MongoDB: Introduction 2

How the drivers work

All MongoDB drivers perform three major functions.

First, they generateMongoDB object IDs. These are the default values stored in the _id field of all docu-
ments.

Next, the drivers convert any language-specific representation of documents to and from BSON, the binary data format used by MongoDB. In the foregoing examples, the driver serializes all the Ruby hashes into BSON and then deserializes the BSON that’s returned from the database back to Ruby hashes.
Final,the drivers is to communicate with the database over a TCP socket using the MongoDB wire protocol.

 

Object ID generation

Every MongoDB document requires a primary key. That key, which must be unique for all documents in each collection, is referenced by a document’s _id field. Developers are free to use their own custom values as the _id, but when not provided, a MongoDB object ID will be used. Before sending a document to the server, the driver checks whether the _id field is present. If the field is missing, an object ID proper will be generated and stored as _id.

BSON

BSON is the binary format used to represent documents in MongoDB. BSON acts as both a storage and command format: all documents are stored on disk as BSON, and all queries and commands are specified using BSON documents. Consequently, all MongoDB drivers must be able to translate between some language-specific document representation and BSON.