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/**
* Copyright (C) 2013 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.
*/
#pragma once
#include "mongo/base/status.h"
#include "mongo/base/string_data.h"
#include "mongo/bson/mutable/element.h"
#include "mongo/db/field_ref.h"
#include "mongo/db/jsobj.h"
namespace mongo {
class LogBuilder;
/**
* Abstract base class for update "modifiers" (a.k.a "$ operators"). To create a new
* operator, implement a new derived class.
*
* A typical call sequence for the class is:
*
* + init() with the mod arguments
*
* + For each document that is being touched on that update, the following methods are
* going to be called once for that document and in the order the calls appear here.
*
* + prepare() to check if mod is viable over the document
*
* + apply(), effectively computing the update
*
* + log() registering the change in the log for replication purposes
*
* Again, a modifier implementation may rely on these last three calls being made and in
* that particular order and therefore can keep and reuse state between these calls, when
* appropriate.
*
* TODO:
* For a reference implementation, see modifier_identity.{h,cpp} used in tests.
*/
class ModifierInterface {
public:
virtual ~ModifierInterface() { }
struct Options;
/**
* Returns OK and extracts the parameters for this given mod from 'modExpr'. For
* instance, for a $inc, extracts the increment value. The init() method would be
* called only once per operand, that is, if a { $inc: { a: 1, b: 1 } } is issued,
* there would be one instance of the operator working on 'a' and one on 'b'. In each
* case, init() would be called once with the respective bson element.
*
* If 'modExpr' is invalid, returns an error status with a reason description.
*
* The optional bool out parameter 'positional', if provided, will be set to 'true' if
* the mod requires matched field details to be provided when calling 'prepare'. The
* field is optional since this is a hint to the caller about what work is needed to
* correctly invoke 'prepare'. It is always legal to provide any match details
* unconditionally. The value set in 'positional' if any, is only meaningful if 'init'
* returns an OK status.
*
* Note:
*
* + An operator may assume the modExpr passed here will be unchanged throughout all
* the mod object lifetime and also that the modExrp's lifetime exceeds the life
* time of this mod. Therefore, taking references to elements inside modExpr is
* valid.
*/
virtual Status init(const BSONElement& modExpr, const Options& opts,
bool* positional = NULL) = 0;
/**
* Returns OK if it would be correct to apply this mod over the document 'root' (e.g, if
* we're $inc-ing a field, is that field numeric in the current doc?).
*
* If the field this mod is targeted to contains a $-positional parameter, that value
* can be bound with 'matchedField', passed by the caller.
*
* In addition, the call also identifies which fields(s) of 'root' the mod is interested
* in changing (note that the modifier may want to add a field that's not present in
* the document). The call also determines whether it could modify the document in
* place and whether it is a no-op for the given document. All this information is in
* the passed 'execInfo', which is filled inside the call.
*
* If the mod cannot be applied over 'root', returns an error status with a reason
* description.
*
* Note that you must provide a meaningful 'matchedField' here, unless 'init' set
* 'positional' to 'false', in which case you may pass an empty StringData object.
*/
struct ExecInfo;
virtual Status prepare(mutablebson::Element root,
const StringData& matchedField,
/* IN-OUT */ ExecInfo* execInfo) = 0;
/**
* Returns OK and modifies (or adds) an element (or elements) from the 'root' passed on
* the prepareMod call. This may act on multiple fields but should only be called once
* per operator.
*
* For this call to be issued, the call to 'prepareElem' must have necessarily turned
* off 'ExecInfo.noOp', ie this mod over this document is not a no-op.
*
* If the mod could not be applied, returns an error status with a reason description.
*/
virtual Status apply() const = 0 ;
/**
* Returns OK and records the result of this mod in the provided LogBuilder. The mod
* must have kept enough state to be able to produce the log record (see idempotency
* note below). This call may be issued even if apply() was not.
*
* If the mod could not be logged, returns an error status with a reason description.
*
* Idempotency Note:
*
* + The modifier must log a mod that is idempotent, ie, applying it more than once
* to a base collection would produce the same result as applying it only once. For
* example, a $inc can be switched to a $set for the resulting incremented value,
* for logging purposes. An array based operator may check the contents of the
* array before operating on it.
*/
virtual Status log(LogBuilder* logBuilder) const = 0;
};
/**
* Options used to control Modifier behavior
*/
struct ModifierInterface::Options {
Options() : fromReplication(false), enforceOkForStorage(true) {}
Options(bool repl, bool ofs) : fromReplication(repl), enforceOkForStorage(ofs) {}
static Options normal() { return Options(false, true); }
static Options fromRepl() { return Options(true, false); }
static Options unchecked() { return Options(false, false); }
bool fromReplication;
bool enforceOkForStorage;
};
struct ModifierInterface::ExecInfo {
static const int MAX_NUM_FIELDS = 2;
/**
* An update mod may specify that it wishes to the applied only if the context
* of the update turns out a certain way.
*/
enum UpdateContext {
// This mod wants to be applied only if the update turns out to be an insert.
INSERT_CONTEXT,
// This mod wants to be applied only if the update is not an insert.
UPDATE_CONTEXT,
// This mod doesn't care if the update will be an update or an upsert.
ANY_CONTEXT
};
ExecInfo() : noOp(false), context(ANY_CONTEXT) {
for (int i = 0; i < MAX_NUM_FIELDS; i++) {
fieldRef[i] = NULL;
}
}
// The fields of concern to the driver: no other op may modify the fields listed here.
FieldRef* fieldRef[MAX_NUM_FIELDS]; // not owned here
bool noOp;
UpdateContext context;
};
} // namespace mongo
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