Make it possible to reach the bottommost writer

apps/cli/utilities/core_sampler/core_sampler/core_sampler.py

@@ -132,7 +132,7 @@ class CoreSampler:
         requested = projects.fetch({"science_product_locator": science_product_locator})
         self.save(requested)
         self.writer.close()
-        return self.writer
+        return self.writer.bottom()
 
     def sample_project(self, project_code: str) -> RowWriter:
         """
@@ -147,7 +147,7 @@ class CoreSampler:
         requested = projects.fetch({"project_code": project_code})
         self.save(requested)
         self.writer.close()
-        return self.writer
+        return self.writer.bottom()
 
     def sample_eb(self, sdm_name: str) -> RowWriter:
         """
@@ -163,7 +163,7 @@ class CoreSampler:
         requested = ebs.fetch({"execution_block_id": eb_id})
         self.save(requested)
         self.writer.close()
-        return self.writer
+        return self.writer.bottom()
 
     def save(self, rows: RowSet):
         """

apps/cli/utilities/core_sampler/core_sampler/interfaces.py

@@ -74,6 +74,9 @@ class Table(ABC):
 
 
 class RowWriter:
+    def bottom(self) -> "RowWriter":
+        return self
+
     def write_rows(self, table: Table, rows: List[Dict]):
         raise NotImplementedError
 

apps/cli/utilities/core_sampler/core_sampler/row_writer.py

@@ -78,6 +78,9 @@ class UniquifyingRowWriter(RowWriter):
         self.underlying = underlying
         self.seen = {}
 
+    def bottom(self) -> "RowWriter":
+        return self.underlying.bottom()
+
     def write_rows(self, table: "Table", rows: List[Dict]):
         seen = self.seen.setdefault(table.name, [])
         new_rows = [row for row in rows if row not in seen]
@@ -114,6 +117,9 @@ class TopologicallySortingRowWriter(RowWriter):
         self.tables_rows: Dict["Table", List[Dict]] = {}
         self.underlying = underlying
 
+    def bottom(self) -> "RowWriter":
+        return self.underlying.bottom()
+
     def write_rows(self, table: "Table", rows: List[Dict]):
         # We've been asked to output some rows for this table.
         # What we must now do is keep track of this table and the in-bound relationships with it.