When the ON clause of a JOIN navigates a @ManyToOne or @OneToMany association (e.g., o.customer.name = 'Alice'), Hibernate creates implicit nested TableGroupJoins on the joined TableGroup. The simple $lookup form cannot express this shape. This ticket tracks adding support for it, likely via the pipeline-form $lookup with $expr.

Addressing the source code notes tagged with TODO-HIBERNATE-168 is in scope of this ticket.