postAggregators now return field dependencies

client/src/main/java/com/metamx/druid/query/Queries.java

@@ -20,6 +20,7 @@
 package com.metamx.druid.query;
 
 import com.google.common.base.Function;
+import com.google.common.base.Joiner;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
@@ -27,6 +28,7 @@ import com.metamx.druid.aggregation.AggregatorFactory;
 import com.metamx.druid.aggregation.post.PostAggregator;
 
 import javax.annotation.Nullable;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -58,9 +60,12 @@ public class Queries
       );
 
       for (PostAggregator postAgg : postAggs) {
+        Set<String> dependencies = postAgg.getDependentFields();
+        Set<String> missing = Sets.difference(dependencies, combinedAggNames);
+
         Preconditions.checkArgument(
-            postAgg.verifyFields(combinedAggNames),
+            missing.isEmpty(),
-            String.format("Missing field[%s]", postAgg.getName())
+            String.format("Missing fields [%s] for postAggregator [%s]", Joiner.on(",").join(missing), postAgg.getName())
         );
         combinedAggNames.add(postAgg.getName());
       }

common/src/main/java/com/metamx/druid/aggregation/post/ArithmeticPostAggregator.java

@@ -20,6 +20,7 @@
 package com.metamx.druid.aggregation.post;
 
 import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
 import com.metamx.common.IAE;
 import org.codehaus.jackson.annotate.JsonCreator;
 import org.codehaus.jackson.annotate.JsonProperty;
@@ -69,14 +70,13 @@ public class ArithmeticPostAggregator implements PostAggregator
   }
 
   @Override
-  public boolean verifyFields(Set<String> fieldNames)
+  public Set<String> getDependentFields()
   {
+    Set<String> dependentFields = Sets.newHashSet();
     for (PostAggregator field : fields) {
-      if (!field.verifyFields(fieldNames)) {
+      dependentFields.addAll(field.getDependentFields());
-        return false;
-      }
     }
-    return true;
+    return dependentFields;
   }
 
   @Override

common/src/main/java/com/metamx/druid/aggregation/post/ConstantPostAggregator.java

@@ -19,6 +19,7 @@
 
 package com.metamx.druid.aggregation.post;
 
+import com.google.common.collect.Sets;
 import org.codehaus.jackson.annotate.JsonCreator;
 import org.codehaus.jackson.annotate.JsonProperty;
 
@@ -44,9 +45,9 @@ public class ConstantPostAggregator implements PostAggregator
   }
 
   @Override
-  public boolean verifyFields(Set<String> fields)
+  public Set<String> getDependentFields()
   {
-    return true;
+    return Sets.newHashSet();
   }
 
   @Override

common/src/main/java/com/metamx/druid/aggregation/post/FieldAccessPostAggregator.java

@@ -19,6 +19,7 @@
 
 package com.metamx.druid.aggregation.post;
 
+import com.google.common.collect.Sets;
 import com.metamx.common.ISE;
 import org.codehaus.jackson.annotate.JsonCreator;
 import org.codehaus.jackson.annotate.JsonProperty;
@@ -45,9 +46,9 @@ public class FieldAccessPostAggregator implements PostAggregator
   }
 
   @Override
-  public boolean verifyFields(Set<String> fieldNames)
+  public Set<String> getDependentFields()
   {
-    return fieldNames.contains(fieldName);
+    return Sets.newHashSet(fieldName);
   }
 
   @Override

common/src/main/java/com/metamx/druid/aggregation/post/PostAggregator.java

@@ -37,7 +37,7 @@ import java.util.Set;
 })
 public interface PostAggregator
 {
-  public boolean verifyFields(Set<String> fieldNames);
+  public Set<String> getDependentFields();
 
   public Comparator getComparator();