refine Tabulator fallback behaviour

- If field counts or names have changed, then fall back to Tabulator and start from scratch,
but if only the types have changed, then try to preserve the Data Dictionary and proceed with COPY.

Author: ThrawnCA

ckanext/xloader/jobs.py

@@ -21,7 +21,7 @@
 from ckan.plugins.toolkit import get_action, asbool, enqueue_job, ObjectNotFound, config, h
 
 from . import db, loader
-from .job_exceptions import JobError, HTTPError, DataTooBigError, FileCouldNotBeLoadedError, XLoaderTimeoutError
+from .job_exceptions import JobError, HTTPError, DataTooBigError, FileCouldNotBeLoadedError, LoaderError, XLoaderTimeoutError
 from .utils import datastore_resource_exists, set_resource_metadata, modify_input_url
 
 
@@ -257,11 +257,12 @@ def xloader_data_into_datastore_(input, job_dict, logger):
     logger.info('File hash: %s', file_hash)
     resource['hash'] = file_hash
 
-    def direct_load():
+    def direct_load(allow_type_guessing=False):
         fields = loader.load_csv(
             tmp_file.name,
             resource_id=resource['id'],
             mimetype=resource.get('format'),
+            allow_type_guessing=allow_type_guessing,
             logger=logger)
         loader.calculate_record_count(
             resource_id=resource['id'], logger=logger)
@@ -317,8 +318,8 @@ def tabulator_load():
                 direct_load()
         else:
             try:
-                direct_load()
-            except JobError as e:
+                direct_load(allow_type_guessing=True)
+            except (JobError, LoaderError) as e:
                 logger.warning('Load using COPY failed: %s', e)
                 logger.info('Trying again with tabulator')
                 tabulator_load()