1 files changed, 87 insertions, 0 deletions
diff --git a/src/mongo/db/pipeline/accumulator_avg.cpp b/src/mongo/db/pipeline/accumulator_avg.cpp
new file mode 100755
index 00000000000..3e69b204fbb
--- /dev/null
+++ b/src/mongo/db/pipeline/accumulator_avg.cpp
@@ -0,0 +1,87 @@
+/**
+ * Copyright (c) 2011 10gen Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "pch.h"
+#include "accumulator.h"
+
+#include "db/pipeline/document.h"
+#include "db/pipeline/expression_context.h"
+#include "db/pipeline/value.h"
+
+namespace mongo {
+
+    const char AccumulatorAvg::subTotalName[] = "subTotal";
+    const char AccumulatorAvg::countName[] = "count";
+
+    intrusive_ptr<const Value> AccumulatorAvg::evaluate(
+        const intrusive_ptr<Document> &pDocument) const {
+        if (!pCtx->getDoingMerge()) {
+            Super::evaluate(pDocument);
+        }
+        else {
+            /*
+              If we're in the router, we expect an object that contains
+              both a subtotal and a count.  This is what getValue() produced
+              below.
+             */
+            intrusive_ptr<const Value> prhs(vpOperand[0]->evaluate(pDocument));
+            verify(prhs->getType() == Object);
+            intrusive_ptr<Document> pShardDoc(prhs->getDocument());
+
+            intrusive_ptr<const Value> pSubTotal(pShardDoc->getValue(subTotalName));
+            verify(pSubTotal.get());
+            doubleTotal += pSubTotal->getDouble();
+                
+            intrusive_ptr<const Value> pCount(pShardDoc->getValue(countName));
+            verify(pCount.get());
+            count += pCount->getLong();
+        }
+
+        return Value::getZero();
+    }
+
+    intrusive_ptr<Accumulator> AccumulatorAvg::create(
+        const intrusive_ptr<ExpressionContext> &pCtx) {
+        intrusive_ptr<AccumulatorAvg> pA(new AccumulatorAvg(pCtx));
+        return pA;
+    }
+
+    intrusive_ptr<const Value> AccumulatorAvg::getValue() const {
+        if (!pCtx->getInShard()) {
+            double avg = 0;
+            if (count)
+                avg = doubleTotal / static_cast<double>(count);
+
+            return Value::createDouble(avg);
+        }
+
+        intrusive_ptr<Document> pDocument(Document::create());
+        pDocument->addField(subTotalName, Value::createDouble(doubleTotal));
+        pDocument->addField(countName, Value::createLong(count));
+
+        return Value::createDocument(pDocument);
+    }
+
+    AccumulatorAvg::AccumulatorAvg(
+        const intrusive_ptr<ExpressionContext> &pTheCtx):
+        AccumulatorSum(),
+        pCtx(pTheCtx) {
+    }
+
+    const char *AccumulatorAvg::getOpName() const {
+        return "$avg";
+    }
+}