Add data migration for multi-chamber support

representatives/migrations/0016_chamber_migrate_data.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+import hashlib
+
+from django.db import migrations, models
+from django.utils.encoding import smart_str
+
+
+def calculate_hash(obj):
+    """
+    Computes fingerprint for an object, this code is duplicated from
+    representatives.models.HashableModel because we don't have access to model
+    methods in a migration scenario.
+    """
+
+    hashable_fields = {
+        'Chamber': ['name', 'country', 'abbreviation'],
+        'Constituency': ['name'],
+        'Group': ['name', 'abbreviation', 'kind', 'chamber'],
+        'Mandate': ['group', 'constituency', 'role', 'begin_date', 'end_date',
+            'representative']
+    }
+
+    fingerprint = hashlib.sha1()
+    for field_name in hashable_fields[obj.__class__.__name__]:
+        field = obj._meta.get_field(field_name)
+        if field.is_relation:
+            related = getattr(obj, field_name)
+            if related is None:
+                fingerprint.update(smart_str(related))
+            else:
+                fingerprint.update(related.fingerprint)
+        else:
+            fingerprint.update(smart_str(getattr(obj, field_name)))
+    obj.fingerprint = fingerprint.hexdigest()
+    return obj.fingerprint
+
+
+def get_or_create(cls, **kwargs):
+    """
+    Implements get_or_create logic for models that inherit from
+    representatives.models.HashableModel because we don't have access to model
+    methods in a migration scenario.
+    """
+
+    try:
+        obj = cls.objects.get(**kwargs)
+        created = False
+    except cls.DoesNotExist:
+        obj = cls(**kwargs)
+        created = True
+        calculate_hash(obj)
+        obj.save()
+
+    return (obj, created)
+
+
+def migrate_ep_chamber(apps, schema_editor):
+    # Get model managers
+
+    Chamber = apps.get_model("representatives", "Chamber")
+    Constituency = apps.get_model("representatives", "Constituency")
+    Group = apps.get_model("representatives", "Group")
+    Mandate = apps.get_model("representatives", "Mandate")
+
+    # Create EP chamber, constituency and group
+
+    name = 'European Parliament'
+    abbr = 'EP'
+
+    ep_chamber, _ = get_or_create(Chamber, name=name, abbreviation=abbr)
+    ep_constituency, _ = get_or_create(Constituency, name=name)
+    ep_group, _ = get_or_create(Group, name=name, kind='chamber',
+        abbreviation=abbr, chamber=ep_chamber)
+
+    # Set chamber on groups
+
+    ep_group_kinds = [
+        'committee',
+        'delegation',
+        'group'
+    ]
+
+    Group.objects.filter(kind__in=ep_group_kinds).update(chamber=ep_chamber)
+
+    # Set constituency on EP mandates
+
+    ep_mandate_kinds = [
+        'committee',
+        'delegation',
+        'group',
+        'organization'
+    ]
+
+    Mandate.objects.filter(group__kind__in=ep_mandate_kinds).update(
+        constituency=ep_constituency)
+
+    # Create EP mandates with EP constituency & group with same timespan as
+    # the country mandate
+
+    for m in Mandate.objects.filter(group__kind__exact='country'):
+        mandate, _ = get_or_create(Mandate,
+            representative=m.representative,
+            group=ep_group,
+            constituency=ep_constituency,
+            role=m.role,
+            begin_date=m.begin_date,
+            end_date=m.end_date
+        )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('representatives', '0015_chamber_abbreviation'),
+    ]
+
+    operations = [
+        migrations.RunPython(migrate_ep_chamber)
+    ]