feat: Feast proto & pydantic model changes to add defaultvalue to field

protos/feast/core/Feature.proto

@@ -45,4 +45,7 @@ message FeatureSpecV2 {
 
     // Field indicating the vector length
     int32 vector_length = 7;
+
+    // Default value to be used for the feature when its value is missing/expired.
+    feast.types.Value default_value = 8;
 }

protos/feast/serving/ServingService.proto

@@ -108,6 +108,16 @@ message GetOnlineFeaturesRequest {
 
     // Whether to include the timestamp/status metadata in the response
     bool include_metadata = 10;
+
+    // Mode for handling features with default values when feature value is missing
+    UseDefaultsMode use_defaults = 11;
+}
+
+enum UseDefaultsMode {
+      USE_DEFAULTS_UNSPECIFIED = 0; // Field not set - use server default behavior (currently OFF)
+      USE_DEFAULTS_OFF = 1;        // Explicitly disable default replacement
+      USE_DEFAULTS_FLEXIBLE = 2;   // Ignore if default missing
+      USE_DEFAULTS_STRICT = 3;     // Fail if default is missing
 }
 
 message GetOnlineFeaturesResponse {
@@ -200,6 +210,10 @@ message GetOnlineFeaturesRangeRequest {
 
     // Whether to include the timestamp and status metadata in the response
     bool include_metadata = 9;
+
+    // Mode for handling features with default values when feature value is missing
+    UseDefaultsMode use_defaults = 11;
+
 }
 
 message GetOnlineFeaturesRangeResponse {

sdk/python/feast/expediagroup/pydantic_models/field_model.py

@@ -1,9 +1,10 @@
 from typing import Dict, Optional, Union
 
-from pydantic import BaseModel
+from pydantic import BaseModel, ConfigDict
 from typing_extensions import Self
 
 from feast.field import Field
+from feast.protos.feast.types import Value_pb2 as ValueProto
 from feast.types import Array, PrimitiveFeastType
 
 
@@ -19,6 +20,9 @@ class FieldModel(BaseModel):
     vector_index: bool = False
     vector_length: int = 0
     vector_search_metric: Optional[str] = None
+    default_value: Optional[ValueProto.Value] = None
+
+    model_config = ConfigDict(arbitrary_types_allowed=True)
 
     def to_field(self) -> Field:
         """
@@ -35,6 +39,7 @@ def to_field(self) -> Field:
             vector_index=self.vector_index,
             vector_length=self.vector_length,
             vector_search_metric=self.vector_search_metric,
+            default_value=self.default_value,
         )
 
     @classmethod
@@ -56,4 +61,5 @@ def from_field(
             vector_index=field.vector_index,
             vector_length=field.vector_length,
             vector_search_metric=field.vector_search_metric,
+            default_value=field.default_value,
         )

sdk/python/feast/feature.py

@@ -15,6 +15,7 @@
 from typing import Dict, Optional
 
 from feast.protos.feast.core.Feature_pb2 import FeatureSpecV2 as FeatureSpecProto
+from feast.protos.feast.types import Value_pb2 as ValueProto
 from feast.protos.feast.types.Value_pb2 import ValueType as ValueTypeProto
 from feast.value_type import ValueType
 
@@ -35,6 +36,7 @@ def __init__(
         dtype: ValueType,
         description: str = "",
         labels: Optional[Dict[str, str]] = None,
+        default_value: Optional[ValueProto.Value] = None,
     ):
         """Creates a Feature object."""
         self._name = name
@@ -48,6 +50,7 @@ def __init__(
             self._labels = dict()
         else:
             self._labels = labels
+        self._default_value = default_value
 
     def __eq__(self, other):
         if self.name != other.name or self.dtype != other.dtype:
@@ -64,6 +67,7 @@ def __repr__(self):
             f"    dtype={self._dtype!r},\n"
             f"    description={self._description!r},\n"
             f"    labels={self._labels!r}\n"
+            f"    default_value={self._default_value!r}\n"
             f")"
         )
 
@@ -99,6 +103,13 @@ def labels(self) -> Dict[str, str]:
         """
         return self._labels
 
+    @property
+    def default_value(self) -> Optional[ValueProto.Value]:
+        """
+        Gets the default value of this feature.
+        """
+        return self._default_value
+
     def to_proto(self) -> FeatureSpecProto:
         """
         Converts Feature object to its Protocol Buffer representation.
@@ -108,12 +119,15 @@ def to_proto(self) -> FeatureSpecProto:
         """
         value_type = ValueTypeProto.Enum.Value(self.dtype.name)
 
-        return FeatureSpecProto(
+        proto = FeatureSpecProto(
             name=self.name,
             value_type=value_type,
             description=self.description,
             tags=self.labels,
         )
+        if self.default_value is not None:
+            proto.default_value.CopyFrom(self.default_value)  # type: ignore[attr-defined]
+        return proto
 
     @classmethod
     def from_proto(cls, feature_proto: FeatureSpecProto):
@@ -124,11 +138,16 @@ def from_proto(cls, feature_proto: FeatureSpecProto):
         Returns:
             Feature object
         """
+        default_value = getattr(feature_proto, "default_value", None)
+        if default_value is not None and not default_value.WhichOneof("val"):
+            # Empty Value proto, treat as None
+            default_value = None
         feature = cls(
             name=feature_proto.name,
             dtype=ValueType(feature_proto.value_type),
             description=feature_proto.description,
             labels=dict(feature_proto.tags),
+            default_value=default_value,
         )
 
         return feature

sdk/python/feast/field.py

@@ -12,13 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Dict, Optional
+from typing import Any, Dict, Optional
 
 from pydantic import BaseModel, ConfigDict, field_validator
 from typeguard import check_type, typechecked
 
 from feast.feature import Feature
 from feast.protos.feast.core.Feature_pb2 import FeatureSpecV2 as FieldProto
+from feast.protos.feast.types import Value_pb2 as ValueProto
 from feast.types import FeastType, from_string, from_value_type
 from feast.value_type import ValueType
 
@@ -47,6 +48,61 @@ class Field(BaseModel):
     vector_index: bool = False
     vector_length: int = 0
     vector_search_metric: Optional[str] = ""
+    default_value: Optional[ValueProto.Value] = None
+
+    @field_validator("default_value")
+    @classmethod
+    def validate_default_value_type(
+        cls, v: Optional[ValueProto.Value], info: Any
+    ) -> Optional[ValueProto.Value]:
+        """
+        Validate that default_value type matches the field's dtype.
+        """
+        if v is None:
+            return v
+
+            # Get dtype from the model data
+        dtype = info.data.get("dtype")
+        if dtype is None:
+            # dtype will be validated by its own validator, skip for now
+            return v
+
+            # Validate type compatibility
+        value_type = dtype.to_value_type()
+        val_case = v.WhichOneof("val")
+
+        if val_case is None:
+            # Empty Value proto
+            return v
+
+            # Map proto value types to ValueType enums
+        type_mapping: Dict[str, ValueType] = {
+            "int32_val": ValueType.INT32,
+            "int64_val": ValueType.INT64,
+            "double_val": ValueType.DOUBLE,
+            "float_val": ValueType.FLOAT,
+            "string_val": ValueType.STRING,
+            "bytes_val": ValueType.BYTES,
+            "bool_val": ValueType.BOOL,
+            "unix_timestamp_val": ValueType.UNIX_TIMESTAMP,
+            "int32_list_val": ValueType.INT32_LIST,
+            "int64_list_val": ValueType.INT64_LIST,
+            "double_list_val": ValueType.DOUBLE_LIST,
+            "float_list_val": ValueType.FLOAT_LIST,
+            "string_list_val": ValueType.STRING_LIST,
+            "bytes_list_val": ValueType.BYTES_LIST,
+            "bool_list_val": ValueType.BOOL_LIST,
+            "unix_timestamp_list_val": ValueType.UNIX_TIMESTAMP_LIST,
+        }
+
+        expected_type = type_mapping.get(val_case)
+        if expected_type != value_type:
+            raise ValueError(
+                f"default_value type '{val_case}' does not match field dtype '{dtype}' "
+                f"(expected ValueType.{value_type.name})"
+            )
+
+        return v
 
     @field_validator("dtype", mode="before")
     def dtype_is_feasttype_or_string_feasttype(cls, v):
@@ -110,7 +166,7 @@ def to_proto(self) -> FieldProto:
         """Converts a Field object to its protobuf representation."""
         value_type = self.dtype.to_value_type()
         vector_search_metric = self.vector_search_metric or ""
-        return FieldProto(
+        proto = FieldProto(
             name=self.name,
             value_type=value_type.value,
             description=self.description,
@@ -119,6 +175,11 @@ def to_proto(self) -> FieldProto:
             vector_length=self.vector_length,
             vector_search_metric=vector_search_metric,
         )
+        # Add default_value if present (using type: ignore until proto is regenerated)
+        if self.default_value is not None:
+            proto.default_value.CopyFrom(self.default_value)  # type: ignore[attr-defined]
+
+        return proto
 
     @classmethod
     def from_proto(cls, field_proto: FieldProto):
@@ -132,6 +193,11 @@ def from_proto(cls, field_proto: FieldProto):
         vector_search_metric = getattr(field_proto, "vector_search_metric", "")
         vector_index = getattr(field_proto, "vector_index", False)
         vector_length = getattr(field_proto, "vector_length", 0)
+        # Extract default_value if present
+        default_value = getattr(field_proto, "default_value", None)
+        if default_value is not None and not default_value.WhichOneof("val"):
+            # Empty Value proto, treat as None
+            default_value = None
         return cls(
             name=field_proto.name,
             dtype=from_value_type(value_type=value_type),
@@ -140,6 +206,7 @@ def from_proto(cls, field_proto: FieldProto):
             vector_index=vector_index,
             vector_length=vector_length,
             vector_search_metric=vector_search_metric,
+            default_value=default_value,
         )
 
     @classmethod
@@ -155,4 +222,5 @@ def from_feature(cls, feature: Feature):
             dtype=from_value_type(feature.dtype),
             description=feature.description,
             tags=feature.labels,
+            default_value=feature.default_value,
         )

sdk/python/feast/protos/feast/core/Feature_pb2.pyi

@@ -56,6 +56,7 @@ class FeatureSpecV2(google.protobuf.message.Message):
     VECTOR_INDEX_FIELD_NUMBER: builtins.int
     VECTOR_SEARCH_METRIC_FIELD_NUMBER: builtins.int
     VECTOR_LENGTH_FIELD_NUMBER: builtins.int
+    DEFAULT_VALUE_FIELD_NUMBER: builtins.int
     name: builtins.str
     """Name of the feature. Not updatable."""
     value_type: feast.types.Value_pb2.ValueType.Enum.ValueType
@@ -71,6 +72,9 @@ class FeatureSpecV2(google.protobuf.message.Message):
     """Metric used for vector similarity search."""
     vector_length: builtins.int
     """Field indicating the vector length"""
+    @property
+    def default_value(self) -> feast.types.Value_pb2.Value:
+        """Default value to be used for the feature when its value is missing/expired."""
     def __init__(
         self,
         *,
@@ -81,7 +85,9 @@ class FeatureSpecV2(google.protobuf.message.Message):
         vector_index: builtins.bool = ...,
         vector_search_metric: builtins.str = ...,
         vector_length: builtins.int = ...,
+        default_value: feast.types.Value_pb2.Value | None = ...,
     ) -> None: ...
-    def ClearField(self, field_name: typing_extensions.Literal["description", b"description", "name", b"name", "tags", b"tags", "value_type", b"value_type", "vector_index", b"vector_index", "vector_length", b"vector_length", "vector_search_metric", b"vector_search_metric"]) -> None: ...
+    def HasField(self, field_name: typing_extensions.Literal["default_value", b"default_value"]) -> builtins.bool: ...
+    def ClearField(self, field_name: typing_extensions.Literal["default_value", b"default_value", "description", b"description", "name", b"name", "tags", b"tags", "value_type", b"value_type", "vector_index", b"vector_index", "vector_length", b"vector_length", "vector_search_metric", b"vector_search_metric"]) -> None: ...
 
 global___FeatureSpecV2 = FeatureSpecV2