SERVER-35329 Package agg projection code for use outside of agg execution

1 files changed, 83 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/transformer_interface.h b/src/mongo/db/pipeline/transformer_interface.h
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+++ b/src/mongo/db/pipeline/transformer_interface.h
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+/**
+ * Copyright (C) 2018 MongoDB 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.
+ */
+
+#pragma once
+
+#include "mongo/db/pipeline/dependencies.h"
+#include "mongo/db/pipeline/document.h"
+#include "mongo/db/pipeline/document_source.h"
+#include "mongo/db/query/explain_options.h"
+
+namespace mongo {
+/**
+ * This class defines the minimal interface that every parser wishing to take advantage of
+ * DocumentSourceSingleDocumentTransformation must implement.
+ *
+ * This interface ensures that DocumentSourceSingleDocumentTransformations are passed parsed
+ * objects that can execute the transformation and provide additional features like
+ * serialization and reporting and returning dependencies. The parser must also provide
+ * implementations for optimizing and adding the expression context, even if those functions do
+ * nothing.
+ */
+class TransformerInterface {
+public:
+    enum class TransformerType {
+        kExclusionProjection,
+        kInclusionProjection,
+        kComputedProjection,
+        kReplaceRoot,
+    };
+    virtual ~TransformerInterface() = default;
+    virtual Document applyTransformation(const Document& input) = 0;
+    virtual TransformerType getType() const = 0;
+    virtual void optimize() = 0;
+    virtual DepsTracker::State addDependencies(DepsTracker* deps) const = 0;
+    virtual DocumentSource::GetModPathsReturn getModifiedPaths() const = 0;
+
+    /**
+     * Returns a document describing this transformation. For example, this function will return
+     * {_id: 0, x: 1} for the stage parsed from {$project: {_id: 0, x: 1}}.
+     */
+    virtual Document serializeTransformation(
+        boost::optional<ExplainOptions::Verbosity> explain) const = 0;
+
+    /**
+     * Returns true if this transformer is an inclusion projection and is a subset of
+     * 'proj', which must be a valid projection specification. For example, if this
+     * TransformerInterface represents the inclusion projection
+     *
+     *      {a: 1, b: 1, c: 1}
+     *
+     * then it is a subset of the projection {a: 1, c: 1}, and this function returns
+     * true.
+     */
+    virtual bool isSubsetOfProjection(const BSONObj& proj) const {
+        return false;
+    }
+};
+}  // namespace mongo