catch empty return values and error on them

src/py/crankshaft/crankshaft/analysis_data_provider.py

@@ -2,18 +2,25 @@
 import plpy
 import pysal_utils as pu
 
+NULL_VALUE_ERROR = ('No usable data passed to analysis. Check your input rows '
+                    'for null values and fill in appropriately.')
+
+
+def verify_data(n_rows):
+    if n_rows == 0:
+        plpy.error(NULL_VALUE_ERROR)
+
 
 class AnalysisDataProvider:
     def get_getis(self, w_type, params):
         """fetch data for getis ord's g"""
         try:
             query = pu.construct_neighbor_query(w_type, params)
-            result = plpy.execute(query)
-            # if there are no neighbors, exit
-            if len(result) == 0:
-                return pu.empty_zipped_array(4)
-            else:
-                return result
+            data = plpy.execute(query)
+
+            # if there are no neighbors or all nulls, exit
+            verify_data(len(data))
+            return data
         except plpy.SPIError, err:
             plpy.error('Analysis failed: %s' % err)
 
@@ -23,9 +30,7 @@ class AnalysisDataProvider:
             query = pu.construct_neighbor_query(w_type, params)
             data = plpy.execute(query)
 
-            if len(data) == 0:
-                return pu.empty_zipped_array(4)
-
+            verify_data(len(data))
             return data
         except plpy.SPIError, err:
             plpy.error('Analysis failed: %s' % err)
@@ -37,8 +42,7 @@ class AnalysisDataProvider:
             data = plpy.execute(query)
 
             # if there are no neighbors, exit
-            if len(data) == 0:
-                return pu.empty_zipped_array(2)
+            verify_data(len(data))
             return data
         except plpy.SPIError, err:
             plpy.error('Analysis failed: %s' % e)
@@ -48,6 +52,7 @@ class AnalysisDataProvider:
         """fetch data for non-spatial kmeans"""
         try:
             data = plpy.execute(query)
+            verify_data(len(data))
             return data
         except plpy.SPIError, err:
             plpy.error('Analysis failed: %s' % err)
@@ -55,13 +60,14 @@ class AnalysisDataProvider:
     def get_spatial_kmeans(self, params):
         """fetch data for spatial kmeans"""
         query = ("SELECT "
-                 "array_agg({id_col} ORDER BY {id_col}) as ids,"
-                 "array_agg(ST_X({geom_col}) ORDER BY {id_col}) As xs,"
-                 "array_agg(ST_Y({geom_col}) ORDER BY {id_col}) As ys "
+                 "array_agg(\"{id_col}\" ORDER BY \"{id_col}\") as ids,"
+                 "array_agg(ST_X(\"{geom_col}\") ORDER BY \"{id_col}\") As xs,"
+                 "array_agg(ST_Y(\"{geom_col}\") ORDER BY \"{id_col}\") As ys "
                  "FROM ({subquery}) As a "
-                 "WHERE {geom_col} IS NOT NULL").format(**params)
+                 "WHERE \"{geom_col}\" IS NOT NULL").format(**params)
         try:
             data = plpy.execute(query)
+            verify_data(len(data))
             return data
         except plpy.SPIError, err:
             plpy.error('Analysis failed: %s' % err)