[#1726][model] Harvest source reference compatibility

The 'source' property of harvest objects now comes from the actual
foreign key. For compatibility with old harvesters, an before insert
event listener has beeen added to check if the source id has been set,
and set it automatically from the job if not.
Note that this requires SQLAlchemy 0.7 (ie CKAN 1.5.1)

ckanext/harvest/model/__init__.py

@@ -1,6 +1,7 @@
 import logging
 import datetime
 
+from sqlalchemy import event
 from sqlalchemy import distinct
 from sqlalchemy.engine.reflection import Inspector
 from sqlalchemy.orm import backref, relation
@@ -120,10 +121,6 @@ class HarvestObject(HarvestDomainObject):
 
     '''
 
-    @property
-    def source(self):
-        return self.job.source
-
 class HarvestGatherError(HarvestDomainObject):
     '''Gather errors are raised during the **gather** stage of a harvesting
        job.
@@ -136,6 +133,18 @@ class HarvestObjectError(HarvestDomainObject):
     '''
     pass
 
+def harvest_object_before_insert_listener(mapper,connection,target):
+    '''
+        For compatibility with old harvesters, check if the source id has
+        been set, and set it automatically from the job if not.
+    '''
+    if not target.harvest_source_id or not target.source:
+        if not target.job:
+            raise Exception('You must define a Harvest Job for each Harvest Object')
+        target.source = target.job.source
+        target.harvest_source_id = target.job.source.id
+
+
 def define_harvester_tables():
 
     global harvest_source_table
@@ -228,6 +237,12 @@ def define_harvester_tables():
                 lazy=True,
                 backref=u'objects',
             ),
+            'source': relation(
+                HarvestSource,
+                lazy=True,
+                backref=u'objects',
+            ),
+
         },
     )
 
@@ -253,6 +268,7 @@ def define_harvester_tables():
         },
     )
 
+    event.listen(HarvestObject, 'before_insert', harvest_object_before_insert_listener)
 
 def migrate_v2():
     log.debug('Migrating harvest tables to v2. This may take a while...')