Utility methods for extracting elements from BSON objects, that return Status.

Code that works with BSON that return Status objects intead of throwing exceptions generate
a lot of boilerplate when using the regular BSON accessor operations.  These functions
consolidate that boilerplate in one place, bson_extract.h/cpp.  It also provides a convenient
location for dropping other generic field extraction methods that return Statuses.

1 files changed, 87 insertions, 0 deletions

diff --git a/src/mongo/bson/util/bson_extract.cpp b/src/mongo/bson/util/bson_extract.cpp
new file mode 100644
index 00000000000..68843fd445e
--- /dev/null
+++ b/src/mongo/bson/util/bson_extract.cpp
@@ -0,0 +1,87 @@
+/*    Copyright 2012 10gen Inc.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+#include "mongo/bson/util/bson_extract.h"
+
+#include "mongo/db/jsobj.h"
+
+namespace mongo {
+
+    Status bsonExtractField(const BSONObj& object,
+                            const StringData& fieldName,
+                            BSONElement* outElement) {
+        BSONElement element = object[fieldName.data()];
+        if (element.eoo())
+            return Status(ErrorCodes::NoSuchKey, std::string(fieldName.data(), fieldName.size()));
+        *outElement = element;
+        return Status::OK();
+    }
+
+    Status bsonExtractTypedField(const BSONObj& object,
+                                 const StringData& fieldName,
+                                 BSONType type,
+                                 BSONElement* outElement) {
+        Status status = bsonExtractField(object, fieldName, outElement);
+        if (!status.isOK())
+            return status;
+        if (type != outElement->type()) {
+            return Status(ErrorCodes::TypeMismatch,
+                          std::string("Expected ") + typeName(type) +
+                          " found " + typeName(outElement->type()));
+        }
+        return Status::OK();
+    }
+
+    Status bsonExtractBooleanFieldWithDefault(const BSONObj& object,
+                                              const StringData& fieldName,
+                                              bool defaultValue,
+                                              bool* out) {
+        BSONElement value;
+        Status status = bsonExtractField(object, fieldName, &value);
+        if (!status.isOK())
+            return status;
+        if (!value.isNumber() && !value.isBoolean())
+            return Status(ErrorCodes::TypeMismatch, "Expected boolean or number type");
+
+        *out = value.trueValue();
+        return Status::OK();
+    }
+
+    Status bsonExtractStringField(const BSONObj& object,
+                                  const StringData& fieldName,
+                                  std::string* out) {
+        BSONElement element;
+        Status status = bsonExtractTypedField(object, fieldName, String, &element);
+        if (!status.isOK())
+            return status;
+        *out = element.str();
+        return Status::OK();
+    }
+
+    Status bsonExtractStringFieldWithDefault(const BSONObj& object,
+                                             const StringData& fieldName,
+                                             const StringData& defaultValue,
+                                             std::string* out) {
+        Status status = bsonExtractStringField(object, fieldName, out);
+        if (status == ErrorCodes::NoSuchKey) {
+            *out = std::string(defaultValue.data(), defaultValue.size());
+        }
+        else if (!status.isOK()) {
+            return status;
+        }
+        return Status::OK();
+    }
+
+}  // namespace mongo