Add element type property to LinkableElement interface (#1226)

The LinkableElement interface is used in cases where we have a
set of LinkableElements undifferentiated by underlying type.
In predicate pushdown, this happens with where specs that reference
some set of linkable elements but store them in an undifferentiated
collection.

In practice, we need to know not just the object type, but the more
refined LinkableElementType in order to apply the pushdown evaluation
logic, as time dimensions and categorical dimensions need to be
considered in a distinct way.

This makes the relevant property available in the parent interface
so we can access it directly.

metricflow-semantics/metricflow_semantics/model/semantics/linkable_element.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import logging
-from abc import ABC
+from abc import ABC, abstractmethod
 from dataclasses import dataclass
 from enum import Enum
 from typing import FrozenSet, Optional, Sequence, Tuple
@@ -98,7 +98,11 @@ class SemanticModelJoinPathElement:
 class LinkableElement(SemanticModelDerivation, SerializableDataclass, ABC):
     """An entity / dimension that may have been joined by entities."""
 
-    pass
+    @property
+    @abstractmethod
+    def element_type(self) -> LinkableElementType:
+        """The LinkableElementType describing what this instance represents."""
+        raise NotImplementedError
 
 
 @dataclass(frozen=True)
@@ -116,15 +120,19 @@ class LinkableDimension(LinkableElement, SerializableDataclass):
     date_part: Optional[DatePart]
 
     @property
-    def path_key(self) -> ElementPathKey:  # noqa: D102
-        if self.dimension_type is DimensionType.CATEGORICAL:
-            element_type = LinkableElementType.DIMENSION
-        else:
-            element_type = LinkableElementType.TIME_DIMENSION
+    @override
+    def element_type(self) -> LinkableElementType:
+        return (
+            LinkableElementType.DIMENSION
+            if self.dimension_type is DimensionType.CATEGORICAL
+            else LinkableElementType.TIME_DIMENSION
+        )
 
+    @property
+    def path_key(self) -> ElementPathKey:  # noqa: D102
         return ElementPathKey(
             element_name=self.element_name,
-            element_type=element_type,
+            element_type=self.element_type,
             entity_links=self.entity_links,
             time_granularity=self.time_granularity,
             date_part=self.date_part,
@@ -156,10 +164,15 @@ class LinkableEntity(LinkableElement, SerializableDataclass):
     entity_links: Tuple[EntityReference, ...]
     join_path: SemanticModelJoinPath
 
+    @property
+    @override
+    def element_type(self) -> LinkableElementType:
+        return LinkableElementType.ENTITY
+
     @property
     def path_key(self) -> ElementPathKey:  # noqa: D102
         return ElementPathKey(
-            element_name=self.element_name, element_type=LinkableElementType.ENTITY, entity_links=self.entity_links
+            element_name=self.element_name, element_type=self.element_type, entity_links=self.entity_links
         )
 
     @property
@@ -199,6 +212,11 @@ def __post_init__(self) -> None:
         """
         assert {LinkableElementProperty.METRIC, LinkableElementProperty.JOINED}.issubset(self.properties)
 
+    @property
+    @override
+    def element_type(self) -> LinkableElementType:
+        return LinkableElementType.METRIC
+
     @property
     def element_name(self) -> str:  # noqa: D102
         return self.reference.element_name
@@ -207,7 +225,7 @@ def element_name(self) -> str:  # noqa: D102
     def path_key(self) -> ElementPathKey:  # noqa: D102
         return ElementPathKey(
             element_name=self.element_name,
-            element_type=LinkableElementType.METRIC,
+            element_type=self.element_type,
             entity_links=self.join_path.entity_links,
             metric_subquery_entity_links=self.metric_subquery_entity_links,
         )