_name] = method
 
-    def _create_initial_state(self) -> T:
+    def _create_initial_state(self, kwargs: dict[str, Any] | None = None) -> T:
         """Create and initialize flow state with UUID and default values.
 
+        Args:
+            kwargs: Optional dictionary of initial state values
+
         Returns:
             New state instance with UUID and default values initialized
 
@@ -587,13 +587,16 @@ class Flow(Generic[T], metaclass=FlowMeta):
             ValueError: If structured state model lacks 'id' field
             TypeError: If state is neither BaseModel nor dictionary
         """
+        if kwargs is None:
+            kwargs = {}
+            
         # Handle case where initial_state is None but we have a type parameter
         if self.initial_state is None and hasattr(self, "_initial_state_t"):
             state_type = self._initial_state_t
             if isinstance(state_type, type):
                 if issubclass(state_type, FlowState):
-                    # Create instance without id, then set it
+                    # Create instance with kwargs
-                    instance = state_type()
+                    instance = state_type(**kwargs)
                     if not hasattr(instance, "id"):
                         instance.id = str(uuid4())
                     return cast(T, instance)
@@ -602,35 +605,42 @@ class Flow(Generic[T], metaclass=FlowMeta):
                     class StateWithId(state_type, FlowState):  # type: ignore
                         pass
 
-                    instance = StateWithId()
+                    instance = StateWithId(**kwargs)
                     if not hasattr(instance, "id"):
                         instance.id = str(uuid4())
                     return cast(T, instance)
                 if state_type is dict:
-                    return cast(T, {"id": str(uuid4())})
+                    state_dict = {"id": str(uuid4())}
+                    state_dict.update(kwargs)
+                    return cast(T, state_dict)
 
         # Handle case where no initial state is provided
         if self.initial_state is None:
-            return cast(T, {"id": str(uuid4())})
+            state_dict = {"id": str(uuid4())}
+            state_dict.update(kwargs)
+            return cast(T, state_dict)
 
         # Handle case where initial_state is a type (class)
         if isinstance(self.initial_state, type):
             if issubclass(self.initial_state, FlowState):
-                return cast(T, self.initial_state())  # Uses model defaults
+                return cast(T, self.initial_state(**kwargs))  # Uses model defaults and kwargs
             if issubclass(self.initial_state, BaseModel):
                 # Validate that the model has an id field
                 model_fields = getattr(self.initial_state, "model_fields", None)
                 if not model_fields or "id" not in model_fields:
                     raise ValueError("Flow state model must have an 'id' field")
-                return cast(T, self.initial_state())  # Uses model defaults
+                return cast(T, self.initial_state(**kwargs))  # Uses model defaults and kwargs
             if self.initial_state is dict:
-                return cast(T, {"id": str(uuid4())})
+                state_dict = {"id": str(uuid4())}
+                state_dict.update(kwargs)
+                return cast(T, state_dict)
 
         # Handle dictionary instance case
         if isinstance(self.initial_state, dict):
             new_state = dict(self.initial_state)  # Copy to avoid mutations
             if "id" not in new_state:
                 new_state["id"] = str(uuid4())
+            new_state.update(kwargs)  # Apply kwargs
             return cast(T, new_state)
 
         # Handle BaseModel instance case
@@ -652,6 +662,8 @@ class Flow(Generic[T], metaclass=FlowMeta):
                     k: v for k, v in model.__dict__.items() if not k.startswith("_")
                 }
 
+            state_dict.update(kwargs)
+            
             # Create new instance of the same class
             model_class = type(model)
             return cast(T, model_class(**state_dict))

tests/test_flow_pydantic_required_fields.py

@@ -0,0 +1,145 @@
+"""Tests for Flow initialization with Pydantic models having required fields.
+Covers https://github.com/crewAIInc/crewAI/issues/3744
+"""
+
+import pytest
+from pydantic import BaseModel, ValidationError
+
+from crewai.flow.flow import Flow, FlowState, listen, start
+
+
+class RequiredState(BaseModel):
+    """State model with required fields."""
+    name: str
+    age: int
+
+
+class RequiredStateFlow(Flow[RequiredState]):
+    """Flow with required state fields."""
+    
+    @start()
+    def begin(self):
+        return "started"
+
+
+class MixedState(BaseModel):
+    """State model with both required and optional fields."""
+    name: str  # Required
+    age: int  # Required
+    email: str = "default@example.com"  # Optional with default
+
+
+class MixedStateFlow(Flow[MixedState]):
+    """Flow with mixed required and optional state fields."""
+    
+    @start()
+    def begin(self):
+        return f"Started with {self.state.name}, {self.state.age}, {self.state.email}"
+
+
+class RequiredStateWithFlowState(FlowState):
+    """State model extending FlowState with required fields."""
+    name: str
+    age: int
+
+
+class RequiredFlowStateFlow(Flow[RequiredStateWithFlowState]):
+    """Flow with required FlowState fields."""
+    
+    @start()
+    def begin(self):
+        return "started"
+
+
+def test_flow_initialization_without_kwargs_raises_validation_error():
+    """Test that Flow initialization without kwargs raises ValidationError for required fields."""
+    with pytest.raises(ValidationError) as exc_info:
+        RequiredStateFlow()
+    
+    error_str = str(exc_info.value)
+    assert "name" in error_str
+    assert "age" in error_str
+
+
+def test_flow_initialization_with_kwargs_passes_and_sets_state():
+    """Test that Flow initialization with kwargs properly sets state values."""
+    flow = RequiredStateFlow(name="John", age=30)
+    assert flow.state.name == "John"
+    assert flow.state.age == 30
+    assert hasattr(flow.state, "id")
+    assert flow.state.id is not None
+
+
+def test_flow_initialization_with_partial_kwargs_raises_validation_error():
+    """Test that Flow initialization with only some required kwargs raises ValidationError."""
+    with pytest.raises(ValidationError) as exc_info:
+        RequiredStateFlow(name="John")
+    
+    error_str = str(exc_info.value)
+    assert "age" in error_str
+
+
+def test_flow_initialization_with_mixed_required_and_optional_fields():
+    """Test Flow initialization with both required and optional fields."""
+    flow1 = MixedStateFlow(name="Alice", age=25)
+    assert flow1.state.name == "Alice"
+    assert flow1.state.age == 25
+    assert flow1.state.email == "default@example.com"
+    
+    flow2 = MixedStateFlow(name="Bob", age=35, email="bob@example.com")
+    assert flow2.state.name == "Bob"
+    assert flow2.state.age == 35
+    assert flow2.state.email == "bob@example.com"
+
+
+def test_flow_initialization_with_flowstate_and_required_fields():
+    """Test Flow initialization with FlowState subclass having required fields."""
+    flow = RequiredFlowStateFlow(name="Charlie", age=40)
+    assert flow.state.name == "Charlie"
+    assert flow.state.age == 40
+    assert hasattr(flow.state, "id")
+    assert flow.state.id is not None
+
+
+def test_flow_execution_with_required_state():
+    """Test that Flow execution works correctly with required state fields."""
+    flow = RequiredStateFlow(name="David", age=45)
+    result = flow.kickoff()
+    assert result == "started"
+    assert flow.state.name == "David"
+    assert flow.state.age == 45
+
+
+def test_flow_with_state_modification():
+    """Test that state can be modified during flow execution."""
+    
+    class ModifiableState(BaseModel):
+        counter: int
+        name: str
+    
+    class ModifiableFlow(Flow[ModifiableState]):
+        @start()
+        def increment(self):
+            self.state.counter += 10
+            return "incremented"
+        
+        @listen(increment)
+        def check_value(self):
+            assert self.state.counter == 15
+            return "checked"
+    
+    flow = ModifiableFlow(counter=5, name="Test")
+    result = flow.kickoff()
+    assert result == "checked"
+    assert flow.state.counter == 15
+
+
+def test_flow_initialization_preserves_id_field():
+    """Test that the automatically generated id field is preserved."""
+    flow = RequiredStateFlow(name="Eve", age=28)
+    original_id = flow.state.id
+    
+    assert isinstance(original_id, str)
+    assert len(original_id) == 36  # UUID format with hyphens
+    
+    assert flow.state.id == original_id