SERVER-24879 Add $mergeObjects aggregation expression

1 files changed, 93 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/accumulator_merge_objects.cpp b/src/mongo/db/pipeline/accumulator_merge_objects.cpp
new file mode 100644
index 00000000000..1584d8ba2c4
--- /dev/null
+++ b/src/mongo/db/pipeline/accumulator_merge_objects.cpp
@@ -0,0 +1,93 @@
+/**
+ * Copyright (c) 2017 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/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects for
+ * all of the code used other than as permitted herein. If you modify file(s)
+ * with this exception, you may extend this exception to your version of the
+ * file(s), but you are not obligated to do so. If you do not wish to do so,
+ * delete this exception statement from your version. If you delete this
+ * exception statement from all source files in the program, then also delete
+ * it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/pipeline/accumulator.h"
+
+#include "mongo/db/pipeline/accumulation_statement.h"
+#include "mongo/db/pipeline/expression.h"
+#include "mongo/db/pipeline/value.h"
+
+namespace mongo {
+
+using boost::intrusive_ptr;
+
+/* ------------------------- AccumulatorMergeObjects ----------------------------- */
+
+REGISTER_ACCUMULATOR(mergeObjects, AccumulatorMergeObjects::create);
+REGISTER_EXPRESSION(mergeObjects, ExpressionFromAccumulator<AccumulatorMergeObjects>::parse);
+
+const char* AccumulatorMergeObjects::getOpName() const {
+    return "$mergeObjects";
+}
+
+intrusive_ptr<Accumulator> AccumulatorMergeObjects::create(
+    const boost::intrusive_ptr<ExpressionContext>& expCtx) {
+    return new AccumulatorMergeObjects(expCtx);
+}
+
+AccumulatorMergeObjects::AccumulatorMergeObjects(
+    const boost::intrusive_ptr<ExpressionContext>& expCtx)
+    : Accumulator(expCtx) {
+    _memUsageBytes = sizeof(*this);
+}
+
+void AccumulatorMergeObjects::reset() {
+    _memUsageBytes = sizeof(*this);
+    _output.reset();
+}
+
+void AccumulatorMergeObjects::processInternal(const Value& input, bool merging) {
+    if (input.nullish()) {
+        return;
+    }
+
+    uassert(40400,
+            str::stream() << "$mergeObjects requires object inputs, but input " << input.toString()
+                          << " is of type "
+                          << typeName(input.getType()),
+            (input.getType() == BSONType::Object));
+
+    FieldIterator iter = input.getDocument().fieldIterator();
+    while (iter.more()) {
+        Document::FieldPair pair = iter.next();
+        // Ignore missing values only, null and undefined are still considered.
+        if (pair.second.missing())
+            continue;
+
+        _output.setField(pair.first, pair.second);
+    }
+    _memUsageBytes = sizeof(*this) + _output.getApproximateSize();
+}
+
+Value AccumulatorMergeObjects::getValue(bool toBeMerged) {
+    return _output.freezeToValue();
+}
+
+}  // namespace mongo