SERVER-24766 implement basic views library

Adds the basic infrastructure for read-only non-materialized views, as well as
the ability to create them (but not use them).

Views are disabled by default unless mongod is given the setParameter
enableViews=1.

5 files changed, 308 insertions, 0 deletions

diff --git a/src/mongo/db/views/SConscript b/src/mongo/db/views/SConscript
new file mode 100644
index 00000000000..33e44ae68d8
--- /dev/null
+++ b/src/mongo/db/views/SConscript
@@ -0,0 +1,15 @@
+# -*- mode: python -*-
+
+Import("env")
+
+env.Library(
+    target='views',
+    source=[
+        'view.cpp',
+        'view_catalog.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+        '$BUILD_DIR/mongo/db/server_parameters',
+    ]
+)
diff --git a/src/mongo/db/views/view.cpp b/src/mongo/db/views/view.cpp
new file mode 100644
index 00000000000..380f5eeaed5
--- /dev/null
+++ b/src/mongo/db/views/view.cpp
@@ -0,0 +1,46 @@
+/**
+*    Copyright (C) 2016 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.
+*/
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/views/view.h"
+
+#include "mongo/base/string_data.h"
+
+namespace mongo {
+
+ViewDefinition::ViewDefinition(StringData dbName,
+                               StringData viewName,
+                               StringData viewOnName,
+                               const BSONObj& pipeline)
+    : _viewNss(dbName, viewName), _viewOnNss(dbName, viewOnName) {
+    for (BSONElement e : pipeline) {
+        _pipeline.push_back(e.Obj().getOwned());
+    }
+}
+}  // namespace mongo
diff --git a/src/mongo/db/views/view.h b/src/mongo/db/views/view.h
new file mode 100644
index 00000000000..446d74dffe1
--- /dev/null
+++ b/src/mongo/db/views/view.h
@@ -0,0 +1,79 @@
+/**
+*    Copyright (C) 2016 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 <vector>
+
+#include "mongo/base/string_data.h"
+#include "mongo/bson/bsonobj.h"
+#include "mongo/db/namespace_string.h"
+
+namespace mongo {
+
+/**
+ * Represents a "view": a virtual collection defined by a query on a collection or another view.
+ */
+class ViewDefinition {
+public:
+    /**
+     * Create a new view.
+     *
+     * @param dbName The name of the database owning the view.
+     * @param viewName The name of the view. Does not include the database name.
+     * @param viewOnName The name of the view or collection upon which this view is defined. Does
+     * not include the database name.
+     * @param pipeline A series of pipeline stages representing an aggregation on the `viewOn`
+     * namespace.
+     */
+    ViewDefinition(StringData dbName,
+                   StringData viewName,
+                   StringData viewOnName,
+                   const BSONObj& pipeline);
+
+    /**
+     * @return The fully-qualified namespace of this view.
+     */
+    const NamespaceString& name() const {
+        return _viewNss;
+    }
+
+    /**
+     * @return The fully-qualified namespace of the view or collection upon which this view is
+     * based.
+     */
+    const NamespaceString& viewOn() const {
+        return _viewOnNss;
+    }
+
+private:
+    NamespaceString _viewNss;
+    NamespaceString _viewOnNss;
+    std::vector<BSONObj> _pipeline;
+};
+}  // namespace mongo
diff --git a/src/mongo/db/views/view_catalog.cpp b/src/mongo/db/views/view_catalog.cpp
new file mode 100644
index 00000000000..65197745dd3
--- /dev/null
+++ b/src/mongo/db/views/view_catalog.cpp
@@ -0,0 +1,80 @@
+/**
+*    Copyright (C) 2016 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.
+*/
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/views/view_catalog.h"
+
+#include "mongo/base/string_data.h"
+#include "mongo/db/namespace_string.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/db/server_parameters.h"
+#include "mongo/db/views/view.h"
+
+namespace {
+bool enableViews = false;
+}  // namespace
+
+namespace mongo {
+ExportedServerParameter<bool, ServerParameterType::kStartupOnly> enableViewsParameter(
+    ServerParameterSet::getGlobal(), "enableViews", &enableViews);
+
+const std::uint32_t ViewCatalog::kMaxViewDepth = 20;
+
+ViewCatalog::ViewCatalog(OperationContext* txn, Database* database) {}
+
+Status ViewCatalog::createView(OperationContext* txn,
+                               const NamespaceString& viewName,
+                               const NamespaceString& viewOn,
+                               const BSONObj& pipeline) {
+    if (!enableViews)
+        return Status(ErrorCodes::CommandNotSupported, "View support not enabled");
+
+    if (lookup(StringData(viewName.ns())))
+        return Status(ErrorCodes::NamespaceExists, "Namespace already exists");
+
+    if (viewName.db() != viewOn.db())
+        return Status(ErrorCodes::BadValue,
+                      "View must be created on a view or collection in the same database");
+
+    BSONObj ownedPipeline = pipeline.getOwned();
+    txn->recoveryUnit()->onCommit([this, viewName, viewOn, ownedPipeline]() {
+        _viewMap[viewName.ns()] = std::make_shared<ViewDefinition>(
+            viewName.db(), viewName.coll(), viewOn.coll(), ownedPipeline);
+    });
+    return Status::OK();
+}
+
+ViewDefinition* ViewCatalog::lookup(StringData ns) {
+    ViewMap::const_iterator it = _viewMap.find(ns);
+    if (it != _viewMap.end()) {
+        return it->second.get();
+    }
+    return nullptr;
+}
+}  // namespace mongo
diff --git a/src/mongo/db/views/view_catalog.h b/src/mongo/db/views/view_catalog.h
new file mode 100644
index 00000000000..0dd3f34a80e
--- /dev/null
+++ b/src/mongo/db/views/view_catalog.h
@@ -0,0 +1,88 @@
+/**
+*    Copyright (C) 2016 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/views/view.h"
+#include "mongo/util/string_map.h"
+
+namespace mongo {
+class Database;
+class NamespaceString;
+class OperationContext;
+class Status;
+class StringData;
+
+/**
+ * In-memory data structure for view definitions. Note that this structure is not thread-safe; you
+ * must be holding a database lock to access a database's view catalog.
+ */
+class ViewCatalog {
+    MONGO_DISALLOW_COPYING(ViewCatalog);
+
+public:
+    // TODO(SERVER-23700): Make this a unique_ptr once StringMap supports move-only types.
+    using ViewMap = StringMap<std::shared_ptr<ViewDefinition>>;
+    static const std::uint32_t kMaxViewDepth;
+
+    ViewCatalog(OperationContext* txn, Database* database);
+
+    ViewMap::const_iterator begin() const {
+        return _viewMap.begin();
+    }
+
+    ViewMap::const_iterator end() const {
+        return _viewMap.end();
+    }
+
+    /**
+     * Create a new view.
+     *
+     * @param viewName The name of the view being created.
+     * @param viewOn The name of the view or collection upon which this view is defined.
+     * @param pipeline The aggregation pipeline that defines the aggregation on the backing
+     * namespace.
+     */
+    Status createView(OperationContext* txn,
+                      const NamespaceString& viewName,
+                      const NamespaceString& viewOn,
+                      const BSONObj& pipeline);
+
+    /**
+     * Look up the namespace in the view catalog, returning a pointer to a View definition, or
+     * nullptr if it doesn't exist. Note that the caller does not own the pointer.
+     *
+     * @param ns The full namespace string of the view.
+     * @return A bare pointer to a view definition if ns is a valid view with a backing namespace.
+     */
+    ViewDefinition* lookup(StringData ns);
+
+private:
+    ViewMap _viewMap;
+};
+}  // namespace mongo