SERVER-5710 Changed KeyPattern.hasField() sematics to consider dotted field prefixes.

1 files changed, 117 insertions, 0 deletions

diff --git a/src/mongo/db/field_ref.h b/src/mongo/db/field_ref.h
new file mode 100644
index 00000000000..ea7b7dab34d
--- /dev/null
+++ b/src/mongo/db/field_ref.h
@@ -0,0 +1,117 @@
+/**
+ *    Copyright (C) 2012 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/>.
+ */
+
+#pragma once
+
+#include <boost/scoped_array.hpp>
+#include <string>
+#include <vector>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/string_data.h"
+
+namespace mongo {
+
+    /**
+     * A FieldPath represents a path in a document, starting from the root. The path
+     * is made of "field parts" separated by dots. The class provides an efficient means to
+     * "split" the dotted fields in its parts, but no validation is done.
+     *
+     * Any field part may be replaced, after the "original" field reference was parsed. Any
+     * part can be accessed through a StringData object.
+     *
+     * The class is not thread safe.
+     */
+    class FieldRef {
+        MONGO_DISALLOW_COPYING(FieldRef);
+    public:
+        FieldRef() : _size(0) {}
+
+        /**
+         * Field parts accessed through getPart() calls no longer would be valid, after the
+         * destructor ran.
+         */
+        ~FieldRef() {}
+
+        /**
+         * Builds a field path out of each field part in 'dottedField'.
+         */
+        void parse(const StringData& dottedField);
+
+        /**
+         * Sets the 'i-th' field part to point to 'part'. Assumes i < size(). Behavior is
+         * undefined otherwise.
+         */
+        void setPart(size_t i, const StringData& part);
+
+        /**
+         * Returns the 'i-th' field part. Assumes i < size(). Behavior is undefined otherwise.
+         */
+        StringData getPart(size_t i) const;
+
+        /**
+         * Returns a copy of the full dotted field in its current state (i.e., some parts may
+         * have been replaced since the parse() call).
+         */
+        std::string dottedField() const;
+
+        /**
+         * Resets the internal state. See note in parse() call.
+         */
+        void clear();
+
+        //
+        // accessors
+        //
+
+        /**
+         * Returns the number of parts in this FieldRef.
+         */
+        size_t numParts() const { return _size; }
+
+        /**
+         * Returns the number of fields parts that were replaced so far. Replacing the same
+         * fields several times only counts for 1.
+         */
+        size_t numReplaced() const;
+
+    private:
+        // Dotted fields are most often not longer than three parts. We use a mixed structure
+        // here that will not require any extra memory allocation when that is the case. And
+        // handle larger dotted fields if it is. The idea is not to penalize the common case
+        // with allocations.
+        static const size_t kReserveAhead = 4;
+
+        size_t _size;                                // # of field parts stored
+        StringData _fixed[kReserveAhead];            // first kResevedAhead field components
+        std::vector<StringData> _variable;           // remaining field components
+
+        // Areas that _fixed and _variable point to.
+        boost::scoped_array<char> _fieldBase;        // concatenation of null-terminated parts
+        std::vector<std::string> _replacements;      // added with the setPart call
+
+        /** Converts the field part index to the variable part equivalent */
+        size_t getIndex(size_t i) const { return i-kReserveAhead; }
+
+        /**
+         * Returns the new number of parts after appending 'part' to this field path. It
+         * assumes that 'part' is pointing to an internally allocated area.
+         */
+        size_t appendPart(const StringData& part);
+
+    };
+
+} // namespace mongo