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/**
* Copyright (C) 2017 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/update/update_leaf_node.h"
#include "mongo/stdx/memory.h"
namespace mongo {
/**
* The apply() function for an update modifier must
* 1) update the element at the update path if it exists;
* 2) raise a user error, indicate a no-op, or create and initialize a new element if the update
* path does not exist, depending on the specific modifier semantics;
* 3) check for any changes that modify an immutable path;
* 4) determine whether indexes may be affected;
* 5) validate that the updated document is valid for storage; and
* 6) create an oplog entry for the update.
* ModifierNode provides a generic implementation of the apply() function that does all this heavy
* lifting and calls out to modifier-specific overrides that customize apply() behavior where
* necessary.
*/
class ModifierNode : public UpdateLeafNode {
public:
explicit ModifierNode(Context context = Context::kAll) : UpdateLeafNode(context) {}
ApplyResult apply(ApplyParams applyParams) const final;
protected:
enum class ModifyResult {
// No log entry is necessary for no-op updates.
kNoOp,
// The update can be logged as normal (usually with a $set on the entire element).
kNormalUpdate,
// The element is an array, and the update only appends new array items to the end. The
// update can be logged as a $set on each appended element, rather than including the entire
// array in the log entry.
kArrayAppendUpdate,
// The element did not exist, so it was created then populated with setValueForNewElement().
// The updateExistingElement() method should never return this value.
kCreated
};
/**
* ModifierNode::apply() calls this method when applying an update to an existing path. The
* child's implementation of this method is responsible for updating 'element' and indicating
* what kind of update was performed in its return value.
*/
virtual ModifyResult updateExistingElement(mutablebson::Element* element,
std::shared_ptr<FieldRef> elementPath) const = 0;
/**
* ModifierNode::apply() calls this method when applying an update to a path that does not yet
* exist and should be created. The child's implementation of this method is responsible for
* assigning a value to the new element, which will initially be null.
*
* This method only gets called when the child class implementation of allowCreation() returns
* true. ModiferNode child classes should override setValueForNewElement() iff allowCreation()
* returns true.
*/
virtual void setValueForNewElement(mutablebson::Element* element) const {
// Only implementations that return true for allowCreation() will override this method.
MONGO_UNREACHABLE;
};
/**
* ModifierNode::apply() calls this method after it finishes applying its update to validate
* that no changes resulted in an invalid document. See the implementation of
* storage_validation::storageValid() for more detail about document validation requirements.
* Most ModifierNode child classes can use the default implementation of this method.
*
* - 'updatedElement' is the element that was set by either updateExistingElement() or
* setValueForNewElement().
* - 'leftSibling' and 'rightSibling' are the left and right siblings of 'updatedElement' or
* are invalid if 'updatedElement' is the first or last element in its object, respectively.
* If a ModifierNode deletes an element as part of its update (as $unset does),
* 'updatedElement' will be invalid, but validateUpdate() can use the siblings to perform
* validation instead.
* - 'recursionLevel' is the document nesting depth of the 'updatedElement' field.
* - 'modifyResult' is either the value returned by updateExistingElement() or the value
* ModifyResult::kCreated.
*/
virtual void validateUpdate(mutablebson::ConstElement updatedElement,
mutablebson::ConstElement leftSibling,
mutablebson::ConstElement rightSibling,
std::uint32_t recursionLevel,
ModifyResult modifyResult) const;
/**
* ModifierNode::apply() calls this method after validation to create an oplog entry for the
* applied update. Most ModifierNode child classes can use the default implementation of this
* method, which creates a $set entry using 'pathTaken' for the path and 'element' for the
* value.
*
* - 'logBuilder' provides the interface for appending log entries.
* - 'pathTaken' is the path of the applied update.
* - 'element' is the element that was set by either updateExistingElement() or
* setValueForNewElement().
* - 'modifyResult' is either the value returned by updateExistingElement() or the value
* ModifyResult::kCreated.
*/
virtual void logUpdate(LogBuilder* logBuilder,
StringData pathTaken,
mutablebson::Element element,
ModifyResult modifyResult) const;
/**
* ModifierNode::apply() calls this method to determine what to do when applying an update to a
* path that does not exist. If the child class overrides this method to return true,
* ModifierNode::apply() will create a new element at the path and call setValueForNewElement()
* on it. Child classes must implement setValueForNewElement() iff this function returns true.
*/
virtual bool allowCreation() const {
return false;
}
/**
* When allowCreation() returns false, ModiferNode::apply() calls this method when determining
* if an update to a non-existent path is a no-op or an error. When allowNonViablePath() is
* false, an update to a path that could be created (i.e. a "viable" path) is a no-op, and an
* update to a path that could not be created results in a PathNotViable user error. When
* allowNonViablePath() is true, there is no viabilty check, and any update to a nonexistent
* path is a no-op.
*/
virtual bool allowNonViablePath() const {
return false;
}
/**
* When it is possible for updateExistingElement to replace the element's contents with an
* object value (e.g., {$set: {a: {c: 1}}} applied to the document {a: {b:1}}),
* ModifierNode::apply() has to do extra work to determine if any immutable paths have been
* modified. Any ModifierNode child class that can perform such an update should override this
* method to return true, so that ModifierNode::apply() knows to do the extra checks.
*/
virtual bool canSetObjectValue() const {
return false;
}
private:
ApplyResult applyToNonexistentElement(ApplyParams applyParams) const;
ApplyResult applyToExistingElement(ApplyParams applyParams) const;
};
} // namespace mongo
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