1 files changed, 49 insertions, 0 deletions
diff --git a/src/mongo/db/pipeline/accumulator_first.cpp b/src/mongo/db/pipeline/accumulator_first.cpp
new file mode 100755
index 00000000000..53d8f9595e9
--- /dev/null
+++ b/src/mongo/db/pipeline/accumulator_first.cpp
@@ -0,0 +1,49 @@
+/**
+ * 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/value.h"
+
+namespace mongo {
+
+    intrusive_ptr<const Value> AccumulatorFirst::evaluate(
+        const intrusive_ptr<Document> &pDocument) const {
+        verify(vpOperand.size() == 1);
+
+        /* only remember the first value seen */
+        if (!pValue.get())
+            pValue = vpOperand[0]->evaluate(pDocument);
+
+        return pValue;
+    }
+
+    AccumulatorFirst::AccumulatorFirst():
+        AccumulatorSingleValue() {
+    }
+
+    intrusive_ptr<Accumulator> AccumulatorFirst::create(
+        const intrusive_ptr<ExpressionContext> &pCtx) {
+        intrusive_ptr<AccumulatorFirst> pAccumulator(
+            new AccumulatorFirst());
+        return pAccumulator;
+    }
+
+    const char *AccumulatorFirst::getOpName() const {
+        return "$first";
+    }
+}