protect future_task foreign key add operation from running when bad data (#1770)

Co-authored-by: burnettk <burnettk@users.noreply.github.com>

spiffworkflow-backend/migrations/versions/7eaec0e12079_.py

@@ -7,6 +7,8 @@ Create Date: 2024-06-18 16:45:06.102210
 """
 from alembic import op
 import sqlalchemy as sa
+from sqlalchemy import text
+from spiffworkflow_backend.models.db import dialect_name
 
 
 # revision identifiers, used by Alembic.
@@ -15,16 +17,46 @@ down_revision = '43afc70a7016'
 branch_labels = None
 depends_on = None
 
+def delete_orphaned_future_tasks() -> None:
+    # Ensure database connection
+    conn = op.get_bind()
 
-def upgrade():
-    # ### commands auto generated by Alembic - please adjust! ###
+    dialect = dialect_name()
+
+    if dialect == "mysql":
+        delete_query = text("""
+            DELETE future_task FROM future_task
+            LEFT JOIN task ON future_task.guid = task.guid
+            WHERE task.guid IS NULL;
+        """)
+    elif dialect == "postgresql":
+        delete_query = text("""
+            DELETE FROM future_task
+            USING task
+            WHERE future_task.guid = task.guid
+            AND task.guid IS NULL;
+        """)
+    elif dialect == "sqlite":
+        delete_query = text("""
+            DELETE FROM future_task
+            WHERE guid NOT IN (
+                SELECT guid FROM task
+            );
+        """)
+    else:
+        raise ValueError(f"Unsupported database dialect: {dialect}")
+
+    # Execute the delete query
+    conn.execute(delete_query)
+
+
+def upgrade() -> None:
+    delete_orphaned_future_tasks()
     with op.batch_alter_table('future_task', schema=None) as batch_op:
         batch_op.create_foreign_key('future_task_task_guid_fk', 'task', ['guid'], ['guid'], ondelete='CASCADE')
 
-    # ### end Alembic commands ###
 
-
-def downgrade():
+def downgrade() -> None:
     # ### commands auto generated by Alembic - please adjust! ###
     with op.batch_alter_table('future_task', schema=None) as batch_op:
         batch_op.drop_constraint('future_task_task_guid_fk', type_='foreignkey')