Merge pull request #126 from einorler/pipeline_avg_bucket

Added avg_bucket pipeline aggregation

docs/Aggregation/Pipeline/AvgBucket.md

+# Avg Bucket Aggregation
+
+> More info about avg bucket aggregation is in the [official elasticsearch docs][1]
+
+A sibling pipeline aggregation which calculates the (mean) average value of a specified metric in a 
+sibling aggregation. The specified metric must be numeric and the sibling aggregation must be a multi-bucket 
+aggregation.
+
+## Simple example
+
+```JSON
+{
+    "aggs" : {
+        "sales_per_month" : {
+            "date_histogram" : {
+                "field" : "date",
+                "interval" : "month"
+            },
+            "aggs": {
+                "sales": {
+                    "sum": {
+                        "field": "price"
+                    }
+                }
+            }
+        },
+        "avg_monthly_sales": {
+            "avg_bucket": {
+                "buckets_path": "sales_per_month>sales" 
+            }
+        }
+    }
+}
+```
+
+And now the query via DSL:
+
+```php
+$search = new Search();
+
+$dateAggregation = new DateHistogramAggregation('sales_per_month', 'date', 'month');
+$dateAggregation->addAggregation(
+    new SumAggregation('sales', 'price')
+);
+
+$search->addAggregation($dateAggregation);
+$search->addAggregation(
+    new AvgBucketAggregation('avg_monthly_sales', 'sales_per_month>sales')
+);
+
+$aggArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-avg-bucket-aggregation.html

src/Aggregation/Pipeline/AvgBucketAggregation.php

+<?php
+
+/*
+ * This file is part of the ONGR package.
+ *
+ * (c) NFQ Technologies UAB <info@nfq.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace ONGR\ElasticsearchDSL\Aggregation\Pipeline;
+
+/**
+ * Class representing Avg Bucket Pipeline Aggregation.
+ *
+ * @link https://goo.gl/SWK2nP
+ */
+class AvgBucketAggregation extends AbstractPipelineAggregation
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getType()
+    {
+        return 'avg_bucket';
+    }
+}

tests/Aggregation/Pipeline/AvgBucketAggregationTest.php

+<?php
+
+/*
+ * This file is part of the ONGR package.
+ *
+ * (c) NFQ Technologies UAB <info@nfq.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace ONGR\ElasticsearchDSL\Tests\Aggregation\Pipeline;
+
+use ONGR\ElasticsearchDSL\Aggregation\Pipeline\AvgBucketAggregation;
+
+/**
+ * Unit test for avg_bucket aggregation.
+ */
+class AvgBucketAggregationTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * Tests getArray method.
+     */
+    public function testGetArray()
+    {
+        $aggregation = new AvgBucketAggregation('foo', 'foo>bar');
+
+        $this->assertEquals(['buckets_path' => 'foo>bar'], $aggregation->getArray());
+    }
+
+    /**
+     * Tests getType method.
+     */
+    public function testAvgBucketAggregationGetType()
+    {
+        $aggregation = new AvgBucketAggregation('foo', 'foo>bar');
+        $this->assertEquals('avg_bucket', $aggregation->getType());
+    }
+}