Mongo can index on any field, so it shouldn't be slow to ignore _id. It is akin to a rowid/oid. Although, people seem to have started to use SOLR to index MongoDB (still wrapping my head around this), so maybe your concern is valid.
William P. Riley-Land Sole Proprietor Software Engineer Riley-Land Software http://william.nodejitsu.com/ 573.268.4900 On Apr 7, 2012, at 11:00 AM, hibernate-dev-requ...@lists.jboss.org wrote: > Send hibernate-dev mailing list submissions to > hibernate-dev@lists.jboss.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.jboss.org/mailman/listinfo/hibernate-dev > or, via email, send a message with subject or body 'help' to > hibernate-dev-requ...@lists.jboss.org > > You can reach the person managing the list at > hibernate-dev-ow...@lists.jboss.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of hibernate-dev digest..." > > > Today's Topics: > > 1. [OGM] MongoDB dialect and treatment of _id (Emmanuel Bernard) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 6 Apr 2012 18:41:42 +0200 > From: Emmanuel Bernard <emman...@hibernate.org> > Subject: [hibernate-dev] [OGM] MongoDB dialect and treatment of _id > To: hibernate-dev@lists.jboss.org > Message-ID: <5ad5a697-8c7c-42b7-8df7-b5adddd54...@hibernate.org> > Content-Type: text/plain; charset=us-ascii > > I would like to discuss the problem of _id in MongoDB and how to map that in > Hibernate OGM. > > MongoDB is a bit psycho-rigid in how it uniquely identifies a document. A > special property named _id is used for that and must be unique across a > collection. It is also strongly recommended to let MongoDB generate this id > (a UUID essentially). > > In the MongoDb dialect we have not settled on how to use _id. and I would > like to clarify that. Today we use `dbObject.put(ID_FIELDNAME, > key.getColumnValues()[0])` but that is only correct if the id property is > mapped to a single column. (ie `key.getColumnNames().length == 1`) > > ## Use _id as a OracleDB rowid > > We could decide to use _id as a purely internal identifier for a document and > basically never ever rely on it. All queries and lookup with use the > identifier columns and their value to find a document. > That has the benefit of not having to deal with _id but I don't know if > that's an OK practice in MongoDB or if it's not recommended at all as it > would lead to costly lookups. Anybody familiar with MongoDB can shime in? > > ## Map _id when we have a identifier mapped on one column > > In this case, I will only discuss the case where an id is mapped to a single > column. > We could decide to map the id column value to both the id column and to _id. > That creates some duplication but OGM would be happy and MongoDB's queries > could be efficient. > Alternatively, we could decide to completely ignore the id column name and > use _id for this. The TupleShapshot would then be responsible for binding the > id column name to the value stored in _id. My concern with the alternative is > that someone reading the data from the mongodb store will not find the JPA id > column but rather see _id. On the other hand it seems to be the norm in the > MongoDB land. > > ### Identifiers mapped on several columns > > In this case, we have three approaches that can be combined: > > 1. treat _id as rowid (see avove) > 2. map id values as a complex object and put that in _id eg { "_id": { > "firstname": "Emmanuel", "lastname": "Bernard"} } > > Note that we can then decide to bind the id columns as top level attributes > of the document as well. > > Do you guys have any thoughts on the best approach? > > > ------------------------------ > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev@lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev > > End of hibernate-dev Digest, Vol 70, Issue 9 > ******************************************** _______________________________________________ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
