Better error message when buckets_path refers to multi-bucket agg

modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/InternalMatrixStats.java

@@ -201,7 +201,7 @@ public XContentBuilder doXContentBody(XContentBuilder builder, Params params) th
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else if (path.size() == 1) {

server/src/main/java/org/elasticsearch/search/aggregations/InternalAggregation.java

@@ -160,10 +160,16 @@ public boolean isMapped() {
      */
     public Object getProperty(String path) {
         AggregationPath aggPath = AggregationPath.parse(path);
-        return getProperty(aggPath.getPathElementsAsStringList());
+        return getProperty(aggPath.getPathElementsAsStringList(), true);
     }
 
-    public abstract Object getProperty(List<String> path);
+    /**
+     *
+     * @param path the path to the property in the aggregation tree
+     * @param allowMultiBucket true if multi-bucket aggregations are allowed to be processed, false if exception should be thrown
+     * @return the value of the property
+     */
+    public abstract Object getProperty(List<String> path, boolean allowMultiBucket);
 
     /**
      * Read a size under the assumption that a value of 0 means unlimited.

server/src/main/java/org/elasticsearch/search/aggregations/InternalMultiBucketAggregation.java

@@ -68,7 +68,13 @@ protected InternalMultiBucketAggregation(StreamInput in) throws IOException {
     public abstract List<? extends InternalBucket> getBuckets();
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
+        boolean needsBucketCount = path.isEmpty() == false && path.get(0).equals("_bucket_count") ? true : false;
+        if (allowMultiBucket == false && needsBucketCount == false) {
+            throw new AggregationExecutionException("[" + getName() + "] is a [" + getType()
+                + "], but only number value or a single value numeric metric aggregations are allowed.");
+        }
+
         if (path.isEmpty()) {
             return this;
         } else if (path.get(0).equals("_bucket_count")) {
@@ -119,6 +125,10 @@ public static int countInnerBucket(Aggregation agg) {
     public abstract static class InternalBucket implements Bucket, Writeable {
 
         public Object getProperty(String containingAggName, List<String> path) {
+            return getProperty(containingAggName, path, true);
+        }
+
+        public Object getProperty(String containingAggName, List<String> path, boolean allowMultiBucket) {
             if (path.isEmpty()) {
                 return this;
             }
@@ -140,7 +150,8 @@ public Object getProperty(String containingAggName, List<String> path) {
                 throw new InvalidAggregationPathException("Cannot find an aggregation named [" + aggName + "] in [" + containingAggName
                         + "]");
             }
-            return aggregation.getProperty(path.subList(1, path.size()));
+
+            return aggregation.getProperty(path.subList(1, path.size()), allowMultiBucket);
         }
     }
 }

server/src/main/java/org/elasticsearch/search/aggregations/bucket/InternalSingleBucketAggregation.java

@@ -22,8 +22,10 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.search.aggregations.Aggregation;
+import org.elasticsearch.search.aggregations.AggregationExecutionException;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.InternalAggregations;
+import org.elasticsearch.search.aggregations.InternalMultiBucketAggregation;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 
 import java.io.IOException;
@@ -110,7 +112,7 @@ public InternalAggregation doReduce(List<InternalAggregation> aggregations, Redu
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else {
@@ -125,7 +127,11 @@ public Object getProperty(List<String> path) {
             if (aggregation == null) {
                 throw new IllegalArgumentException("Cannot find an aggregation named [" + aggName + "] in [" + getName() + "]");
             }
-            return aggregation.getProperty(path.subList(1, path.size()));
+            if (allowMultiBucket == false && aggregation instanceof InternalMultiBucketAggregation) {
+                throw new AggregationExecutionException("[" + aggName + "] is a [" + aggregation.getType()
+                    + "], but only number value or a single value numeric metric aggregations are allowed.");
+            }
+            return aggregation.getProperty(path.subList(1, path.size()), allowMultiBucket);
         }
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalGeoBounds.java

@@ -128,7 +128,7 @@ public InternalAggregation doReduce(List<InternalAggregation> aggregations, Redu
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else if (path.size() == 1) {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalGeoCentroid.java

@@ -126,7 +126,7 @@ public InternalGeoCentroid doReduce(List<InternalAggregation> aggregations, Redu
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else if (path.size() == 1) {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalNumericMetricsAggregation.java

@@ -20,6 +20,7 @@
 
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationExecutionException;
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 
@@ -52,7 +53,7 @@ public String getValueAsString() {
         }
 
         @Override
-        public Object getProperty(List<String> path) {
+        public Object getProperty(List<String> path, boolean allowMultiBucket) {
             if (path.isEmpty()) {
                 return this;
             } else if (path.size() == 1 && "value".equals(path.get(0))) {
@@ -83,8 +84,13 @@ public String valueAsString(String name) {
         }
 
         @Override
-        public Object getProperty(List<String> path) {
+        public Object getProperty(List<String> path, boolean allowMultiBucket) {
             if (path.isEmpty()) {
+                if (allowMultiBucket == false) {
+                    throw new AggregationExecutionException("[" + getName() + "] is a [" + getType()
+                        + "] which contains multiple values, but only number value or a single value numeric metric aggregation.  Please " +
+                        "specify which value to return.");
+                }
                 return this;
             } else if (path.size() == 1) {
                 return value(path.get(0));

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalScriptedMetric.java

@@ -115,7 +115,7 @@ public InternalAggregation doReduce(List<InternalAggregation> aggregations, Redu
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else if (path.size() == 1 && "value".equals(path.get(0))) {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/InternalTopHits.java

@@ -165,7 +165,7 @@ public InternalAggregation doReduce(List<InternalAggregation> aggregations, Redu
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else {

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketHelpers.java

@@ -155,7 +155,7 @@ public static Double resolveBucketValue(MultiBucketsAggregation agg,
     public static Double resolveBucketValue(MultiBucketsAggregation agg,
             InternalMultiBucketAggregation.InternalBucket bucket, List<String> aggPathAsList, GapPolicy gapPolicy) {
         try {
-            Object propertyValue = bucket.getProperty(agg.getName(), aggPathAsList);
+            Object propertyValue = bucket.getProperty(agg.getName(), aggPathAsList, false);
             if (propertyValue == null) {
                 throw new AggregationExecutionException(AbstractPipelineAggregationBuilder.BUCKETS_PATH_FIELD.getPreferredName()
                         + " must reference either a number value or a single value numeric metric aggregation");

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalBucketMetricValue.java

@@ -90,7 +90,7 @@ public InternalAggregation doReduce(List<InternalAggregation> aggregations, Redu
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else if (path.size() == 1 && "value".equals(path.get(0))) {

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/InternalDerivative.java

@@ -71,7 +71,7 @@ DocValueFormat formatter() {
     }
 
     @Override
-    public Object getProperty(List<String> path) {
+    public Object getProperty(List<String> path, boolean allowMultiBucket) {
         if (path.isEmpty()) {
             return this;
         } else if (path.size() == 1 && "value".equals(path.get(0))) {