Ommi v0.1.8 adds support for composite keys and complex queries involving an arbitrary number of models.
Complex queries work automagically so long as models define ReferenceTo annotations. Ommi handles generating the necessary sub-queries/joins for SQLite/PostgreSQL and aggregations for MongoDB. The following find sub-methods support complex queries:
countdeletefetchset
Composite keys are similarly handled automagically, so long as models define Key annotations. Ommi generates the appropriate queries to perform joins and aggregations using the declared composite keys.