Handle empty record sets during exporter job init

Rarely, an exporter job will run in which no qualifying records are
fetched from Sierra. Recent changes to tasks (JobPlan implementation,
etc.) did not take this into account, leading to the error described in
issue #46. This adds a check during job initialization and logs an
appropriate message if no records were found, bypassing the code path
that raised the error.

Author: jthomale

django/sierra/export/tasks.py

@@ -374,17 +374,6 @@ def _fetch_job_pk_lists(exp, plan):
     return pk_lists
 
 
-def _initialize_job_plan(exp, plan, pk_lists):
-    registry = plan.generate(pk_lists)
-    totals = plan.totals
-    total_op_chunks = totals['chunks_by_op']
-    exp.log('Info', 'Job plan initialized. {} total chunk(s) grouped into {} '
-                    'batch(es):'.format(totals['chunks'], totals['batches']))
-    for op in plan.operations:
-        exp.log('Info', '   {}, {} chunk(s)'.format(op, total_op_chunks[op]))
-    return plan
-
-
 def _apply_pk_sort_order(qset):
     if hasattr(qset.model, 'record_metadata'):
         return qset.order_by('record_metadata__record_last_updated_gmt', 'pk')
@@ -435,9 +424,15 @@ def delegate_batch(vals_list, instance_pk, export_filter, export_type, options,
         pk_lists = _fetch_job_pk_lists(exp, plan)
         exp.log('Info', 'Initializing job plan.')
         plan.generate(pk_lists)
-        exp.log('Info', _hr_line())
-        plan.log_plan_summary(exp)
-        exp.log('Info', _hr_line())
+        if plan.registry:
+            exp.log('Info', _hr_line())
+            plan.log_plan_summary(exp)
+            exp.log('Info', _hr_line())
+        else:
+            msg = ('No records found for {}. Nothing to do!'
+                   ''.format(', '.join(pk_lists.keys())))
+            exp.log('Info', msg)
+        
 
     elif prev_batch_had_errors:
         vals_list = _compile_vals_list_for_batch(prev_batch_task_id)
@@ -455,7 +450,7 @@ def delegate_batch(vals_list, instance_pk, export_filter, export_type, options,
             exp.options)
 
     batch_tasks = []
-    for task_chunk_id in plan.registry[batch_id]:
+    for task_chunk_id in plan.registry.get(batch_id, []):
         kwargs = {'chunk_id': task_chunk_id}
         batch_tasks.append(do_export_chunk.s(cumulative_vals, *args, **kwargs))