[Issue #2405] Account for updates when last_upd_date is null (#2406)

## Summary
Fixes #2405

### Time to review: __5 mins__

## Changes proposed
Fallback to using `created_date` when `last_upd_date` is null

## Context for reviewers
The legacy Oracle database has a last_upd_date timestamp that we use for
finding updates to our system.

This field is always null when a record is first inserted, and only on
receiving at least one update will it be populated.

This means that if a record is inserted, we copy over last_upd_date=null
and then an update happens, we try to do effectively: where null < {some
timestamp} which means we find nothing when trying to update. What we
instead should do is fallback to using the created_date timestamp if the
update date is null.

## Additional information
Found this when I realized there were cases where we just weren't
processing updates. Turns out, the ELT process doesn't handle updates
pretty much at all right now (this is the common case)

api/src/data_migration/load/sql.py

@@ -67,7 +67,15 @@ def build_select_updated_rows_sql(
             == sqlalchemy.tuple_(*source_table.primary_key.columns),
         )
         # `WHERE ...`
-        .where(destination_table.c.last_upd_date < source_table.c.last_upd_date)
+        # NOTE: The legacy system doesn't populate the last_upd_date unless at least one update
+        #       has occurred, so we need to fallback to the created_date otherwise it will always be
+        #       null on the destination table side
+        .where(
+            sqlalchemy.func.coalesce(
+                destination_table.c.last_upd_date, destination_table.c.created_date
+            )
+            < source_table.c.last_upd_date
+        )
         .order_by(*source_table.primary_key.columns)
     )
 

api/tests/src/data_migration/load/test_load_oracle_data_task.py

@@ -85,6 +85,9 @@ def test_load_data(self, db_session, foreign_tables, staging_tables, enable_fact
         source_record4 = ForeignTopportunityFactory.create(
             opportunity_id=4, oppnumber="A-4-update", cfdas=[], last_upd_date=time3
         )
+        source_record5 = ForeignTopportunityFactory.create(
+            opportunity_id=6, oppnumber="A-6-update", cfdas=[], last_upd_date=time3
+        )
 
         ## Destination records
         # unchanged:
@@ -95,6 +98,9 @@ def test_load_data(self, db_session, foreign_tables, staging_tables, enable_fact
         StagingTopportunityFactory.create(
             opportunity_id=4, oppnumber="A-4", cfdas=[], last_upd_date=time1
         )
+        StagingTopportunityFactory.create(
+            opportunity_id=6, oppnumber="A-6", cfdas=[], last_upd_date=None
+        )
         # delete:
         StagingTopportunityFactory.create(
             opportunity_id=5, oppnumber="A-5", cfdas=[], last_upd_date=time2
@@ -109,8 +115,8 @@ def test_load_data(self, db_session, foreign_tables, staging_tables, enable_fact
         # this prevents some weirdness with the value comparison we'll do
         db_session.expire_all()
 
-        assert db_session.query(source_table).count() == 4
-        assert db_session.query(destination_table).count() == 5
+        assert db_session.query(source_table).count() == 5
+        assert db_session.query(destination_table).count() == 6
 
         destination_records = (
             db_session.query(destination_table).order_by(destination_table.c.opportunity_id).all()
@@ -123,13 +129,14 @@ def test_load_data(self, db_session, foreign_tables, staging_tables, enable_fact
         )
         validate_copied_value(source_table, source_record4, destination_records[3])
         validate_copied_value(source_table, None, destination_records[4], is_delete=True)
+        validate_copied_value(source_table, source_record5, destination_records[5])
 
         assert task.metrics["count.delete.topportunity"] == 1
         assert task.metrics["count.insert.topportunity"] == 2
-        assert task.metrics["count.update.topportunity"] == 1
+        assert task.metrics["count.update.topportunity"] == 2
         assert task.metrics["count.delete.total"] == 1
         assert task.metrics["count.insert.total"] == 2
-        assert task.metrics["count.update.total"] == 1
+        assert task.metrics["count.update.total"] == 2
 
     def test_raises_if_table_dicts_different(self, db_session, foreign_tables, staging_tables):
         with pytest.raises(

api/tests/src/data_migration/load/test_sql.py

@@ -22,6 +22,7 @@ def source_table(sqlalchemy_metadata):
         sqlalchemy.Column("id2", sqlalchemy.Integer, primary_key=True),
         sqlalchemy.Column("x", sqlalchemy.Text),
         sqlalchemy.Column("last_upd_date", sqlalchemy.TIMESTAMP),
+        sqlalchemy.Column("created_date", sqlalchemy.TIMESTAMP),
     )
 
 
@@ -35,6 +36,7 @@ def destination_table(sqlalchemy_metadata):
         sqlalchemy.Column("x", sqlalchemy.Text),
         sqlalchemy.Column("is_deleted", sqlalchemy.Boolean),
         sqlalchemy.Column("last_upd_date", sqlalchemy.TIMESTAMP),
+        sqlalchemy.Column("created_date", sqlalchemy.TIMESTAMP),
     )
 
 
@@ -59,17 +61,17 @@ def test_build_select_updated_rows_sql(source_table, destination_table):
         "JOIN test_source_table ON "
         "(test_destination_table.id1, test_destination_table.id2) = "
         "(test_source_table.id1, test_source_table.id2) \n"
-        "WHERE test_destination_table.last_upd_date < test_source_table.last_upd_date "
+        "WHERE coalesce(test_destination_table.last_upd_date, test_destination_table.created_date) < test_source_table.last_upd_date "
         "ORDER BY test_source_table.id1, test_source_table.id2"
     )
 
 
 def test_build_insert_select_sql(source_table, destination_table):
     insert = sql.build_insert_select_sql(source_table, destination_table, [(1, 2), (3, 4), (5, 6)])
     assert str(insert) == (
-        "INSERT INTO test_destination_table (id1, id2, x, last_upd_date, is_deleted) "
+        "INSERT INTO test_destination_table (id1, id2, x, last_upd_date, created_date, is_deleted) "
         "SELECT test_source_table.id1, test_source_table.id2, test_source_table.x, "
-        "test_source_table.last_upd_date, FALSE AS is_deleted \n"
+        "test_source_table.last_upd_date, test_source_table.created_date, FALSE AS is_deleted \n"
         "FROM test_source_table \n"
         "WHERE (test_source_table.id1, test_source_table.id2) IN (__[POSTCOMPILE_param_1])"
     )
@@ -80,8 +82,8 @@ def test_build_update_sql(source_table, destination_table):
     assert str(update) == (
         "UPDATE test_destination_table "
         "SET id1=test_source_table.id1, id2=test_source_table.id2, x=test_source_table.x, "
-        "last_upd_date=test_source_table.last_upd_date FROM test_source_table "
-        "WHERE (test_destination_table.id1, test_destination_table.id2) = "
+        "last_upd_date=test_source_table.last_upd_date, created_date=test_source_table.created_date "
+        "FROM test_source_table WHERE (test_destination_table.id1, test_destination_table.id2) = "
         "(test_source_table.id1, test_source_table.id2) AND "
         "(test_source_table.id1, test_source_table.id2) "
         "IN (__[POSTCOMPILE_param_1])"