Move dynamic checking of which datasets a City supports to a DB field

The current dynamic check is not working very well. It checks for the
presence of map cells and reports their dataset names, but doesn't check
the values for those cells.
In practice, this means that a location without LOCA data will be reported
as supporting LOCA data, as the ingest will create LOCA cells, but fill
them with NaN (not a number) values.

Since checking the values in each cell would be computationally expensive,
we've instead moved the list of supported datasets to be stored in the
database. A future enhancement (#823) will ensure that this is properly
set for every existing city.

Closes #822

django/climate_change_api/climate_change_api/settings.py

@@ -70,6 +70,7 @@
     'django.contrib.admin',
     'django.contrib.auth',
     'django.contrib.contenttypes',
+    'django.contrib.gis',
     'django.contrib.sessions',
     'django.contrib.messages',
     'django.contrib.staticfiles',

django/climate_change_api/climate_data/admin.py

@@ -0,0 +1,10 @@
+from django.contrib import admin
+
+from climate_data.models import City
+
+
+class CityAdmin(admin.ModelAdmin):
+    exclude = ('_geog',)
+
+
+admin.site.register(City, CityAdmin)

django/climate_change_api/climate_data/migrations/0066_auto_20180627_2016.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.8 on 2018-06-27 20:16
+from __future__ import unicode_literals
+
+import climate_data.models
+import django.contrib.postgres.fields
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('climate_data', '0065_scenario_alias'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='city',
+            options={'verbose_name_plural': 'cities'},
+        ),
+        migrations.AddField(
+            model_name='city',
+            name='datasets',
+            field=django.contrib.postgres.fields.ArrayField(base_field=models.CharField(choices=[('LOCA', 'LOCA'), ('NEX-GDDP', 'NEX-GDDP')], max_length=48), default=climate_data.models.get_datasets, size=2),
+        ),
+        migrations.AlterField(
+            model_name='climatedataset',
+            name='name',
+            field=models.CharField(choices=[('LOCA', 'LOCA'), ('NEX-GDDP', 'NEX-GDDP')], max_length=48, unique=True),
+        ),
+    ]

django/climate_change_api/climate_data/models.py

@@ -1,6 +1,6 @@
 from django.contrib.gis.db import models
 from django.contrib.postgres.fields.array import ArrayField
-from django.core.exceptions import ObjectDoesNotExist
+from django.core.exceptions import ObjectDoesNotExist, ValidationError
 from django.db.models import CASCADE, SET_NULL
 
 from climate_data.geo_boundary import census
@@ -16,10 +16,23 @@ def db_type(self, connection):
         return models.SmallIntegerField().db_type(connection=connection)
 
 
+def get_datasets():
+    return [ClimateDataset.Datasets.LOCA, ClimateDataset.Datasets.NEX_GDDP]
+
+
 class ClimateDataset(models.Model):
     """Model representing a particular climate projection dataset."""
 
-    name = models.CharField(max_length=48, unique=True)
+    class Datasets:
+        LOCA = 'LOCA'
+        NEX_GDDP = 'NEX-GDDP'
+
+        CHOICES = (
+            (LOCA, LOCA),
+            (NEX_GDDP, NEX_GDDP),
+        )
+
+    name = models.CharField(max_length=48, unique=True, choices=Datasets.CHOICES)
     label = models.CharField(max_length=128, blank=True, null=True)
     description = models.CharField(max_length=4096, blank=True, null=True)
     url = models.URLField(blank=True, null=True)
@@ -286,6 +299,12 @@ class City(models.Model):
     is_coastal = models.BooleanField(default=False)
     population = models.IntegerField(null=True)
 
+    datasets = ArrayField(
+        models.CharField(max_length=48, choices=ClimateDataset.Datasets.CHOICES),
+        size=2,
+        default=get_datasets
+    )
+
     region = models.ForeignKey(Region, on_delete=SET_NULL, null=True)
 
     objects = CityManager()
@@ -296,6 +315,7 @@ def __str__(self):
 
     class Meta:
         unique_together = ('name', 'admin')
+        verbose_name_plural = 'cities'
 
     def get_map_cell(self, dataset):
         """Get the map cell for a given dataset for a given city.
@@ -309,6 +329,11 @@ def get_map_cell(self, dataset):
     def natural_key(self):
         return (self.name, self.admin)
 
+    def clean(self):
+        super().clean()
+        if len(self.datasets) != len(set(self.datasets)):
+            raise ValidationError({'datasets': 'Cannot contain duplicate datasets'})
+
     def save(self, *args, **kwargs):
         """Override save to keep the geography field up to date."""
         self._geog = self.geom

django/climate_change_api/climate_data/serializers.py

@@ -62,11 +62,6 @@ class Meta:
 
 class CitySerializer(GeoFeatureModelSerializer):
 
-    datasets = serializers.SerializerMethodField()
-
-    def get_datasets(self, obj):
-        return [map_cell.dataset.name for map_cell in obj.map_cell_set.select_related('dataset')]
-
     proximity = serializers.SerializerMethodField()
 
     def get_proximity(self, obj):

django/climate_change_api/climate_data/views.py

@@ -155,9 +155,7 @@ def datasets(self, request, pk=None):
         Returns 404 if the city object has no valid map cells.
         """
         city = self.get_object()
-        map_cells = ClimateDataCityCell.objects.filter(city=city)
-        response = [map_cell.dataset.name for map_cell in map_cells]
-        return Response(response, status=status.HTTP_200_OK)
+        return Response(city.datasets, status=status.HTTP_200_OK)
 
 
 class CityMapCellListView(APIView):