Is modeling relationships in MongoDB using an ODM (Ming) an Anti-Pattern?

Question

I'm interested in using Ming to model my 100+ GB data set which is largely non-relational data (signals measured in a lab) with some "relational" meta-data (e.g. experiment name) in MongoDB. This is not a question about whether or not I should be using a NoSql database.

If modeling relationships using an ODM (e.g. Ming's version here) is a valid design pattern than why aren't any of the other popular ODMs providing that functionality? I didn't see it in any of the following:

-Mongoose (MongoDB)

-cqlengine (Cassandra)

-Hector (Cassandra)

-doctrine (CouchDB)

Answer 1

It's definitely valid to model relationships in a NoSQL data store, although if you have highly relational data you might want to reconsider whether the data store and schema design you have chosen is working with or against your use case goals.

In MongoDB a common decision (based on your use case) is whether it might be more appropriate to model relationships by embedding related data in the same collection or using a reference linking to document(s) in another collection (see: Data Model Design in the MongoDB manual).

Foreign key relationships are typically not populated or enforced with server-side support from distributed NoSQL databases, so declarative references in an ODM often translate into multiple queries on the server. Multiple queries aren't necessarily bad (although there can be poorly written extremes) and an application-level data join using references can be very convenient.

For MongoDB in particular, there is a BSON field type for Database References (DBRefs). There is currently (as at MongoDB 2.6) no support for server-side expansion of DBRefs, however many of the drivers and ODMs provide convenience methods for following and populating references in this standard notation.

You can see this used in a few of the ODMs you've mentioned:

• Mongoose supports population of documents from other collections
• Doctrine ODM supports references mapping relationships to other classes/collections

Typically ODMs offer a choice of either automatic population of references or lazy population (i.e. as needed or accessed in code).

I'm not familiar with the Cassandra libraries, but didn't see any obvious mention of references or relationships in the documentation. I would assume that presence (or absence) of a relationship feature is more a choice of the author(s) of the ODM rather than a specific pattern/antipattern.