Merge pull request #134 from einorler/pipeline_cumulative_sum

Added cumulative sum pipeline aggregation

docs/Aggregation/Pipeline/CumulativeSum.md

+# Cumulative Sum Aggregation
+
+> More info about cumulative sum aggregation is in the [official elasticsearch docs][1]
+
+A parent pipeline aggregation which calculates the cumulative sum of a specified metric 
+in a parent histogram (or date_histogram) aggregation. The specified metric must be numeric 
+and the enclosing histogram must have min_doc_count set to 0 (default for histogram 
+aggregations).
+
+## Simple example
+
+```JSON
+{
+    "aggs" : {
+        "sales_per_month" : {
+            "date_histogram" : {
+                "field" : "date",
+                "interval" : "month"
+            },
+            "aggs": {
+                "sales": {
+                    "sum": {
+                        "field": "price"
+                    }
+                },
+                "cumulative_sales": {
+                    "cumulative_sum": {
+                        "buckets_path": "sales" 
+                    }
+                }
+            }
+        }
+    }
+}
+```
+
+And now the query via DSL:
+
+```php
+$search = new Search();
+
+$dateAggregation = new DateHistogramAggregation('sales_per_month', 'date', 'month');
+$dateAggregation->addAggregation(
+    new SumAggregation('sales', 'price')
+);
+$dateAggregation->addAggregation(
+    new CumulativeSumAggregation('cumulative_sales', 'sales')
+);
+
+$search->addAggregation($dateAggregation);
+
+$aggArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-pipeline-cumulative-sum-aggregation.html
\ No newline at end of file

src/Aggregation/Pipeline/CumulativeSumAggregation.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 Cumulative Sum Pipeline Aggregation.
+ *
+ * @link https://goo.gl/EUzda6
+ */
+class CumulativeSumAggregation extends AbstractPipelineAggregation
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getType()
+    {
+        return 'cumulative_sum';
+    }
+}

tests/Aggregation/Pipeline/CumulativeSumAggregationTest.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\CumulativeSumAggregation;
+
+/**
+ * Unit test for cumulative sum aggregation.
+ */
+class CumulativeSumAggregationTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * Tests toArray method.
+     */
+    public function testToArray()
+    {
+        $aggregation = new CumulativeSumAggregation('acme', 'test');
+
+        $expected = [
+            'cumulative_sum' => [
+                'buckets_path' => 'test',
+            ],
+        ];
+
+        $this->assertEquals($expected, $aggregation->toArray());
+    }
+}