Consider Neo4J. The fail mode here for MongoDB (complex non-hierarchical relationships) is a win mode for Neo4J. Hierarchies are just a special case of graphs.

Consider Neo4J. The fail mode here for MongoDB (complex non-hierarchical relationships) is a win mode for Neo4J. Hierarchies are just a special case of graphs. Use a proper graph database, and you can actually represent the relationships based the domain model, without the clumsiness of hierarchical NoSQL or even worse clumsiness of RDBMS.